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The ventilatory current and ctenidial function related to oxygen uptake in declining oxygen tension by the mussel Mytilus edulis L.
THE VENTILATORY CURRENT AND CTENIDIAL FUNCTION RELATED TO OXYGEN UPTAKE IN DECLINING OXYGEN TENSION BY THE MUSSEL MYTILUS EDULZS L. P. FAMME and L. H. K~FOED Institute of Biology, Odense University, 5230 Odense M, Denmark (Recrised 17 September 1979) Abstract-l. The oxygen uptake in the mussel Mvtilus edulis is hyperbolic related to declining oxygen tension, indicated by the exhaustion of ali available oxygen and the asymptotic oxygen uptake rate at hyperoxic conditions. 2. Using artificial water irrigation of the mantle cavity, ranging from 2.9 to !6.4Ijhr, the oxygen consumption rate of starved specimens increases by a factor at I .4. 3. The artificial irrigation seems to determine both the level of oxygen cohsumption at high oxygen tensions, and the dependency of oxygen consumption at declining oxygen tension. 4. The oxygen uptake takes place over the entire, undifferentiated body surface, indicating that large amounts of water transported across the ctenidia mainly serve a feeding function. 5. It is therefore postulated that the ctenidia of Mytilus edulis serve mainly a feeding function.
INTRODLICTION The
ctenidia of suspension feeding bivalves serve a dua1 function in bringing about a ciliary induced water movement through the mantle cavity, and in the clearance of particles from this water, as reviewed by Jorgensen (1966). Beyond these functions the ctenidia have been suggested to take an active part in the oxygen uptake and the regulation of oxygen consumption in declining oxygen tension in Mytilws edulis (Bayne, 1971b; Mangum & Burnett, 1975) and Mercenaria mercenaria (Hamwi & Ha&in, 1968), primarily by regulating the ctenidial perfusion relative to the ventilatory current. Several investigators e.g. Krogh (1941), Ghiretti (I966), Owen (1966), and Jorgensen (1966) have stressed that the respiratory function of the ventilatory current is incidental to the feeding function, and Schmidt-Nielsen (1975) proposed the ctenidia to function only in filter-feeding, whereas the gas exchange is primarily cutaneous. DifficuIt~es in measuring directly the various parameters that are known to be important in effecting oxygen uptake through a “gill-type” of gas exchanger (Dejours, 1972), primarily the parameters of perfusion (Bayne, 1971b), has impeded the understanding of the ctenidial participation in the oxygen uptake by .~~f~~~s e&&s. This is partly due to the nonsimultaneous and indirect determination of other respiratory components, the oxygen extraction coefficient and the ventilation rate. Fhigel & Schlieper (1962) and Theede (1963) suggested that the reduced rate of water transport under conditions of starvation implies a cessation in the “preparedness” of the organism to feeding activity, indicating the water transport during starvation to be mainly of respiratory significance. Under conditions of declining oxygen tension, starvation over a period of at least 30 days is known to
induce dependency between oxygen consumption and oxygen tension (Bayne, 1971a), and a reduction in oxygen consumption as found in M~lti~us edu~is (Bayne et al., 1973) and in ~~ti~us cal~r~ja~us (Bayne et al., 1975). Bayne et al. (1976a) suggested the reduction in oxygen consumption following starvation to be primarily due to reduced costs of ventilatory activity, whereas the change in dependency between oxygen consumption and oxygen tension is connected with a metabolic shift from active to standard metabolism. However, Jorgensen (1952; 1960) found in different bivalves, including Mytilus edulis, that the rate of water transport could be kept constant under conditions when the rate of oxygen uptake were reduced. The main purpose of the present study has been to investigate the participation of the ventilatory current and ctenidia in oxygen uptake by Mytilus edulis in declining oxygen tension, by means of simultaneous measurement of the components of the external gas exchange. These components are the oxygen tension, the oxygen extraction coefficient, the oxygen consumption, and the ventilation rate. MATERIALS AND METHODS
The experiments of part I were carried out at the Marine Biological Laboratory of Aarhus University, Ronbjerg, Denmark, in late August, 1978. Specimens of Mytilus edulis, with a mean length of 7 cm, were collected from the upper intertidal zone in the vicinity of the laboratory. The mussels were stored at least 2 days prior to labaratory recordings in an aquarium with running, aerated sea water. The water temperature varied between 16.0 and lS.O”C throughout the experimental period, whereas the salinity was constant at 24”:,,. The mussels were unfed throughout the experimental period, and kept with constant degree of valve opening (with an angle of 3.5”) by means of a glass
161
I62
P. F.AMM~ and L. H. KOFOEI>
tube inserted between the shell valves at the inhafant aperture. The valves were held in position by means of an anteriorly placed rubber band. The experiments of part II were carried oui at the Biological laboratory of Odense University, Denmark, in the late autumn and winter. 197X/79.The mussels (mean length of 7cm) were collected at Kertmge Nor. Denmark, and stored in large containers with aerated sea water at least 14 days before used in experiments. The acciimation and experimental temperature was IWC and the salinity was 17.I’:,<,.The mussels were unfed throughout the storage and experiment& period, and without any determinated degree of valve opening during the storage, whereas during experiments the mussels were kept with constant degre of valve opening as above. Variation in the degree of valve opening during storage was examined at several mussels under laboratory conditions. The musseis were tixed at the one shell valve at the bottom of an aquarium, whereas the other sheil valve was connected to an electrical transducer (linear potentiometer]. and the output monitored on a multicb~rli~ei recorder ~Fhjl~jps PM 98.13). The practlwi work consisted of two parts: 1. To measure the oxygen tension of the exhalant water, an outlet from the mantle cavity was made by drilling a 2.1 mm hole in the one shell valve near the exhalant aperture. taking care not to damage the underlying mantle face. A rubber tube with an approximatei~ equal diameter was pushed into the hole, and through it was inserted a hypodermic needle, with an outer diameter of 1.t mm. making a tight fit. The hypodermic needle was carefully pushed 3 mm into the mantle cavity, making a tiny hole in the mantle tissue. The mounting procedure was partially adapted from Wijsman (1975), and studies on survival with needle Inserted under normal laboratory conditions showed no change in the behaviour or survival time. in relation to undisturbed mussels under the same conditions. Prior to measurements. the mussel was plitced in a respiration chamber, and the outlet rrom the mantle cavity mounted to a “butyl” rubber tube passing air proof out of the respi~tion chamber. This tube was seriatly connected to an oxygen electrode chamber and peristaltic pump, and then passed back into the respiration chamber. The water volume outside the respiration chamber was Sml. giving an entire volume of the measuring system of 100ml. The mussel was left undisturbed for at least I hr in the open, aerated respiration chamber prior to expcrimental start. At the start OF the experiment the respiration chamber was closed, avoiding any air bubbles, and the peristaltic pump started with a constant Row of 275 mtlhr. The small suction of water from the exhalant part of the mantle cavity did not seem to affect the mussel. in that the activity and position of the mantle edges of the inhalant and exhalant apertures showed no response when the peristaltic pump was shut on and off several times with short intervals. The water in the respiration chamber was well stirred by means of an magnetic stirrer in the bottom of the chamber, separated from the musselby a small piece of glass. The temperature of the entire apparatus was controfled by immersion into running sea water. The oxygen tension of the water in the respiration chamber was continuously monitored with a Radiometer (TOX 40) oxygen electrode directly inserted into the respiration chamber, whereas the oxygen tension of the exhalant water was monitored in the etectrode chamber outside the respiration chamber with a similar electrode, using for both electrodes a Radiometer (TOX JO) ox~transmitter system. The electrode signals were cuntinuously recorded on B mu~ticb~l~e~ recorder (Phillips PiLf 9833).
From the oxygen concentration of mspired and expired water, the oxygen extraction coefficient (Dejours, 1977). the oxygen ~onsumpt;on rate, and the ventl~ation rate were cdkuiated as a function of declining oxygen tension, using the equation for external gas exchange (Fick, 1871); Dejours et ti1., 1970: Dejours, 1972):
where v,v is the volume of water transported in 1:s dry masqhr. t;): the oxygen consumed in ml Cl,& dry mass hr. Ew the ratio of the amount of 0, used to the amount of Q2 atiailable, and cior the inspired oxygen ~on~entra~~on in ml Oz/l. 2. The relation between oxygen consumption and oxygen tension was determined in declining oxygen tension starting from air saturated and oxygen saturated conditions. respectively, in a closed respiration chamber wtth a total volume of 280 ml. The oxygen consumption was monitored witb a Radiometer (TOX 40) oxygen electrode directly inserted into the respiration chamber. The water transport rate through the mantle cavity, designated “perfusion rate” was held constant at 5.6 I&, using a micro centrifugaf pump (volume IO ml) situated at the bottom of the respiration chamber. The outlet of the pump was connected through a rubber tube to the glass tube inserted between the shell valves in the inhalant aperture. The oxygen consumption in declining oxygen tension was determined at different rates of constant water perfusion using the respiration chamber described above. The oxygen consumption was determined as previously described, whereas the perfusion rate was adjusted to di!Terent levels- ?.Y, 5.6, 11.3and I6.4i;hr-with a constant rate in each measuring procedure. The ctenidial function in oxygen uptake, i.e. as a respiratory exchange surface, was examined by monitoring the oxygen consumption in declining oxygen tension in mussels with and without ctenidia, respectively. using the respiration chamber described above. Prior to measurements the posterior adductor muscle was cut. With constant degree of valve opening (angle of 3.5 ‘), the oxygen consumption was mttdsured in declining oxygen tension. Then the ctenidia was cut oRand removed, avoiding any damage of other tissues, and the oxygen consumption measurement repeated with the equal degree of valve opening. The mussel was perfused with a constant rate of 5.6 lihr in both experiments. RESULTS The valve movements of an unFed and u~djsturbed mussel are shown in Fig. 1. The rimes spent open are relatively short, whereas the closed condition seems to pre~ion~~nate. There is a good deal of variation in both the degree of opening and in the time spent closed in a single organism, and variation was also found among different individuals. However, uniformity in the tendency of closing the valves was found among all individuals under laboratory conditions in filtered sea water. The oxygen extraction coefficient (E,), i.e. the ratio of the amount of O2 used to the amount of O2 available, is below 0.1 at high (air saturated) oxygen tensions, increasing slightly with decline in oxygen tension, reaching a value of approx 0.2 at 1%15 mmHg (Fig. 2). Further decline in oxygen tension results in an increase of EW approaching a value of I.0 in oxygen tensions < 5OmmHg. In declining oxygen tension, resulting from the oxygen uptake of the organism, the oxygen consumption f&,) expressed as ml O2 consumed per g dry mass
163
Responses of A4q~rilu.s to declining oxygen tension
Fig. 1. serious rdulis. The relative degree of valve opening as function of time, measured continuously over several days in aerated, filtered sea water. The values 0 and I designate the closed and fully open condition, respectively.
per hr, decreases as seen in Fig. 3. The oxygen consumption describes an hyperbolic relation in declining oxygen tension. That is the rate of oxygen consumption changes more at low concentrations than at higher con~ntrations, and a point is eventually reached where further increase in oxygen tension produces little effect on the oxygen consumption rate. The data for the oxygen consumption in declining oxygen tension was fitted to a hyperbolic model by least squares using a linear transformation of the Michaelis-Menten equation, the Lineweaver-Burk equation : ~Po, = Kn/~‘ln~maxu/Co*) + wm,,, where Vo, is the oxygen consumption rate, K, the oxygen concentration at which the rate is haif maxiand V,,, the mal, co2 the oxygen concentration apparent maximum oxygen consumption rate. All analyses of oxygen consumption in declining oxygen tension in this part of the experiments showed a hyperbolic relation.
Figure 4 shows the relationship between ventilation rate (VW), expressed in terms of volume of water pumped per g dry mass per hr, and declining oxygen tension. The ventilation rate seems rather constant in declining oxygen tension down to 40_50mmHg, whereas further dechne in oxygen tension results in only a slightly reduced ventiiation rate approaching a value of 0.81/g dry weight/hr at oxygen tensions < 5 mmHg. These results are computed from measurements on a single organism, but are qualitatively general for all specimens analyzed. Under conditions of declining oxygen tension from atmospheric air ( - 160 mmHg) and oxygen saturation, (- 760 mmHg) respectively, ~~f~~us e&&s shows a declining oxygen consumption as illustrated for one specimen in Fig. 5(A). The oxygen consumption rate decreases from a near asymptotic level of 160 ~1 OZ/g dry weight/hr at oxygen tensions above 500 mmHg to an oxygen consumption level of 124~1 0,/g dry weight/hr, equal to the level found at 120mmHg
\
l-.. . . ‘--.
‘.-. ~.---*..-._
. s
I
50
i0
100
Oxygen
tension‘P%,
mm
ng)
Fig. 2. ~~rj~us edufis. The oxygen extraction coefficient (E,) as function of declining oxygen tension (mmHg) determined as the ratio of the amount of 0, used to the amount of Oz available.
164
P.
FAMME
and L. H.
KOFOED
100.
0 Oxygen
tension
CPo2.mmHg)
I Fig. 3. Mytilus edulis. The oxygen consumption rate (V. *; ~1 0,/g dry weightihr) as function of declining oxygen tension (mmHg).
when starting from atmospheric air saturated conditions. Below oxygen tensions of I20 mmHg, the oxygen consumption decreases similarly in both cases, irrespective of the different initial oxygen tension. Figure 5(B) shows the Lineweaver-Burk plots of the oxygen consumption curves in declining oxygen tension starting from atmospheric air and oxygen saturated conditions, respectively. The nearly equivaient slopes and y-intercepts of the two plots illustrates the similarity between the apparent maximum oxygen consumption rates and the -I(, values, as listed in Table 1. These data illustrate that the apparent maximum oxygen consumption rate is not significantly different from the measured maximum oxygen consumption rate at hyperoxic conditions. The oxygen consumption in declining oxygen tension at different rates of constant artificial perfusion through the mantle cavity, together with the same unperfused specimen, are shown in Fig. 6(A). Without perfusion the oxygen consumption rate declines slowly with declining oxygen tension down to approx 80mmHg, below which the rate declines sharply to a lower rate at 60mmHg. Further reduction in oxygen tension results in slowly declining oxygen consumption rate. At a low perfusion rate (2.9 l/hr), the oxygen con-
sumption shows a nearly linear correlation to oxygen tension, whereas an increase to a perfusion rate of 5.6I/hr gives a hyperbolic relation between oxygen consumption and declining oxygen tension. Perfusion rates above 5.6 1,hr give smaller changes in the overall oxygen consumption at higher tensions, indicating a level of perfusion rate at which the maximum oxygen consumption capacity is reached in the natural range of oxygen tensions. Increased perfusion rates (above 2.9 l,/hr) through the mantle cavity, therefore. seems to affect the oxygen consumption at all oxygen tensions, and results in a change of the oxygen consumption from a dependent to an independent type. The oxygen consumption increment (relative to the oxygen consumption with a perfusion rate of 2.9 I/hr), is most pronounced at lower oxygen tensions; the increment is as high as 220% with the perfusion rate of 16.4 I/hr. At higher oxygen tensions, the increment is approx 407; at all levels of perfusion rates above 5.6 {/hr. The non-uniform increment in oxygen consumption in declining oxygen tension with increased perfusion rate, is illustrated in the change in K, values, as seen in Fig. 6(B). The slope of the Lineweaver-Burk plots declines with increased perfusion rates, whereas
2.ol------
Fig. 4. M~rilus edulis. The ventilation rate (VW,. 1H,O pumped/g dry weight/hr) as function of declining oxygen tension (mmHg) determined from the equation: VW= V,,/(E,~q,,).
Responses
of Mytilus
to declining
oxygen
tension
165
. -. : 0 -160mmHg 0-O:
100
I
I
200
300
O-760mmHg
1
400
500
Oxygen
Fig. 5A. Mytilus
edulis. The oxygen
consumption
tension
E
)
( PO~,mmHg)
rate (Vo,; plO,/g wet weight/hr) as function of declinto atmospheric air (- 160 mmHg) and and with constant perfusion rate of 5.6 l/hr.
ing oxygen tension (mmHg) in sea water initially equilibrated oxygen
(- 760 mmHg),
respectively,
the y-intercepts are relatively constant, as listed in Table 1. Table 1 shows the values of the rate constants of the Lineweaver-Burk plots, together with the coefficients of determination (r) at the different perfusion rates. The v,,, values seems rather constant although slightly declining with increased perfusion rate. The K, values on the other hand, declines markedly from 132.1 to 49SmmHg on changing the perfusion rate
from 2.9 to 5.6 l/hr. Further increase in perfusion rate from 11.3 to 16.4 l/hr results in only a slight reduction in K, value from 42.3 to 3 1.4 mmHg. All coefficients of determination (r) are above 0.99. The oxygen consumption rates in declining oxygen tension of an organism with intact and excised ctenidia are shown in Fig. 7. With intact ctenidia, the oxygen consumption in declining oxygen tension describes a hyperbolic relation; removing the ctenidia
.I
O-160
.
: O-760
Fig. SB. Myths edwlis. The fitted regression lines for l/Vo2 as a function of l/P,> in sea water initially equilibrated to atmospheric air (5 160 mmHg) and oxygen (- 760 mmHg), respectively. The calculated coefficients of determination (r) and the rate constants (K, and V,,,) are listed in Table 1.
166
P. FAMME and L. H. KOFOED Table i. Mqtilus edulis.Table showing the values for the slope (K,,,/V,,,,,), the rate constants K, and V,,,.,, and the coefficient of determination (r) for linear regression fines, calculated using the transformation of Line~caver-Bllrk of the Michaelis-Menten equation: f/V,, = ~~~~~~~(l/P~~) + I/?“,,,,
Experiment/
%/Vmax
KM (mmHg 1
condition
V max wet
(u102/g
Iw./hr)
Oxygen
tens
O-160
mmHg
0.1697
24.3
143.1
0.991
O-760
mmHg
0.1592
23.7
148.4
0.943
Perfusion
ion
rate
2.9
l/hr
0.1040
132.1
1.27a
0.999
5.6
l/hr
0.0402
49.5
1.23a
0.991
11.3
l/hr
0.0347
42.3
1.22a
0.991
16.4
l/hr
0.0280
31.4
l,lZa
0.994
0.303
25.6
84.5
0.947
0.356
30.1
84.6
0.981
Ctenidia *
a: determined as ml O,,hr and repetition of the experiment under the same conditions, gives the same pattern. The removed ctenidial
are often complicated
tissue represents 3.257; of the total wet weight. DISCUSSION
Experiments in the laboratory on the respiration of time,
unfed mussels during storage and experimental
0 l.*.*
0’
I LN’
J*
r*P
by the fact that mussels close
their valves, or change the degree of valve opening more or less regularly, without any external disturbing factors (Pierce, 1971; Wijsman, 1975; M0hlenberg & RiisgHrd, 1979). Changes in the degree of valve opening are known to interfere with the rate of water transport through the mantle cavity, generally with a decline in water transport rate as valve opening de-
/ ? D
”
unparfused
l
2.9 l/h?
. .
6‘6
i/hr
11.3 l/h@
o 16.4 l/h?
Oxygen
tension
( Po2,mm
ttg)
Fig. 6A. Mytilus edulis. The oxygen consumption rate (V, I; ,uI O,/hr) as function of declining oxygen tension (mmHg). at an unperfused specimen, and at different levels--2.9, 5.6, 11.3, and 16.4 &r-of constant perfusion rates on the same specimen, respectively.
167
Responses of Mytilus to declining oxygen tension
5 l/PO*
(x104)
Fig. 63. Mytilus edulis. The fitted regression lines for l/V,, as a function of l/PO, at an unperfused specimen, and at different levels--2.9, 5.6, 11.3,and 16.4 &k-of constant perfusion rates on the same specimen, respectively. The calculated coefficients of determination (r) and the rate constants (K, and V,,,) are listed in Table 1.
creases (Hopkins, 1933; Jorgensen, 1960; Theede, 1963). The degree of valve opening therefore seems to be as important a factor as e.g. temperature and salinity (Bayne et al., 1976a.b) in relation to the general respiratory responses. Consequently the valve opening was held constant with an angle of 3.5” (for specimens of 70mm length) in all specimens used in our experiments. The water transport rate measured here was approx 1.O- 1.5 l/g dry weight/hr, whereas recent measurements (Riisgard & Mohlenberg, 1979; Mohlenberg & Riisgard, 1979) showed water transport capacities of 5 to 6 l/g dry weight/hr, measured as clearance rate. The introduction of a glass tube between the valves to prevent closure during experiments, probably interferes with the water transport of the organism (Jorgensen, 1943) giving generally lower values than would occur in undisturbed mussel. Reports of water
transport rates in filtered sea water, determined by other methods, are generally lower than those measured as clearance rate, as reviewed by FosterSmith (1974) and Winter (1978). Some of these low rates probably are due to the measuring procedure (J0rgen~n, 1960), but it is also well established that even small amounts of suspended particles in the water induce an increase in the water transport rate (Loosanof & Engle, 1947a,b; Tammes & Dral, 1955; Theede, 1963; Davids, 1964; Thompson & Bayne, 1972; Foster-Smith, 1974; Schulte, 1975). The low water transport rates measured here are thus probab!y due to summation of the effects of both the inserted “glass tube” and the use of filtered sea water. With constant degree of valve opening, the relation between oxygen consumption and declining oxygen tension was found to be hyperbolic in the great majority of specimens examined here. Oxygen uptake approaches an asymptotical maximum oxygen con-
0-m.
- ctanidis
A-A:
+ ctcntdia I
50
100
150
Oxygentension (PO*, mmIi*) Fig. 7. Mytilus edulis. The oxygen consumption rate (Vo,; ~1 02/g wet weight/k) as function of declining oxygen tension (mmHg) of a specimen with intact and excised ctenidia, respectively and with constant perfusion rate of 5.6 I/hr. The calculated coefficients of determination (r) and the rate constants (II, and V,,,,,) are listed in Tabie 1.
168
P. FAMME and L. H. KOFOEII
sumption rate at hyperoxic conditions. The exhaustion of all available oxygen, found in all specimens examined is probably due to the forced valve opening. The hyperbolic relation between oxygen consumption and oxygen tension has previously been described for many invertebrates including marine mussles (Tang, 1933: Bayne, 1971a; 1973b; Taylor & Brand. 1975b; Newell er a[.. 1978). However. Mangum & Van Winkle (1973) found a polynomial (quadratic) model generally more suitable for describing the relation between oxygen consumption and declining oxygen tension in a large number of invertebrates, including ~of~iolus tiemissus. A non-hyperbolic relation was found in only one experiment (see Fig. 6(A), probably due to variation in ventilation rate as oxygen tension declines. The same specimen showed a hyperbolic relation between oxygen consumption and oxygen tension when perfused with a constant rate. The constant rate of water transport therefore seems to be an important factor as concerning the hyperboljc relation between oxygen consumption and declining oxygen tension. The observed high ventilation rate at low oxygen tensions is significantly different from other indirect measurements of water transport rates in declining oxygen tension. Bayne (1971a) found the ventilation rate, measured as clearance rate, to be relatively constant in declining oxygen tensions down to approx 60-gOmmHg, below which the rate dropped off to zero, although oxygen consumption still was present. Thompson & Bayne (1972) proposed that in very dilute suspensions, filtration activity may cease, although the oxygen consumption and presumably the ventilation rate remained unchanged, as also suggested by Bayne et al. (1976a). Such cessation of the filtered water volume relative to the total amount of water transported (= ventilation rate) could be connected to the adjustment of the ostia and/or the position of the lamellae (Foster-Smith, 1974). In an interpretation of the respiratory responses in declining oxygen tension, it therefore is of importance to discriminate between the water transport rate measured as ventilation rate, and as filtration (= clearance) rate. At high oxygen tensions (IZOmmHg), the artificial increases in the level of water perfusion through the mantle cavity of a starved organism, results in pronounced eievated oxygen consumption rate. The oxygen consumption increased approx 4Or,O,,.when the perfusion rate was increased from 2.9 to 5.6 l/hr. At a certain level of perfusion rate (5.6 I/hr), for this specimen, further increases in the rate of perfusion produce only slight increase in the rate of oxygen consumption of the same specimen. The organism used was starved at least 30 days in the laboratory prior to the start of the experimental. This probably explains the dependency of the oxygen consumption to declining oxygen tension in the unperfused situatioil (Fig. 6(A)) (Bayne, 1967: I971a; I973b). The sudden change in the oxygen consumption rate is probably due to a change in the ventilation rate in declining oxygen tension. Thompson & Bayne (1972) and Widdows (1973a) showed that the oxygen consumption increased from a standard rate, associated with minimal filtering activity, to an active rate. as a result of feeding of previously starved specimens. Further they showed, that the almost instantaneous increase in oxygen con-
sumption rate was associated with a greatly enhanced level of activity, i.e. clearance rate. The increase in clearance rate, probably due to increased ventifation rate, seems therefore to produce qualitatively the same enhancement in the rate of oxygen consumption, irrespective of whether the increased water transport rate was due to artificial perfusion or to induced feeding. Similar relations between increased water transport rate and rate of oxygen consumption are reviewed by Bayne rt al. (1976a) associated with the change in other external factors such as temperature and salinity. Measuring on M~‘rifrts &1i.s and ~~l~iiiu.~ ~~i~t~rtziatrus, respectively, Widdows (1973b) and Bayne rf ul. (1975) proposed that the costs of ventilatory activity probably accounts for a significant proportion of the oxygen consumption, whereas Newell & Pye (1970a) relates approx 90’>, of the oxygen consumption to the costs of ciiiary water transport. Use of the perfusion technique to produce different levels of constant water perfusion through the mantle cavity, without increasing the costs of ventilation of the organism, showed that the enhanced oxygen consumption with increased ventilation rate ;s at least partially due to the increased water convection, rather than increased costs of activity. The costs of water transport is not known, but Jorgensen (1975), using an elegant estimation of the quantitative relation between the amount of cells bearing the water transporting cilia and the total body mass. suggested that the oxygen used by the water transporting ciliated cells to constitute only a small part of the total oxygen consumption, probably only about 1’:; (Jorgensen, 1955). Unfortunately, the initial level of perfusion rate (2.9 l/hr) cannot be interpreted as a standard rate of ventilation, but nevertheless using the oxygen consumption at 120 mmHg as an expression of the standard rate of oxygen consumpt~on, the increase in oxygen consu~nption rate following elevated perfusion rate from 2.9 to 5.6I/hr, amounts approximately a factor of 1.4 Widdows (I 973a) showed that the increase in oxygen consumption result; ;g from feeding of previously starved specimens, to amount to about 1.9 times at 160 mmHg. This comparison shows that the increased water transport through the mantle cavity of the organism, in changing from standard to active rate of oxygen consumption, accounts for at least 75’?,, of the total oxygen consumption. Bayne rf ~ri. (1973) supposed the relationship between oxygen consumption and feeding ration to involve two components of costs, the “mechanical costs” associated with feeding, and the “physiological costs” associated with assimilation of the food. Probably a major part of the difference between specimens increasing the rate of oxygen consumption due to feeding and perfusion, respectively, are associated with the latter, the ~‘physiolo~cal costs”. This indicates that a relatively small part of the oxygen consumption increase is due to increased costs of ventilatory activity. In declining oxygen tension, the increment in oxygen consumption due to enhanced levels of constant artificial perfusion rates, showed the most pronounced effect at lower oxygen tensions. Together with the relatively constant apparent maximum oxy-
Responses of Myrilus to declining oxygen tension
gen consumption rate (V,,,), independent of the level of perfusion rate, such changes indicate a shift in the relation between oxygen consumption and declining oxygen tension to a more independent one. Bayne (1967; 1971a) suggested that the KJK, ratio between the rate constants of the linear transformation of Tang (1933) could provide an index of the degree of dependency between oxygen consumption and oxygen tension. Using the analog linear transformation of the Michaelis-Menten equation, the Lineweaver-Burk equation, the I<,,, value is equivalent to the K,/K, ratio. Increasing the perfusion rate, the shift in dcpendency between oxygen consumption and declining oxygen tension is therefore associated with a similar shift in the K, value from high to low values. At perfusion rates above 5.6 ljhr, the change in k’, value is very small and approaches a value of 31 mmHg. Probably a perfusion rate is reached at which further increase in the rate produces little or no effect on the k’, value. The relation between the oxygen consumption dependency index, the k’, value, and the perfusion rate through the mantle cavity implies that the water transport rate is an important factor influencing the dependency of oxygen consumption in declining oxygen tension in Mytilus rdulis. The water transport rate has previously been shown, at least to some extent, to be implicated in the loss of respiratory independency in the bivalves Arctica jsfui7djcu (Taylor & Brand, 1975a,b) and in ~~,~j~~s rdulis (Bayne it al., 1976a). and in the gastropod Crepicfuia ,~r~ljcata (Newell et al., 1978).
The increase in oxygen consumption rate at any oxygen tension with enhanced external convection, as found in Myths edulis, is probably due to the removal of oxygen gradients above the respiring surfaces. The increase in oxygen consumption at oxygen tensions above air saturation relative to the rate at air saturated coIlditions, is due mainly to the increased saturation of the entire gas exchange system (= total body mass). The possible oxygen gradients through the tissues is thereby removed. Oxygen tensions above air saturation did not seem to have any visible influence on Mpilus edwlis, in agreement with the study of Torres & Mangum (1974) on Modiolus demissus.
In ~yr;~us e&&s it is generally accepted with regard to oxygen that the ctenidia are analogous to the gills in teleosts (see Bayne et al.. 3976b), primarily because of the large surface area and good blood supply. If this assumption were correct, removal of the ctenidia, although they only represent approx 3”/; of the total amount of wet weight, should cause a significant reduction in the oxygen consumption rate at any oxygen tension relative to mussels in which the ctenidia are intact. In fact the oxygen consumption rate was unchanged after removal of the ctenidia, provided the same perfusion rate was used. This suggests that the ctenidia in M. edulis may not be comparable to the gills of teleosts in their importance as sites of gas exchanges. The ratio between the area of the lateral faces of the ctenidial filaments to the total body mass estimated by Pelseneer (1935) and Yonge (1947) are 9.0 and 13.5cm2/g wet weight, respectively. The ratio of the total surface area in the mantle cavity to the total
169
body mass is unestimated, but probably this latter ratio is much larger than the former. The open circulation system and the situation of the ctenidia as a shunt on the kidney circulation (Field, 1922; White, 1937) seems to stress the minor role of the ctenidia in respect to gas exchange. The blood returns slowly to the heart, and not necessarily passing the ctenidia. The ctenidial participation in the overall gas exchange therefore seems to be negligible, indicating that the gas exchange takes place at the entire surface exposed to the mantle cavity. The change in oxygen extraction coefficient (E,) in declining oxygen tension is qualitatively similar to previously reported values of Ew for Myrilus rdulis (Bayne, 1971b; Mangum & Burnett, 1975). However, at low oxygen tensions the previously reported maximum values of E,, between 0.3 and 0.6 (see Bayne et al., 1976b) may be due to measurement at oxygen tensions above 10 mmHg, while in the present experiments the Ew approach the value of 1.0 at oxygen tensions below 10 mmHg. The above results, showing the minor role of the ctenidia as a site for gas exchange, seem to indicate that the regulation of the oxygen uptake in declining oxygen tension is independent of the gill perfusion. These data are in contrast to the findings of Bayne (1971b), Mangum & Burnett (1975) and Taylor & Brand (1975a) who suggested that the compensatory responses of clams and ~~r~~~s edulis, respectively, enable the maintenan~ of a relatively stable rate of oxygen uptake to occur within the ctenidia. Suspension feeding in water with a minima1 content of suspended food particles demands the transport of large amounts of water. The hypertrophied ctenidia seems to be the anatomical consequence of this demand, indicating that the primary function of the ctenidia is feeding activity. The respiratory function of the ctenidia therefore is in proportion to the relative weight of ctenidial tissue, representing less than 5”; of the total oxygen consumption. Ackrrowled~e,nerlts-The authors wish to thank Dr C. Barker Jorgensen and Dr R. C. Newell for their critical reading of the manuscript, and to Dr R. Weber for going through the English text. We are also very grateful to the University of Aarhus for provision of facilities at the Marine Biological Laboratory of Aarhus University, Rcrnbjerg, Denmark. Finally we would like to thank Fr. A. Sorensen for pre~dration of the drawings. REFEREYCES BAYUE
B. L. (1967) The respiratory responses of Mytilus perrlcl (L). (Mollusca: Lamellibranchia) to reduced environmental oxygen. Physiol. Zoo/. 40, 307-313. BAYNE B. L. (1971a) Oxygen consumption by three species of lamellibranch molluscs in declining ambient oxygen tension. Camp. &o&em. Physiol. @A, 955-970. BAYNE B. L. (1971b) Ventilation. the heart rate and oxygen uptake by ~~~ti/I~.~ rdufi.s (L) in declining oxygen ten&n. Camp. Biochem. Phvsiol. 4OA, 1065-1085. BAYNE B. L. (1973a).Aspects of metabolism of Mytilus rduIis during starvation. Nefh. J. Sea. Res. 7, 399-410. BAYNE B. L. (1973b) The responses of three species of bivalve molluscs to declining oxygen tension at reduced salinity. Cotp. Biochetn. Physiol. 45A, 793-806. BAYNE B. L., THOMPSON R. J. & WIDWWS
J. (1973)
Some
effects of temperature and food on the rate of oxygen consumption by ~~~fjll(.~edulis L. fn ,!$ecrs qf tempera-
P. FAMMEand L. H. KOFOED
170
ture on Ectothermic Organisms, (Edited by WIESER W.), pp. 1X1-l 93. Springer-Verlag, Berlin. BAKE B. L., BAYNE C. J., CAREFOOT T. C. & THOMPSON R. J. (1975) The physiological ecology of Mytilus caljfornianus Conrad. 1. Aspects of metabolism and energy balance. Oecologia 22, 21 l-228. BABE B. L., THOMPSON R. J. & W~DDOWS J. (1976a) Physiology: 1. In Marine Mussels: Their Ecology und Ph~siology, (Edited by BAYNE B. L.), pp. 121-206. Cambridge University Press. BAY~‘EB. L., WIDI~WS J. & THOMPSON R. J. (I 976b) Physiology: 11. In Marine Mussels: Their Ecology and Physiology, (Edited by BAYNE B. L.), pp. 261-291. Cambridge University Press. DAVIDS C. (1964) The influence of suspensions of microorganisms of different concentrations on the pumping and retention of food by the mussel (Mytilus edulis L.). Nefll. .I. Sea. Res. 2, 233-249. DEJOURS P. (1972) Comparison of gas transport by convection among animals. Resp. Physiol. 14, 96-104. DEJOURS P., GAREY W. F. & RAHN H. (1970) Comparison of ventilatory and circulatory flow rates between animals in various physiological conditions. Resp. Physiol. 9, 10x-1 17. FICK A. (1870) Ueber die Messung des Blutquantums in den Herzventrikel. Sitzher. Physik. Med. Ged. Wu’rzhury XVI. FIELD I. A. (1922) Biology and economic value of the sea mussel Mytilus edulis. Bull. U.S. Bureau Fish. 38, 127-259. FL&EL H. & SCHLIEPER C. (1962) Der Einfluss physikalischer und chemischer Faktoren auf die cilienaktivitlt und Pumprate der Miesmuschel Mytilus edulis. L. Kieler Merre~forschungen. 18, 51-66. FOSTER-SMITH R. L. (1974) A comparative study of the feeding mechanisms of Mytilus edulis L.. Cerastoderma edule CL.), and Venerupis phllastra (Montagu) (Mollusca: Bivalvia). 153 oo. PhD thesis. University of Newcastleon-Tyne. GHIRET~I F. (1966) Respiration. In Physiology qf Mollusca, Vol. II (Edited by WILBUR K. M. & YONGE C. M.) pp. 175-203. Academic Press, London. HAMWI A. & HASKIN H. H. (196X) Oxygen consumption and pumping rates in the hard clam Mercenaria mercenaria: a direct method. Science 163, 823-824. HOPKINS A. E. (1933) Experiments on the feeding behaviour of the oyster Ostreu gigas. J. exp. 2001. 64, 469-494. JORGENSENC. B. (I 943) On the water transport through the gills of bivalves. Acta. physiol. stand. 5, 297-304. _ JORGENSEN C. B. (1952) On the relation between water transport and food requirements in some marine filter feeding invertebrates. Biol. Bull. 103, 356-363. JORGEYS~Y C. B. (1955) Quantitative aspects of filter feeding in invertebrates. Biol. Rev. 30, 391-454. JORGENSEN C. B. (1960) Efficiency of particle retention and rate of water transport in undisturbed lamellibranchs. J. Cons. Int. Ezplor. Mer. 26, 941 16. JORGENSEN C. B. (1966) Tile Biology of Suspension Feeding, 357 pp. Pergamon Press, Oxford. JORGENSEN C. B. (1975) On gill function in the mussel Mytilus edulis L. Ophelia 13, 1X7-232. KROC;H A. (I 94 I) The Comparative Physiology of Respiratory Mechanisms, 142 pp. University of Pennsylvania Press, Philadelphia. LOOSANOFF V. L. & ENGLE J. B. (1947a) Feeding of oysters in relation to density of micro-organisms. Science 105, 26@26 I. LOOSANOFF V. L. & ENGLE J. B. (1947b) Effect of different concentrations of micro-organisms on the feeding of oysters (0. airainica). Bull. U.S. Fish Wildlife Sew. 51, 31-57. MAN&M C.P. & ‘BURNETTL. E. (1975)‘The extraction of oxygen by estuarine invertebrates. In Physiological Ecologv $Estuarine Oryanisms, (Edited by VERNBERG F. J.) a
.
pp. 1477163. University of South Carolina Press, Columbia, South Carolina. MANGUM C. P. & VAN WINKLE W. (1973) Responses of aquatic invertebrates to declining oxygen conditions. Am. 2001. 13, 529-541. MQHLENBERG F. & RIISG~RD H. U. (1979) Filtration rates in 13 species of suspension feeding bivalves of different size measured by a new simple technique. Opheliu 17, 239-246. NEWELL R. C. & PYE V. I. (197Oa) Seasonal changes in the effect of temperature on the oxygen consumption of the winkle Littorina littorea (L.) and the mussel Myfilus edulis (L.). Comp. Eiochem. Physiol. 34, 367-383. NEWELL R. C.. JOHNSON L. G. & KOFOED L. H. (1978) Effects of environmental temperature and hypoxia on the oxygen consumption of the suspension-feeding gastropod Crepidula ,fornicata L. Comp. Biochem. Physiol. 59A, 175-182. OWEN G. (1966) Feeding In Physiology qf Mollusca, (Edited by WILRURK. M. & YONGE C. M.) VOI. II, pp. I 51. Academic Press, London. PELSENEER P. (1935) “Essai d’ethologie zoologique”, pp. 662. Brussels: Acad. Roy. Belg. Classe. Sci. Publ. Fond. Agathon Potter. PIERCE S. K. (1971) Volume regulation and valve movements by marine mussels. Camp. Biochenl. Physiol. 39A, 103-l 17. RIISG~RIIH. U. & M~HLENBERG F. (1979) An improved automatic recording apparatus for determining the filtration rate in Mytilus edulis as a function of size and algal concentration. Mar. Biol. 52, 61-67. SCHULTE E. H. (1975) Influence of algal concentration and temperature on the filtration rate of Mytilus edulis. Mar. Biol. 30, 33 I-34 I, SCHMII)T-NIELSEU K. (I 975) Animal PhysiologqL Adaptation and Enoironment. 699 pp. Cambridge University Press. TAMMESP. M. L. & DRAL A. D. G. (1955) Observations on the straining of suspensions of‘mussels. Arch. NPerl. Zoo/. 11, 87-l 12. TANG P. S. (1933) On the rate of oxygen consumption by tissues and lower organisms as a function of oxygen tension. Q, Rec. Biol. 8, 26&274. TAYLOR A. C. & BRAND A. R. (1975a) A comparative study of the respiratory responses of the bivalve Arctiua is/andica (L) and Mjjtilus edulis L. to declining oxygen tension. Proc. R. Sot. B. 190, 443-456. TAYLOR A. C. & BRAND A. R. (1975b) Effects of hypoxia and body size on the oxygen consumption of the bivalve Arctica islandica (L.). J. esp. mar. BioI. Ecol. 19. 187-196. THEEDE H. (1963) Experimenielle Untersuchungen iiber die Filtrations sleistung der Miesmuschel Mytilus edulis L. Kieler Meere.forschungen. 19, 2&41. THOMPSON R. J. & BAYNE B. L. (1972) Active metabolism associated with feeding in the mussel Mytilus edulis L. J. esp. mar. Biol. Ecol. 8, 191-212. TORRESJ. J. & MANGUM C. P. (I 974) Effects of hypoxia on the survival of benthic marine invertebrates. Comp. Bioc/rem. Physiol. 47A, 17-22. WHITE K. M. (1937) Mytilus. Liverpool Marine Biology Committee Memoirs, no. 31. 177 pp. University of Liverpool Press. Liverpool. WIDDOWS J. (1973a) Effect of temperature and food on the heart beat, ventilation rate and oxygen uptake of Mytilus edulis. Mar. Biol. 20, 269.-76. WIDUOWS J. (1973b) The effects of temperature on the metabolism and activity of Mytilus edulis L. Neth. J. Sea. Rex 7, 3X7-398. WIJSMANT. C. M. (1975) pH fluctuations in Mytilus edulis L. in relation to shell movements under aerobic and anaerobic conditions. Proc. 9th. Europ. mar, biol. Symp., (Edited by BARNES H.), pp. 139 149. Aberdeen University Press.
Responses of WINTER J. E. (1978)
Mytilus
to declining oxygen tension
A review on the knowledge of sus~nsion-feeding in iameilibranchiate bivalves, with special reference to artificiai aquaculture systems. Ayuaculture. 13, l-33.
YONGE C. M. (1947) The pailial organs
171
in the Aspidobranch Gastropoda and their evolution throughout the Mollusca. Phil. Trans. Roy. Sot. 8232, 443.-518.
INTRODLICTION The
ctenidia of suspension feeding bivalves serve a dua1 function in bringing about a ciliary induced water movement through the mantle cavity, and in the clearance of particles from this water, as reviewed by Jorgensen (1966). Beyond these functions the ctenidia have been suggested to take an active part in the oxygen uptake and the regulation of oxygen consumption in declining oxygen tension in Mytilws edulis (Bayne, 1971b; Mangum & Burnett, 1975) and Mercenaria mercenaria (Hamwi & Ha&in, 1968), primarily by regulating the ctenidial perfusion relative to the ventilatory current. Several investigators e.g. Krogh (1941), Ghiretti (I966), Owen (1966), and Jorgensen (1966) have stressed that the respiratory function of the ventilatory current is incidental to the feeding function, and Schmidt-Nielsen (1975) proposed the ctenidia to function only in filter-feeding, whereas the gas exchange is primarily cutaneous. DifficuIt~es in measuring directly the various parameters that are known to be important in effecting oxygen uptake through a “gill-type” of gas exchanger (Dejours, 1972), primarily the parameters of perfusion (Bayne, 1971b), has impeded the understanding of the ctenidial participation in the oxygen uptake by .~~f~~~s e&&s. This is partly due to the nonsimultaneous and indirect determination of other respiratory components, the oxygen extraction coefficient and the ventilation rate. Fhigel & Schlieper (1962) and Theede (1963) suggested that the reduced rate of water transport under conditions of starvation implies a cessation in the “preparedness” of the organism to feeding activity, indicating the water transport during starvation to be mainly of respiratory significance. Under conditions of declining oxygen tension, starvation over a period of at least 30 days is known to
induce dependency between oxygen consumption and oxygen tension (Bayne, 1971a), and a reduction in oxygen consumption as found in M~lti~us edu~is (Bayne et al., 1973) and in ~~ti~us cal~r~ja~us (Bayne et al., 1975). Bayne et al. (1976a) suggested the reduction in oxygen consumption following starvation to be primarily due to reduced costs of ventilatory activity, whereas the change in dependency between oxygen consumption and oxygen tension is connected with a metabolic shift from active to standard metabolism. However, Jorgensen (1952; 1960) found in different bivalves, including Mytilus edulis, that the rate of water transport could be kept constant under conditions when the rate of oxygen uptake were reduced. The main purpose of the present study has been to investigate the participation of the ventilatory current and ctenidia in oxygen uptake by Mytilus edulis in declining oxygen tension, by means of simultaneous measurement of the components of the external gas exchange. These components are the oxygen tension, the oxygen extraction coefficient, the oxygen consumption, and the ventilation rate. MATERIALS AND METHODS
The experiments of part I were carried out at the Marine Biological Laboratory of Aarhus University, Ronbjerg, Denmark, in late August, 1978. Specimens of Mytilus edulis, with a mean length of 7 cm, were collected from the upper intertidal zone in the vicinity of the laboratory. The mussels were stored at least 2 days prior to labaratory recordings in an aquarium with running, aerated sea water. The water temperature varied between 16.0 and lS.O”C throughout the experimental period, whereas the salinity was constant at 24”:,,. The mussels were unfed throughout the experimental period, and kept with constant degree of valve opening (with an angle of 3.5”) by means of a glass
161
I62
P. F.AMM~ and L. H. KOFOEI>
tube inserted between the shell valves at the inhafant aperture. The valves were held in position by means of an anteriorly placed rubber band. The experiments of part II were carried oui at the Biological laboratory of Odense University, Denmark, in the late autumn and winter. 197X/79.The mussels (mean length of 7cm) were collected at Kertmge Nor. Denmark, and stored in large containers with aerated sea water at least 14 days before used in experiments. The acciimation and experimental temperature was IWC and the salinity was 17.I’:,<,.The mussels were unfed throughout the storage and experiment& period, and without any determinated degree of valve opening during the storage, whereas during experiments the mussels were kept with constant degre of valve opening as above. Variation in the degree of valve opening during storage was examined at several mussels under laboratory conditions. The musseis were tixed at the one shell valve at the bottom of an aquarium, whereas the other sheil valve was connected to an electrical transducer (linear potentiometer]. and the output monitored on a multicb~rli~ei recorder ~Fhjl~jps PM 98.13). The practlwi work consisted of two parts: 1. To measure the oxygen tension of the exhalant water, an outlet from the mantle cavity was made by drilling a 2.1 mm hole in the one shell valve near the exhalant aperture. taking care not to damage the underlying mantle face. A rubber tube with an approximatei~ equal diameter was pushed into the hole, and through it was inserted a hypodermic needle, with an outer diameter of 1.t mm. making a tight fit. The hypodermic needle was carefully pushed 3 mm into the mantle cavity, making a tiny hole in the mantle tissue. The mounting procedure was partially adapted from Wijsman (1975), and studies on survival with needle Inserted under normal laboratory conditions showed no change in the behaviour or survival time. in relation to undisturbed mussels under the same conditions. Prior to measurements. the mussel was plitced in a respiration chamber, and the outlet rrom the mantle cavity mounted to a “butyl” rubber tube passing air proof out of the respi~tion chamber. This tube was seriatly connected to an oxygen electrode chamber and peristaltic pump, and then passed back into the respiration chamber. The water volume outside the respiration chamber was Sml. giving an entire volume of the measuring system of 100ml. The mussel was left undisturbed for at least I hr in the open, aerated respiration chamber prior to expcrimental start. At the start OF the experiment the respiration chamber was closed, avoiding any air bubbles, and the peristaltic pump started with a constant Row of 275 mtlhr. The small suction of water from the exhalant part of the mantle cavity did not seem to affect the mussel. in that the activity and position of the mantle edges of the inhalant and exhalant apertures showed no response when the peristaltic pump was shut on and off several times with short intervals. The water in the respiration chamber was well stirred by means of an magnetic stirrer in the bottom of the chamber, separated from the musselby a small piece of glass. The temperature of the entire apparatus was controfled by immersion into running sea water. The oxygen tension of the water in the respiration chamber was continuously monitored with a Radiometer (TOX 40) oxygen electrode directly inserted into the respiration chamber, whereas the oxygen tension of the exhalant water was monitored in the etectrode chamber outside the respiration chamber with a similar electrode, using for both electrodes a Radiometer (TOX JO) ox~transmitter system. The electrode signals were cuntinuously recorded on B mu~ticb~l~e~ recorder (Phillips PiLf 9833).
From the oxygen concentration of mspired and expired water, the oxygen extraction coefficient (Dejours, 1977). the oxygen ~onsumpt;on rate, and the ventl~ation rate were cdkuiated as a function of declining oxygen tension, using the equation for external gas exchange (Fick, 1871); Dejours et ti1., 1970: Dejours, 1972):
where v,v is the volume of water transported in 1:s dry masqhr. t;): the oxygen consumed in ml Cl,& dry mass hr. Ew the ratio of the amount of 0, used to the amount of Q2 atiailable, and cior the inspired oxygen ~on~entra~~on in ml Oz/l. 2. The relation between oxygen consumption and oxygen tension was determined in declining oxygen tension starting from air saturated and oxygen saturated conditions. respectively, in a closed respiration chamber wtth a total volume of 280 ml. The oxygen consumption was monitored witb a Radiometer (TOX 40) oxygen electrode directly inserted into the respiration chamber. The water transport rate through the mantle cavity, designated “perfusion rate” was held constant at 5.6 I&, using a micro centrifugaf pump (volume IO ml) situated at the bottom of the respiration chamber. The outlet of the pump was connected through a rubber tube to the glass tube inserted between the shell valves in the inhalant aperture. The oxygen consumption in declining oxygen tension was determined at different rates of constant water perfusion using the respiration chamber described above. The oxygen consumption was determined as previously described, whereas the perfusion rate was adjusted to di!Terent levels- ?.Y, 5.6, 11.3and I6.4i;hr-with a constant rate in each measuring procedure. The ctenidial function in oxygen uptake, i.e. as a respiratory exchange surface, was examined by monitoring the oxygen consumption in declining oxygen tension in mussels with and without ctenidia, respectively. using the respiration chamber described above. Prior to measurements the posterior adductor muscle was cut. With constant degree of valve opening (angle of 3.5 ‘), the oxygen consumption was mttdsured in declining oxygen tension. Then the ctenidia was cut oRand removed, avoiding any damage of other tissues, and the oxygen consumption measurement repeated with the equal degree of valve opening. The mussel was perfused with a constant rate of 5.6 lihr in both experiments. RESULTS The valve movements of an unFed and u~djsturbed mussel are shown in Fig. 1. The rimes spent open are relatively short, whereas the closed condition seems to pre~ion~~nate. There is a good deal of variation in both the degree of opening and in the time spent closed in a single organism, and variation was also found among different individuals. However, uniformity in the tendency of closing the valves was found among all individuals under laboratory conditions in filtered sea water. The oxygen extraction coefficient (E,), i.e. the ratio of the amount of O2 used to the amount of O2 available, is below 0.1 at high (air saturated) oxygen tensions, increasing slightly with decline in oxygen tension, reaching a value of approx 0.2 at 1%15 mmHg (Fig. 2). Further decline in oxygen tension results in an increase of EW approaching a value of I.0 in oxygen tensions < 5OmmHg. In declining oxygen tension, resulting from the oxygen uptake of the organism, the oxygen consumption f&,) expressed as ml O2 consumed per g dry mass
163
Responses of A4q~rilu.s to declining oxygen tension
Fig. 1. serious rdulis. The relative degree of valve opening as function of time, measured continuously over several days in aerated, filtered sea water. The values 0 and I designate the closed and fully open condition, respectively.
per hr, decreases as seen in Fig. 3. The oxygen consumption describes an hyperbolic relation in declining oxygen tension. That is the rate of oxygen consumption changes more at low concentrations than at higher con~ntrations, and a point is eventually reached where further increase in oxygen tension produces little effect on the oxygen consumption rate. The data for the oxygen consumption in declining oxygen tension was fitted to a hyperbolic model by least squares using a linear transformation of the Michaelis-Menten equation, the Lineweaver-Burk equation : ~Po, = Kn/~‘ln~maxu/Co*) + wm,,, where Vo, is the oxygen consumption rate, K, the oxygen concentration at which the rate is haif maxiand V,,, the mal, co2 the oxygen concentration apparent maximum oxygen consumption rate. All analyses of oxygen consumption in declining oxygen tension in this part of the experiments showed a hyperbolic relation.
Figure 4 shows the relationship between ventilation rate (VW), expressed in terms of volume of water pumped per g dry mass per hr, and declining oxygen tension. The ventilation rate seems rather constant in declining oxygen tension down to 40_50mmHg, whereas further dechne in oxygen tension results in only a slightly reduced ventiiation rate approaching a value of 0.81/g dry weight/hr at oxygen tensions < 5 mmHg. These results are computed from measurements on a single organism, but are qualitatively general for all specimens analyzed. Under conditions of declining oxygen tension from atmospheric air ( - 160 mmHg) and oxygen saturation, (- 760 mmHg) respectively, ~~f~~us e&&s shows a declining oxygen consumption as illustrated for one specimen in Fig. 5(A). The oxygen consumption rate decreases from a near asymptotic level of 160 ~1 OZ/g dry weight/hr at oxygen tensions above 500 mmHg to an oxygen consumption level of 124~1 0,/g dry weight/hr, equal to the level found at 120mmHg
\
l-.. . . ‘--.
‘.-. ~.---*..-._
. s
I
50
i0
100
Oxygen
tension‘P%,
mm
ng)
Fig. 2. ~~rj~us edufis. The oxygen extraction coefficient (E,) as function of declining oxygen tension (mmHg) determined as the ratio of the amount of 0, used to the amount of Oz available.
164
P.
FAMME
and L. H.
KOFOED
100.
0 Oxygen
tension
CPo2.mmHg)
I Fig. 3. Mytilus edulis. The oxygen consumption rate (V. *; ~1 0,/g dry weightihr) as function of declining oxygen tension (mmHg).
when starting from atmospheric air saturated conditions. Below oxygen tensions of I20 mmHg, the oxygen consumption decreases similarly in both cases, irrespective of the different initial oxygen tension. Figure 5(B) shows the Lineweaver-Burk plots of the oxygen consumption curves in declining oxygen tension starting from atmospheric air and oxygen saturated conditions, respectively. The nearly equivaient slopes and y-intercepts of the two plots illustrates the similarity between the apparent maximum oxygen consumption rates and the -I(, values, as listed in Table 1. These data illustrate that the apparent maximum oxygen consumption rate is not significantly different from the measured maximum oxygen consumption rate at hyperoxic conditions. The oxygen consumption in declining oxygen tension at different rates of constant artificial perfusion through the mantle cavity, together with the same unperfused specimen, are shown in Fig. 6(A). Without perfusion the oxygen consumption rate declines slowly with declining oxygen tension down to approx 80mmHg, below which the rate declines sharply to a lower rate at 60mmHg. Further reduction in oxygen tension results in slowly declining oxygen consumption rate. At a low perfusion rate (2.9 l/hr), the oxygen con-
sumption shows a nearly linear correlation to oxygen tension, whereas an increase to a perfusion rate of 5.6I/hr gives a hyperbolic relation between oxygen consumption and declining oxygen tension. Perfusion rates above 5.6 1,hr give smaller changes in the overall oxygen consumption at higher tensions, indicating a level of perfusion rate at which the maximum oxygen consumption capacity is reached in the natural range of oxygen tensions. Increased perfusion rates (above 2.9 l,/hr) through the mantle cavity, therefore. seems to affect the oxygen consumption at all oxygen tensions, and results in a change of the oxygen consumption from a dependent to an independent type. The oxygen consumption increment (relative to the oxygen consumption with a perfusion rate of 2.9 I/hr), is most pronounced at lower oxygen tensions; the increment is as high as 220% with the perfusion rate of 16.4 I/hr. At higher oxygen tensions, the increment is approx 407; at all levels of perfusion rates above 5.6 {/hr. The non-uniform increment in oxygen consumption in declining oxygen tension with increased perfusion rate, is illustrated in the change in K, values, as seen in Fig. 6(B). The slope of the Lineweaver-Burk plots declines with increased perfusion rates, whereas
2.ol------
Fig. 4. M~rilus edulis. The ventilation rate (VW,. 1H,O pumped/g dry weight/hr) as function of declining oxygen tension (mmHg) determined from the equation: VW= V,,/(E,~q,,).
Responses
of Mytilus
to declining
oxygen
tension
165
. -. : 0 -160mmHg 0-O:
100
I
I
200
300
O-760mmHg
1
400
500
Oxygen
Fig. 5A. Mytilus
edulis. The oxygen
consumption
tension
E
)
( PO~,mmHg)
rate (Vo,; plO,/g wet weight/hr) as function of declinto atmospheric air (- 160 mmHg) and and with constant perfusion rate of 5.6 l/hr.
ing oxygen tension (mmHg) in sea water initially equilibrated oxygen
(- 760 mmHg),
respectively,
the y-intercepts are relatively constant, as listed in Table 1. Table 1 shows the values of the rate constants of the Lineweaver-Burk plots, together with the coefficients of determination (r) at the different perfusion rates. The v,,, values seems rather constant although slightly declining with increased perfusion rate. The K, values on the other hand, declines markedly from 132.1 to 49SmmHg on changing the perfusion rate
from 2.9 to 5.6 l/hr. Further increase in perfusion rate from 11.3 to 16.4 l/hr results in only a slight reduction in K, value from 42.3 to 3 1.4 mmHg. All coefficients of determination (r) are above 0.99. The oxygen consumption rates in declining oxygen tension of an organism with intact and excised ctenidia are shown in Fig. 7. With intact ctenidia, the oxygen consumption in declining oxygen tension describes a hyperbolic relation; removing the ctenidia
.I
O-160
.
: O-760
Fig. SB. Myths edwlis. The fitted regression lines for l/Vo2 as a function of l/P,> in sea water initially equilibrated to atmospheric air (5 160 mmHg) and oxygen (- 760 mmHg), respectively. The calculated coefficients of determination (r) and the rate constants (K, and V,,,) are listed in Table 1.
166
P. FAMME and L. H. KOFOED Table i. Mqtilus edulis.Table showing the values for the slope (K,,,/V,,,,,), the rate constants K, and V,,,.,, and the coefficient of determination (r) for linear regression fines, calculated using the transformation of Line~caver-Bllrk of the Michaelis-Menten equation: f/V,, = ~~~~~~~(l/P~~) + I/?“,,,,
Experiment/
%/Vmax
KM (mmHg 1
condition
V max wet
(u102/g
Iw./hr)
Oxygen
tens
O-160
mmHg
0.1697
24.3
143.1
0.991
O-760
mmHg
0.1592
23.7
148.4
0.943
Perfusion
ion
rate
2.9
l/hr
0.1040
132.1
1.27a
0.999
5.6
l/hr
0.0402
49.5
1.23a
0.991
11.3
l/hr
0.0347
42.3
1.22a
0.991
16.4
l/hr
0.0280
31.4
l,lZa
0.994
0.303
25.6
84.5
0.947
0.356
30.1
84.6
0.981
Ctenidia *
a: determined as ml O,,hr and repetition of the experiment under the same conditions, gives the same pattern. The removed ctenidial
are often complicated
tissue represents 3.257; of the total wet weight. DISCUSSION
Experiments in the laboratory on the respiration of time,
unfed mussels during storage and experimental
0 l.*.*
0’
I LN’
J*
r*P
by the fact that mussels close
their valves, or change the degree of valve opening more or less regularly, without any external disturbing factors (Pierce, 1971; Wijsman, 1975; M0hlenberg & RiisgHrd, 1979). Changes in the degree of valve opening are known to interfere with the rate of water transport through the mantle cavity, generally with a decline in water transport rate as valve opening de-
/ ? D
”
unparfused
l
2.9 l/h?
. .
6‘6
i/hr
11.3 l/h@
o 16.4 l/h?
Oxygen
tension
( Po2,mm
ttg)
Fig. 6A. Mytilus edulis. The oxygen consumption rate (V, I; ,uI O,/hr) as function of declining oxygen tension (mmHg). at an unperfused specimen, and at different levels--2.9, 5.6, 11.3, and 16.4 &r-of constant perfusion rates on the same specimen, respectively.
167
Responses of Mytilus to declining oxygen tension
5 l/PO*
(x104)
Fig. 63. Mytilus edulis. The fitted regression lines for l/V,, as a function of l/PO, at an unperfused specimen, and at different levels--2.9, 5.6, 11.3,and 16.4 &k-of constant perfusion rates on the same specimen, respectively. The calculated coefficients of determination (r) and the rate constants (K, and V,,,) are listed in Table 1.
creases (Hopkins, 1933; Jorgensen, 1960; Theede, 1963). The degree of valve opening therefore seems to be as important a factor as e.g. temperature and salinity (Bayne et al., 1976a.b) in relation to the general respiratory responses. Consequently the valve opening was held constant with an angle of 3.5” (for specimens of 70mm length) in all specimens used in our experiments. The water transport rate measured here was approx 1.O- 1.5 l/g dry weight/hr, whereas recent measurements (Riisgard & Mohlenberg, 1979; Mohlenberg & Riisgard, 1979) showed water transport capacities of 5 to 6 l/g dry weight/hr, measured as clearance rate. The introduction of a glass tube between the valves to prevent closure during experiments, probably interferes with the water transport of the organism (Jorgensen, 1943) giving generally lower values than would occur in undisturbed mussel. Reports of water
transport rates in filtered sea water, determined by other methods, are generally lower than those measured as clearance rate, as reviewed by FosterSmith (1974) and Winter (1978). Some of these low rates probably are due to the measuring procedure (J0rgen~n, 1960), but it is also well established that even small amounts of suspended particles in the water induce an increase in the water transport rate (Loosanof & Engle, 1947a,b; Tammes & Dral, 1955; Theede, 1963; Davids, 1964; Thompson & Bayne, 1972; Foster-Smith, 1974; Schulte, 1975). The low water transport rates measured here are thus probab!y due to summation of the effects of both the inserted “glass tube” and the use of filtered sea water. With constant degree of valve opening, the relation between oxygen consumption and declining oxygen tension was found to be hyperbolic in the great majority of specimens examined here. Oxygen uptake approaches an asymptotical maximum oxygen con-
0-m.
- ctanidis
A-A:
+ ctcntdia I
50
100
150
Oxygentension (PO*, mmIi*) Fig. 7. Mytilus edulis. The oxygen consumption rate (Vo,; ~1 02/g wet weight/k) as function of declining oxygen tension (mmHg) of a specimen with intact and excised ctenidia, respectively and with constant perfusion rate of 5.6 I/hr. The calculated coefficients of determination (r) and the rate constants (II, and V,,,,,) are listed in Tabie 1.
168
P. FAMME and L. H. KOFOEII
sumption rate at hyperoxic conditions. The exhaustion of all available oxygen, found in all specimens examined is probably due to the forced valve opening. The hyperbolic relation between oxygen consumption and oxygen tension has previously been described for many invertebrates including marine mussles (Tang, 1933: Bayne, 1971a; 1973b; Taylor & Brand. 1975b; Newell er a[.. 1978). However. Mangum & Van Winkle (1973) found a polynomial (quadratic) model generally more suitable for describing the relation between oxygen consumption and declining oxygen tension in a large number of invertebrates, including ~of~iolus tiemissus. A non-hyperbolic relation was found in only one experiment (see Fig. 6(A), probably due to variation in ventilation rate as oxygen tension declines. The same specimen showed a hyperbolic relation between oxygen consumption and oxygen tension when perfused with a constant rate. The constant rate of water transport therefore seems to be an important factor as concerning the hyperboljc relation between oxygen consumption and declining oxygen tension. The observed high ventilation rate at low oxygen tensions is significantly different from other indirect measurements of water transport rates in declining oxygen tension. Bayne (1971a) found the ventilation rate, measured as clearance rate, to be relatively constant in declining oxygen tensions down to approx 60-gOmmHg, below which the rate dropped off to zero, although oxygen consumption still was present. Thompson & Bayne (1972) proposed that in very dilute suspensions, filtration activity may cease, although the oxygen consumption and presumably the ventilation rate remained unchanged, as also suggested by Bayne et al. (1976a). Such cessation of the filtered water volume relative to the total amount of water transported (= ventilation rate) could be connected to the adjustment of the ostia and/or the position of the lamellae (Foster-Smith, 1974). In an interpretation of the respiratory responses in declining oxygen tension, it therefore is of importance to discriminate between the water transport rate measured as ventilation rate, and as filtration (= clearance) rate. At high oxygen tensions (IZOmmHg), the artificial increases in the level of water perfusion through the mantle cavity of a starved organism, results in pronounced eievated oxygen consumption rate. The oxygen consumption increased approx 4Or,O,,.when the perfusion rate was increased from 2.9 to 5.6 l/hr. At a certain level of perfusion rate (5.6 I/hr), for this specimen, further increases in the rate of perfusion produce only slight increase in the rate of oxygen consumption of the same specimen. The organism used was starved at least 30 days in the laboratory prior to the start of the experimental. This probably explains the dependency of the oxygen consumption to declining oxygen tension in the unperfused situatioil (Fig. 6(A)) (Bayne, 1967: I971a; I973b). The sudden change in the oxygen consumption rate is probably due to a change in the ventilation rate in declining oxygen tension. Thompson & Bayne (1972) and Widdows (1973a) showed that the oxygen consumption increased from a standard rate, associated with minimal filtering activity, to an active rate. as a result of feeding of previously starved specimens. Further they showed, that the almost instantaneous increase in oxygen con-
sumption rate was associated with a greatly enhanced level of activity, i.e. clearance rate. The increase in clearance rate, probably due to increased ventifation rate, seems therefore to produce qualitatively the same enhancement in the rate of oxygen consumption, irrespective of whether the increased water transport rate was due to artificial perfusion or to induced feeding. Similar relations between increased water transport rate and rate of oxygen consumption are reviewed by Bayne rt al. (1976a) associated with the change in other external factors such as temperature and salinity. Measuring on M~‘rifrts &1i.s and ~~l~iiiu.~ ~~i~t~rtziatrus, respectively, Widdows (1973b) and Bayne rf ul. (1975) proposed that the costs of ventilatory activity probably accounts for a significant proportion of the oxygen consumption, whereas Newell & Pye (1970a) relates approx 90’>, of the oxygen consumption to the costs of ciiiary water transport. Use of the perfusion technique to produce different levels of constant water perfusion through the mantle cavity, without increasing the costs of ventilation of the organism, showed that the enhanced oxygen consumption with increased ventilation rate ;s at least partially due to the increased water convection, rather than increased costs of activity. The costs of water transport is not known, but Jorgensen (1975), using an elegant estimation of the quantitative relation between the amount of cells bearing the water transporting cilia and the total body mass. suggested that the oxygen used by the water transporting ciliated cells to constitute only a small part of the total oxygen consumption, probably only about 1’:; (Jorgensen, 1955). Unfortunately, the initial level of perfusion rate (2.9 l/hr) cannot be interpreted as a standard rate of ventilation, but nevertheless using the oxygen consumption at 120 mmHg as an expression of the standard rate of oxygen consumpt~on, the increase in oxygen consu~nption rate following elevated perfusion rate from 2.9 to 5.6I/hr, amounts approximately a factor of 1.4 Widdows (I 973a) showed that the increase in oxygen consumption result; ;g from feeding of previously starved specimens, to amount to about 1.9 times at 160 mmHg. This comparison shows that the increased water transport through the mantle cavity of the organism, in changing from standard to active rate of oxygen consumption, accounts for at least 75’?,, of the total oxygen consumption. Bayne rf ~ri. (1973) supposed the relationship between oxygen consumption and feeding ration to involve two components of costs, the “mechanical costs” associated with feeding, and the “physiological costs” associated with assimilation of the food. Probably a major part of the difference between specimens increasing the rate of oxygen consumption due to feeding and perfusion, respectively, are associated with the latter, the ~‘physiolo~cal costs”. This indicates that a relatively small part of the oxygen consumption increase is due to increased costs of ventilatory activity. In declining oxygen tension, the increment in oxygen consumption due to enhanced levels of constant artificial perfusion rates, showed the most pronounced effect at lower oxygen tensions. Together with the relatively constant apparent maximum oxy-
Responses of Myrilus to declining oxygen tension
gen consumption rate (V,,,), independent of the level of perfusion rate, such changes indicate a shift in the relation between oxygen consumption and declining oxygen tension to a more independent one. Bayne (1967; 1971a) suggested that the KJK, ratio between the rate constants of the linear transformation of Tang (1933) could provide an index of the degree of dependency between oxygen consumption and oxygen tension. Using the analog linear transformation of the Michaelis-Menten equation, the Lineweaver-Burk equation, the I<,,, value is equivalent to the K,/K, ratio. Increasing the perfusion rate, the shift in dcpendency between oxygen consumption and declining oxygen tension is therefore associated with a similar shift in the K, value from high to low values. At perfusion rates above 5.6 ljhr, the change in k’, value is very small and approaches a value of 31 mmHg. Probably a perfusion rate is reached at which further increase in the rate produces little or no effect on the k’, value. The relation between the oxygen consumption dependency index, the k’, value, and the perfusion rate through the mantle cavity implies that the water transport rate is an important factor influencing the dependency of oxygen consumption in declining oxygen tension in Mytilus rdulis. The water transport rate has previously been shown, at least to some extent, to be implicated in the loss of respiratory independency in the bivalves Arctica jsfui7djcu (Taylor & Brand, 1975a,b) and in ~~,~j~~s rdulis (Bayne it al., 1976a). and in the gastropod Crepicfuia ,~r~ljcata (Newell et al., 1978).
The increase in oxygen consumption rate at any oxygen tension with enhanced external convection, as found in Myths edulis, is probably due to the removal of oxygen gradients above the respiring surfaces. The increase in oxygen consumption at oxygen tensions above air saturation relative to the rate at air saturated coIlditions, is due mainly to the increased saturation of the entire gas exchange system (= total body mass). The possible oxygen gradients through the tissues is thereby removed. Oxygen tensions above air saturation did not seem to have any visible influence on Mpilus edwlis, in agreement with the study of Torres & Mangum (1974) on Modiolus demissus.
In ~yr;~us e&&s it is generally accepted with regard to oxygen that the ctenidia are analogous to the gills in teleosts (see Bayne et al.. 3976b), primarily because of the large surface area and good blood supply. If this assumption were correct, removal of the ctenidia, although they only represent approx 3”/; of the total amount of wet weight, should cause a significant reduction in the oxygen consumption rate at any oxygen tension relative to mussels in which the ctenidia are intact. In fact the oxygen consumption rate was unchanged after removal of the ctenidia, provided the same perfusion rate was used. This suggests that the ctenidia in M. edulis may not be comparable to the gills of teleosts in their importance as sites of gas exchanges. The ratio between the area of the lateral faces of the ctenidial filaments to the total body mass estimated by Pelseneer (1935) and Yonge (1947) are 9.0 and 13.5cm2/g wet weight, respectively. The ratio of the total surface area in the mantle cavity to the total
169
body mass is unestimated, but probably this latter ratio is much larger than the former. The open circulation system and the situation of the ctenidia as a shunt on the kidney circulation (Field, 1922; White, 1937) seems to stress the minor role of the ctenidia in respect to gas exchange. The blood returns slowly to the heart, and not necessarily passing the ctenidia. The ctenidial participation in the overall gas exchange therefore seems to be negligible, indicating that the gas exchange takes place at the entire surface exposed to the mantle cavity. The change in oxygen extraction coefficient (E,) in declining oxygen tension is qualitatively similar to previously reported values of Ew for Myrilus rdulis (Bayne, 1971b; Mangum & Burnett, 1975). However, at low oxygen tensions the previously reported maximum values of E,, between 0.3 and 0.6 (see Bayne et al., 1976b) may be due to measurement at oxygen tensions above 10 mmHg, while in the present experiments the Ew approach the value of 1.0 at oxygen tensions below 10 mmHg. The above results, showing the minor role of the ctenidia as a site for gas exchange, seem to indicate that the regulation of the oxygen uptake in declining oxygen tension is independent of the gill perfusion. These data are in contrast to the findings of Bayne (1971b), Mangum & Burnett (1975) and Taylor & Brand (1975a) who suggested that the compensatory responses of clams and ~~r~~~s edulis, respectively, enable the maintenan~ of a relatively stable rate of oxygen uptake to occur within the ctenidia. Suspension feeding in water with a minima1 content of suspended food particles demands the transport of large amounts of water. The hypertrophied ctenidia seems to be the anatomical consequence of this demand, indicating that the primary function of the ctenidia is feeding activity. The respiratory function of the ctenidia therefore is in proportion to the relative weight of ctenidial tissue, representing less than 5”; of the total oxygen consumption. Ackrrowled~e,nerlts-The authors wish to thank Dr C. Barker Jorgensen and Dr R. C. Newell for their critical reading of the manuscript, and to Dr R. Weber for going through the English text. We are also very grateful to the University of Aarhus for provision of facilities at the Marine Biological Laboratory of Aarhus University, Rcrnbjerg, Denmark. Finally we would like to thank Fr. A. Sorensen for pre~dration of the drawings. REFEREYCES BAYUE
B. L. (1967) The respiratory responses of Mytilus perrlcl (L). (Mollusca: Lamellibranchia) to reduced environmental oxygen. Physiol. Zoo/. 40, 307-313. BAYNE B. L. (1971a) Oxygen consumption by three species of lamellibranch molluscs in declining ambient oxygen tension. Camp. &o&em. Physiol. @A, 955-970. BAYNE B. L. (1971b) Ventilation. the heart rate and oxygen uptake by ~~~ti/I~.~ rdufi.s (L) in declining oxygen ten&n. Camp. Biochem. Phvsiol. 4OA, 1065-1085. BAYNE B. L. (1973a).Aspects of metabolism of Mytilus rduIis during starvation. Nefh. J. Sea. Res. 7, 399-410. BAYNE B. L. (1973b) The responses of three species of bivalve molluscs to declining oxygen tension at reduced salinity. Cotp. Biochetn. Physiol. 45A, 793-806. BAYNE B. L., THOMPSON R. J. & WIDWWS
J. (1973)
Some
effects of temperature and food on the rate of oxygen consumption by ~~~fjll(.~edulis L. fn ,!$ecrs qf tempera-
P. FAMMEand L. H. KOFOED
170
ture on Ectothermic Organisms, (Edited by WIESER W.), pp. 1X1-l 93. Springer-Verlag, Berlin. BAKE B. L., BAYNE C. J., CAREFOOT T. C. & THOMPSON R. J. (1975) The physiological ecology of Mytilus caljfornianus Conrad. 1. Aspects of metabolism and energy balance. Oecologia 22, 21 l-228. BABE B. L., THOMPSON R. J. & W~DDOWS J. (1976a) Physiology: 1. In Marine Mussels: Their Ecology und Ph~siology, (Edited by BAYNE B. L.), pp. 121-206. Cambridge University Press. BAY~‘EB. L., WIDI~WS J. & THOMPSON R. J. (I 976b) Physiology: 11. In Marine Mussels: Their Ecology and Physiology, (Edited by BAYNE B. L.), pp. 261-291. Cambridge University Press. DAVIDS C. (1964) The influence of suspensions of microorganisms of different concentrations on the pumping and retention of food by the mussel (Mytilus edulis L.). Nefll. .I. Sea. Res. 2, 233-249. DEJOURS P. (1972) Comparison of gas transport by convection among animals. Resp. Physiol. 14, 96-104. DEJOURS P., GAREY W. F. & RAHN H. (1970) Comparison of ventilatory and circulatory flow rates between animals in various physiological conditions. Resp. Physiol. 9, 10x-1 17. FICK A. (1870) Ueber die Messung des Blutquantums in den Herzventrikel. Sitzher. Physik. Med. Ged. Wu’rzhury XVI. FIELD I. A. (1922) Biology and economic value of the sea mussel Mytilus edulis. Bull. U.S. Bureau Fish. 38, 127-259. FL&EL H. & SCHLIEPER C. (1962) Der Einfluss physikalischer und chemischer Faktoren auf die cilienaktivitlt und Pumprate der Miesmuschel Mytilus edulis. L. Kieler Merre~forschungen. 18, 51-66. FOSTER-SMITH R. L. (1974) A comparative study of the feeding mechanisms of Mytilus edulis L.. Cerastoderma edule CL.), and Venerupis phllastra (Montagu) (Mollusca: Bivalvia). 153 oo. PhD thesis. University of Newcastleon-Tyne. GHIRET~I F. (1966) Respiration. In Physiology qf Mollusca, Vol. II (Edited by WILBUR K. M. & YONGE C. M.) pp. 175-203. Academic Press, London. HAMWI A. & HASKIN H. H. (196X) Oxygen consumption and pumping rates in the hard clam Mercenaria mercenaria: a direct method. Science 163, 823-824. HOPKINS A. E. (1933) Experiments on the feeding behaviour of the oyster Ostreu gigas. J. exp. 2001. 64, 469-494. JORGENSENC. B. (I 943) On the water transport through the gills of bivalves. Acta. physiol. stand. 5, 297-304. _ JORGENSEN C. B. (1952) On the relation between water transport and food requirements in some marine filter feeding invertebrates. Biol. Bull. 103, 356-363. JORGEYS~Y C. B. (1955) Quantitative aspects of filter feeding in invertebrates. Biol. Rev. 30, 391-454. JORGENSEN C. B. (1960) Efficiency of particle retention and rate of water transport in undisturbed lamellibranchs. J. Cons. Int. Ezplor. Mer. 26, 941 16. JORGENSEN C. B. (1966) Tile Biology of Suspension Feeding, 357 pp. Pergamon Press, Oxford. JORGENSEN C. B. (1975) On gill function in the mussel Mytilus edulis L. Ophelia 13, 1X7-232. KROC;H A. (I 94 I) The Comparative Physiology of Respiratory Mechanisms, 142 pp. University of Pennsylvania Press, Philadelphia. LOOSANOFF V. L. & ENGLE J. B. (1947a) Feeding of oysters in relation to density of micro-organisms. Science 105, 26@26 I. LOOSANOFF V. L. & ENGLE J. B. (1947b) Effect of different concentrations of micro-organisms on the feeding of oysters (0. airainica). Bull. U.S. Fish Wildlife Sew. 51, 31-57. MAN&M C.P. & ‘BURNETTL. E. (1975)‘The extraction of oxygen by estuarine invertebrates. In Physiological Ecologv $Estuarine Oryanisms, (Edited by VERNBERG F. J.) a
.
pp. 1477163. University of South Carolina Press, Columbia, South Carolina. MANGUM C. P. & VAN WINKLE W. (1973) Responses of aquatic invertebrates to declining oxygen conditions. Am. 2001. 13, 529-541. MQHLENBERG F. & RIISG~RD H. U. (1979) Filtration rates in 13 species of suspension feeding bivalves of different size measured by a new simple technique. Opheliu 17, 239-246. NEWELL R. C. & PYE V. I. (197Oa) Seasonal changes in the effect of temperature on the oxygen consumption of the winkle Littorina littorea (L.) and the mussel Myfilus edulis (L.). Comp. Eiochem. Physiol. 34, 367-383. NEWELL R. C.. JOHNSON L. G. & KOFOED L. H. (1978) Effects of environmental temperature and hypoxia on the oxygen consumption of the suspension-feeding gastropod Crepidula ,fornicata L. Comp. Biochem. Physiol. 59A, 175-182. OWEN G. (1966) Feeding In Physiology qf Mollusca, (Edited by WILRURK. M. & YONGE C. M.) VOI. II, pp. I 51. Academic Press, London. PELSENEER P. (1935) “Essai d’ethologie zoologique”, pp. 662. Brussels: Acad. Roy. Belg. Classe. Sci. Publ. Fond. Agathon Potter. PIERCE S. K. (1971) Volume regulation and valve movements by marine mussels. Camp. Biochenl. Physiol. 39A, 103-l 17. RIISG~RIIH. U. & M~HLENBERG F. (1979) An improved automatic recording apparatus for determining the filtration rate in Mytilus edulis as a function of size and algal concentration. Mar. Biol. 52, 61-67. SCHULTE E. H. (1975) Influence of algal concentration and temperature on the filtration rate of Mytilus edulis. Mar. Biol. 30, 33 I-34 I, SCHMII)T-NIELSEU K. (I 975) Animal PhysiologqL Adaptation and Enoironment. 699 pp. Cambridge University Press. TAMMESP. M. L. & DRAL A. D. G. (1955) Observations on the straining of suspensions of‘mussels. Arch. NPerl. Zoo/. 11, 87-l 12. TANG P. S. (1933) On the rate of oxygen consumption by tissues and lower organisms as a function of oxygen tension. Q, Rec. Biol. 8, 26&274. TAYLOR A. C. & BRAND A. R. (1975a) A comparative study of the respiratory responses of the bivalve Arctiua is/andica (L) and Mjjtilus edulis L. to declining oxygen tension. Proc. R. Sot. B. 190, 443-456. TAYLOR A. C. & BRAND A. R. (1975b) Effects of hypoxia and body size on the oxygen consumption of the bivalve Arctica islandica (L.). J. esp. mar. BioI. Ecol. 19. 187-196. THEEDE H. (1963) Experimenielle Untersuchungen iiber die Filtrations sleistung der Miesmuschel Mytilus edulis L. Kieler Meere.forschungen. 19, 2&41. THOMPSON R. J. & BAYNE B. L. (1972) Active metabolism associated with feeding in the mussel Mytilus edulis L. J. esp. mar. Biol. Ecol. 8, 191-212. TORRESJ. J. & MANGUM C. P. (I 974) Effects of hypoxia on the survival of benthic marine invertebrates. Comp. Bioc/rem. Physiol. 47A, 17-22. WHITE K. M. (1937) Mytilus. Liverpool Marine Biology Committee Memoirs, no. 31. 177 pp. University of Liverpool Press. Liverpool. WIDDOWS J. (1973a) Effect of temperature and food on the heart beat, ventilation rate and oxygen uptake of Mytilus edulis. Mar. Biol. 20, 269.-76. WIDUOWS J. (1973b) The effects of temperature on the metabolism and activity of Mytilus edulis L. Neth. J. Sea. Rex 7, 3X7-398. WIJSMANT. C. M. (1975) pH fluctuations in Mytilus edulis L. in relation to shell movements under aerobic and anaerobic conditions. Proc. 9th. Europ. mar, biol. Symp., (Edited by BARNES H.), pp. 139 149. Aberdeen University Press.
Responses of WINTER J. E. (1978)
Mytilus
to declining oxygen tension
A review on the knowledge of sus~nsion-feeding in iameilibranchiate bivalves, with special reference to artificiai aquaculture systems. Ayuaculture. 13, l-33.
YONGE C. M. (1947) The pailial organs
171
in the Aspidobranch Gastropoda and their evolution throughout the Mollusca. Phil. Trans. Roy. Sot. 8232, 443.-518.