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Effects of temperature and salinity on oxygen consumption and nitrogen excretion in Thais (Nucella) lapillus (L.)
J. Exp. Mar. Biol. Ecol., 1982, Vol. 58, pp. l-17
Elsevier Biomedical Press
EFFECTS OXYGEN
OF TEMPERATURE
CONSUMPTION
AND SALINITY
AND NITROGEN
THAIS (NUCELLA) LAPILLUS
ON
EXCRETION
IN
(L.)
W. B. STICKLE’ and B. L. BAYNE Institute for Marine Environmental
Research, Prospect
‘Place. The Hoe, Plymouth
PLI 3DH, U.K.
Abstract: The 2-wk TLm of stepwise-acclimated Thais lapillus (L.) ( >20 mm long) was 14.2-16.2% salinity (S) at 5, 10, 15, and 20 “C. The same TLm occurred at 10 “C after direct transfer of snails to the final salinity but stepwise-acclimated small snails ( ~20 mm) tolerated a significantly lower salinity (12.7% S). Oxygen consumption rates (PO,) tit the allometric equation fi0, = a. W”.60*‘.O’. Salinity and temperature had a significant effect on @O,, which was highest at 30% S and depressed at 17.5% S and at 5 “C. Ammonia excretion rates fit the allometric equation tNH$ = a . W”.6’* ‘.05. Both salinity and temperature affected VNH$. Ammonia excretion was significantly lower at 17.5 % S than at higher salinities at 10, 15, and 20°C but did not vary as a function of salinity at 5°C. Primary amines were lost from snails under all conditions without any obvious relationship with temperature or salinity. Primary-amine loss, expressed as a percentage of PNH;, was significantly higher at 17.5 56, S than at higher salinities. Oxygen : nitrogen ratios ranged from 4.2-15.6, indicating protein was the primary metabolic substrate, and were highest at 15 “C and lowest at 5 “C. Snails withstood 89 days starvation without mortality at 10°C. Oxygen consumption of snails declined by 28% during starvation due to a 37% decline in dry weight; consequently, weight-specific respiration rate increased by 17%. The intercept (a) for the fi0, allometric equations did not change during starvation. Ammonia excretion increased during starvation, and primary-amine loss increased until Day 21, then declined. Oxygen : nitrogen ratios declined from 14 to 8, indicating an increased catabolism of protein during starvation.
Water temperature and salinity vary tidally and seasonally within estuaries. Synergistic interactions between these variables can be expected to regulate the distribution and activity of many estuarine invertebrates. Muricid gastropods are important predators of mussels, oysters, and barnacles in the food webs of marine hard substrata (Carriker, 1955; Connell, 1961, 1970, 1972; Menge, 1976; Menge & Sutherland, 1976; Paine, 1966). Many species of muricid gastropods do not, however, survive in low salinity regions of estuaries. For example, the low-salinity limit of Thais lapillus in the Severn Estuary is 20-28 &, S (Boyden et al., 1977) while that of T. haemastoma is z 15 “/, S (St. Amant, 1938, 1957). T. haemastoma will, however, tolerate 7.5% S at 10, 20, and 30°C for at least a month following laboratory acclimation (Garton & Stickle, 1980). ’ Permanent address: Zoology and Physiology Department, LA 70803, U.S.A.
Louisiana State University, Baton Rouge,
0022-0981/82/OOOO-OOOO/$O2.75 0 1982 Elsevier Biomedical Press
2
W. B. STICKLE
AND
B. L. BAYNE
The rate of oxygen consumption of acclimated muricid gdstropods varies with temperature, salinity, and time since their last meal. Little acclimation of oxygen consumption occurs with seasonal changes in water tempe~ture in T. lap~~il4.~ (Bayne & Scullard, 1978) or T. lamdlosrc: (Stickle, 1973). The rate of oxygen consumption of T. lamehsa is significantly lower at 15 x0 S than at 20, 30, or 407$, S (Stickle, 1970) whereas the rate of oxygen consumption of T. Izcrrmastoma is significantly lower at 10 yWS than at 20 or 30% S (Findley PI al., 1978). Bayne & Sculiard (1978) found the rate of oxygen consumption of T. /~~~j~l~,s to be high during feeding but to decline during 18 days of starvation. in contrast. the rate of oxygen consumption by T. lamellosa remained constant or increased during 53 days (Stickle & Duerr, 1970) and 91 days starvation (Stickle, 1971). The metabolic substrata catabolized by T. Iumellosu during starvation varied with the stage of the reproductive cycle, but protein was always the major nutrient utilized (Stickle & Duerr, 1970; Stickle. 1971). Ammonia excretion is also modified by temperature, salinity. and starvation in T. lamellosa but no data exist for T. lapillw. Stickle (1970) found the NH,* excretion rate of T. lamellosa to be higher at 9 than at 15 “C. Snails used for the 9 “C experiment had, however, starved for over 2 months while in reproductive aggregations before the NH; excretion rates were determined. Stickle (1970) also found that the NH: excretion rate of T. Iameihsa acclimated to 15 %, S was significantly lower than that of snails acclimated to 20, 30, or 40’&, S. The net flux of primary amines (free amino acids) has not been determined for any species of gastropod at environmentally realistic ambient concentrations of amino acids. Several methods exist for the estimation of the relative amounts of carbohydrate, lipid, and protein catabolized by animals. The calculation of the respiratory quotient (RQ) is notoriously unreliable in animals which possess calcareous skeletons because carbon dioxide, produced via respiration, may be fixed in the calcareous shell material. Conover & Corner (1968) first used the ratio of oxygen consumed to nitrogen excreted in atomic equivalents (0 : N ratio) as an indication of biochemical substrate metabotized. A high 0: N ratio is indicative of carbohydrate and/or lipid catdbo1ism while a ratio as low as 4-8 indicates that only protein is being catabolized (Conover & Corner, 1968; Mayzaud, 1973). The present study was undertaken to determine the en‘ects of temperature, salinity, and starvation on the survival, rate of oxygen consumption, ammonia and primary-amine excretion, and 0: N ratios of the muricid gastropod, T. la~ii~~ (L.). Two other studies will report on the effects of temperature and salinity on the Scope for Growth, growth efficiencies, feeding cycle, lysosomai fragility, and correlation of stress indices in 7: lapillus.
RESPIRATION AND NITROGEN EXCRETION BY THAI.5 MATERIAL
AND METHODS
T. ~~~~1~~s were collected at low tide from a rocky shore at Bovisand, South Devon, England. Collections were made during September, 1978, and during January and February, 1979, at an ambient salinity of 34.5 x0. Water temperature was within 3 “C of the respective experimental temperatures of 5, 10, 15, and 20°C. Snails were stepwise-acclimated to test salinities of 10, 12.5, 15, 17.5, 20, 25, 30, and 350/, at a rate of 2 y&,S per day. The 35 y&,S treatments were inadvertently omitted at 15 and 20 “C. Snails were provided mussels (Mytifus eMis L.) for prey, except during the fasting experiment and during the time it took to determine rates of oxygen consumption and nitrogen excretion. SURVIVAL EXPERIMENTS Survival of Thais lapillus ( >20 mm long) was determined on groups of 25-40 snails per salinity after 2-wk exposure to the test salinities. Survival was also determined after 5-wk exposure to the test salinities at 5 “C because of the longer time it took snails to die. In addition, snails ( r20 mm long) were directly transferred to all test salinities at 10 *C to compare results with those for stepwise-acclimated snails. Finally, survival of juvenile snails ( < 20 mm long) was determined at 10 “C after stepwise acclimation. EXPERIMENTAL DESIGN Three series of experiments were carried out to determine the effects of tempersalinity, and starvation on physiological rates in T. lupillus. (1) After determining survival, we measured the feeding rate of 30 snails, representative of the size range characteristic of the Bovisand population, for 3 wk at 17.5 and 30 “/, Sand at 5, 10, 15, and 20 “C. The oxygen consumption and nitrogen excretion rates were then determined for each experimental group of snails which will be identified as the “predator-prey” series. (2) In a second set of experiments, 10 snails of standard length (23-28 mm) were used in feeding rate experiments at 17.5, 20, 25, and 30”/, S and at 5, 10, 15, and 20 “C for 3 wk. Feeding rates were also determined for standard length snails at 35% S and 5 and 10°C. Oxygen consumption and nitrogen excretion rates were determined for each group of snails before and after the 3-wk feeding rate experiment. (3) Finally, the rates of oxygen consumption and nitrogen excretion were determined for 12 snails on 0, 21, 49, and 89 days of fasting at 10 “C and 30 y&,S. Estimated dry weight before the feeding rate experiments and during the fasting experiment was obtained for each snail by prediction of the initial weight from total length. Separate dry weight to length regression lines were constructed for each sex from a group of snails collected at the same time as the experimental snails. Females were significantly heavier per unit length than males. Predicted
ature,
W. B. STICKLE
-I
AND B. L. BAYNE
weight at any time was obtained
by correcting
the appropriate decimal end of the experiment.
fraction
of dry weight change
OXYGEN
EXPERIMENTS
The
CONSUMPTION
rate
of oxygen
consumption
the predicted
of snails
was
initial
between
determined
dry weight by
collection
with
and the
a Gilson
Differential Respirometer equipped with 1 IO-ml reaction flasks. 40 ml of Milliporetiltered and air-saturated sea water of the appropriate salinity was added to each reaction flask, and flasks were shaken at the slowest rate. Snails crawled about and remained submerged throughout all experiments. Oxygen consumption rates were corrected to N.T.P. as ~1 0, .h -‘. AMMONIA
AND PRIMARY-AMINE
EXCRETION
EXPERIMENTS
Snails were placed into 100 ml Millipore-filtered and air-saturated sea water of the appropriate salinity for 4 h. Control beakers containing sea water from the same batch, but with no animals, were incubated for the same time. Excretion rates were determined as the difference between the ammonia and primary-amine content in the beakers containing snails and the control beakers. Plastic restrainers kept snails below the surface of the water. Ammonia levels were determined by a modification (Grasshoff & Johannsen, 1972) of the method of Sol6rzano (1969) with ammonium sulphate used as the standard. Primary-amine (free amino acid) levels were determined by the fluorescamine method of North (1975) using leucine as a standard. OXYGEN
: NITROGEN
RATIOS
The 0: N ratio was determined in two ways after conversion of the oxygen consumption. ammonia and primary-amine excretion rates to atomic equivalents. 0 : N ratios were calculated on the basis of ammonia the basis of the sum of ammonia and primary-amine STATISTICAL
excretion excretion
rates alone and on rates.
ANALYSIS
Survival data were analysed by the method of Finney (1971) and presented as the TLm + the 95% fiducial limits. Significant differences between individual TLm values are given as regions of non-overlap of the 95J?,; fiducial limits. In the initial data analysis of oxygen consumption, ammonia and primary-amine excretion, the relationship between physiological rates and body weight were described for each predator-prey experimental condition by the allometric equation : Y = uX”, where Y = the physiological rate, X = the dry flesh weight (in mg) and h and log,,,a are the slope and intercept of the log,,, Y/log,,,X regression, respectively. The individual regression lines for each rate function were then compared by analysis of covariance
RESPIRATION
AND NITROGEN EXCRETION
BY THAZS
5
to test whether the slopes were significantly different. Because signi~~nt differences in slopes, a common regression coefficient that was then used to re-calculate the intercepts of all three sets Analysis of variance was used to test variation among treatments Multiple Range Test was used to identify significant differences treatments.
there were no was -eakulated of experiments. and Duncan’s between those
RESULTS SURVIVAL AS A FUNCTION
OF TEMPERATURE
AND SALINITY
T. i~p~l~u~( >20 mm long) tolerated a slightly lower salinity at 5 (5 wk), 10, and 20 “C than at 15 “C (Fig. 1). The 2-wk TLm was si~i~~antly lower than the
TLm
30
IO
5
TEMPERATURE
I5
20
(“Cl
Fig. 1. Survival of large ( >20 mm long) This fap~~Zusas a function of temperature and salinity is given as median tolerance limits (TLm) f the 95% confidence interval: unmarked data, 2-wk TLm of stepwise acclimated snails; n , 5-wk TLm at 5°C; DT, 2-wk TLm of snails directly transferred from 34.5ym S to the test salinity; J, 2-wk TLm of juvenile snails which were ~20 mm long.
5-wk TLm at 5 “C. There was no signi~cant difference in the TLm for large ( >20 mm long) T. ~up~~~us stepwise acclimated or directly transferred to experimental salinities at 10 “C. Small snails ( ~20 mm) tolerated lower salinity (12.7%) than large snails ( >20 mm; 15.1 X s) at 10 “C. OXYGEN CONSUMPTION
EXPERIMENTS
Oxygen consumption data from the predator-prey experiments were subjected to analysis of covariance to test for statistical differences in slopes and intercepts
W. H. STIC‘KLF.
h
AND
13.L. BAYNtr.
when oxygen consumption (~1 0: h ’ = PO?) was regressed on dry flesh wt in mg ‘fW) after logarithmic transformation. Differences between slopes were not significant (P < 0.05). The regression exponent (h) was 0.60 + 0.07.
Antifogs
of the intercept values (u) + st and Q,,, t’or o.~ygccnconsumption
feedine-rate experiments
ol‘ Uwj
IqiNw
used in the
of ~2 usin p a common value kitr h = 0.60 in the equation: log,,, @‘(I2 = log,+z + 0.60 loglo I+‘. where pa, is given in 1.11 0, h ’ and Ci’ IS given in mg dry flesh wt
OlOvaluesare given
after re-calculation
for the temperature
intervals 5 10 f’. ------._-__ Temperature
5
I0
I5
If) IS ‘C. and I5 31°C‘: N.D.. ...____-_
:
no data.
(‘C)
10
“_-_...__. 5 IO
IO I
f5 -70
Salinity inrercepts ‘i
CX)
-
Yltl
17.5 10
0.37 * 0. I.5 0.58 f 0. IS
0.7.: & 0.16 0.96 + 0. lb
f.O2z1:0.15 0.K rt 0. I7
0 78 * 0.14 l.l2~0.5
: ‘J 2.-
2.0 (I 7
‘5 30 i’;
0.49 + 0.15
1.01 + 0.16
I.10 $I 0.17
1.04+(r.lh
1.2
I .06f 0.17 lb
l.lO&.
l.f6+0.17
21
I2 I I
0.51+ 0.14 0.48 i 0. f 5
0.90 + 0.
0.17
KD N.D. -_.--.-~~_-.-.~__.~
3s -.____...
&.I>. __-
0.6
I .9 0.9 I.1 N.D.
Intercept values (u) of log PO, regressed on log dry wt for the feeding experiment snails were re-calculated with a common slope of 0.60. Q,,, values were calculated from these data (Table I). Quantitative agreement between the predator-prey and feeding-rate data sets for the same treatment was very good. 1:‘02 intercept values were highest at 15 and 20 “C and 30x, S while snails exhibited lowest intercept values for PO, at 5 “C (Duncan’s Multiple Range Test). High Q,,, values between 5 and 10°C coupled with low intercept values indicate suppression of oxygen consumption at 5 “C. The oxygen consumption rate of dog-whelks was well acclimated to temperature between 10 and 20 “C. To test for the effects of temperature, salinity, and time on snail @OZ. the data sets were analysed by first calculating, for each measurement in each data set, PO, . W -’ 6oand then calculating the mean value of each set, The mean 60, . W m” represents the rate of oxygen consumption per unit of metabolic body size, thus excluding variance between sets that is due to differences in body weight. Mean PO, . W -‘M values were then analysed in a three-way anatysis of variance with the variables being temperature, salinity, and time (before and after the 3-wk feeding experiment). Temperature (P < 0.001) and salinity (P < 0.001) had a significant effect on GO2 W -““, but there was no effect due to time. Therefore, the initial and final PO, . W -““’ for each data set were averaged to give mean oxygen consumption per unit of metabolic body size for each saIinjty--tem~erat~e combination. Duncan’s Multiple Range Test indicated that the salinity effect on cO1_. W -“bo is due to a depression of oxygen consumption at 17.5 “/w S at 5, IO,
RESPIRATION
AND
and 20 “C and the temperature all salinities (Fig. 2).
2.5
P b
NITROGEN
7
BY THAIS
EXCRETION
effect is due to depressed PO, . W -“.60 at 5 “C and
5ec
P!OW
50
2.0 2 6 ‘3 -ei
\ 1.5
9
+M-+-+
0.5
i
i
+
500
20 5 d
I++-+-+\
1.0
+’
15
‘3
. IO 4-9 I 5m II
L
15
20
25
30
35
b
I5
20
L
I
I
I
I
25
30
35
I5
20
1
1
25
30
J
’
’
’
I5
20
25
30
SALINITY (%d Fig. 2. Average oxygen consumption and ammonia excretion data for Thais lapiNus are presented as to,. W-o.6oand pNH$ W-o.6’ which represent the rates per unit of metabolic size and exclude variance between data sets due to differences in body weight: data are presented as the mean f I SE.
AMMONIA
EXCRETION
EXPERIMENTS
Predator-prey data sets of ammonia excretion rate were used to test for the interaction between temperature, salinity, and body size. Ammonia excretion rate, PM NH: . h-’ = PNH:, was regressed on dry flesh wt, in mg ( W), after logarithmic transformation, for each temperature-salinity combination and then subjected to analysis of covariance. Differences between slopes were not significant (P >0.05) but differences between intercepts were (P < 0.001). The pooled exponent was 0.61 & 0.05 so the regression equation becomes pNH,+ = a . W”.61*‘.O’. Intercept values (a) were re-calculated with a common slope of 0.61. Agreement between the predator-prey groups and average rate from the initial and final data sets from the feeding-rate experiments was good but not as close as occurred with the PO, data. Re-calculated intercept and Q,, values from the feeding rate experiments are given in Table II. Re-calculated intercept values of pNH,+ do not vary as a function of salinity at 5 “C but are significantly lower at 17.5 X than at higher
8
W. B. STICKLE AND B. L. BAYNE
salinities at 10, 15, and 20 “C according to Duncan’s Multiple Range Test. Values for Qt, were low between each temperature tested in this study.
Antilogs of the intercept values (u) &SE and Q,,, for NH; excretion of 7‘hcti.s lupdlus used in the feeding-rate experiments after re-calculation of a using the common value for h = 0.61 in the equation: W..13given in mg dry i0gloti~ri4+ = 10g,,a + 0.61 logluWwhere ~‘NH,+ isgiveninnMNH$.h-‘and flesh wt; Qlo values are given for the temperature intervals S- 10°C. IO- IS’<‘. and 15%20°C; N.D., no data. ‘Temperature (“C)
Salinity (%o)
17.5 20 25 30 35
5 _~~~~~~_~._ ._.
I0
15
20
5 IO -.
Intercepts li
..__“._,___~~~_~~~~__._. _... ..~ ~_~_....--.._ 1.88 f 0.1 I 1.84*0.12
I .Y3f 0.I I I .93 + 0.11 1.89 + 0.11
1.88* 0.12 2.27 +_0.12 2.34 + 0.12 2.27 f 0. I3 2.22 + 0.12
2.14~O.lI 2.24 + 0.13 2.39f0.13 2.25 rf:0.13 N.D.
2.24 f 0.11 2.36 + 0.11 2.37 t 0.13 2.44Ito.13 N.D.
IU- IS
1%20
._..
911, ~~ _ ~~ ._.. ..__ ._.__ I 00 1.23 t.47 1.58 1.3s
1.30 0.99 I .04 O.98 N.D.
1.10
1.05 0.98 I.18 N.D.
To test for the effects of temperature, salinity, and time on @‘NH:, the rate of ammonia excretion per unit metabolic size (PNH; . W-““I) was calculated for each observation. The average value in each data set was calculated to exclude variance between data sets due to differences in body weight. Mean 6’NH: +Wy-Ohl rates were then analysed in a three-way analysis of variance as was done with GO,. Temperature (P < 0.001) and salinity (P (0.01) had a significant effect on ~NH; . W -‘A’ but there was no effect due to time (P >0.05). Taking the average of the initial and final PNH; W -“A’ values for each data set, overall average rates per unit metabolic size show the salinity effect to be due to an enhancement of ammonia excretion at 25 & S and 15 “C as well as depressed ammonia excretion at 1’7.50/, S and 10°C (Fig. 2). There is no detectable salinity effect at the temperature extremes of 5 and 20°C. The temperature effect is due to a large increase in FNH: between 5 and 10 “C (Duncan’s Multiple Range Test). PRIMARY-AMINE
EXCRETION EXPERIMENTS
Predator-prey data sets of primary-amine excretion rates by 7: lapillus were used to test for differences due to temperature, saiinity, and snail dry weight. In the pooled regression of amine excretion and body size, the F value (1,152 d.f.) is only 5.8 1 and the correlation coefficient is 0.19. The biological relevance of the regression is, therefore, marginal. Therefore, all the data from the feeding rate experiments were pooled and presented as nM primary amines excreted per g dry-flesh wt and as a percentage of the PNH: excretion for the same snails (Table III).
RESPIRATION
AND NITROGEN
9
EXCRETION BY THAIS
No significant differences existed between the initial and the final rates of primary-amine loss from snails, so average values are presented for all treatments (Table III). ~i~i~~nt variation existed in the average rates of primary-amine excretion (P <0.0.5), but this was due largely to temperature-salinity interactions. III
TABLE
Average primary-amine loss rate in nM . g -’ ’ h-I and expressed as a percentage (in parentheses) of NH: excretion rate for Thnis~apjllus during the 3-wk feeding cycte experiment. Temperature (“C) Salinity (L) 17.5 20 2s 30
S 316 104 109 363
(41) (13) (18) (30)
10 121 236 144 61
(25) (16) (11) (7)
15 221 173 326 111
(19) (20) (33) (20)
20 321 226 246 124
(30) (23) (13) (17)
Duncan’s Multiple Range Test indicated that the excretion rate at 5 “C and 30 %,,S was si~i~cantly higher than at all other treatments, whereas the loss rate at 10°C and 300/, S was significantly lower than at ail other salinities. When primary-amine loss rates were expressed as a percentage of 9NH,’ from the same snails, only 3 of 18 paired t-test comparisons showed a significant difference between the initial and final data sets for each treatment. Therefore, average values were calculated for each treatment. Salinity exerted a significant effect on this relationship (P < 0.05) but temperature did not. Duncan’s Multiple Range Test showed primary-amine excretion rates to comprise a higher percentage of ammonia excretion at 17.5 y&,S than at all other salinities. OXYGEN : NITROGEN RATIOS
Predator-prey data sets of the 0 : N ratios were analysed for temperature, salinity, and interaction effects with dry weight. No significant treatment or treatment-dry weight interaction occurred in the analysis of covariance for data sets that utilized only ammonia as nitrogenous excreta or those that summed ammonia and primaryamine excretion rates. Therefore, data from the feeding rate experiments were analysed for differences in 0: N ratio between the initial and final determination of oxygen consumption and nitrogen excretion. No significant differences existed between the paired data sets for each treatment, so the initial and final 0 : N ratios were averaged for each snail before mean 0 : N ratios were determined for each treatment (Table IV). With regard to data sets using ammonia as the only nitrogen excreta, significant variation existed between treatments (P < 0.0001) which was due to a temperature effect (P < 0.0001) and temperature-salinity interaction (P < 0.005). Duncan’s
W. B. STIC‘KLt
RhD
8. L.. HAYNE
RESPIRATION
AND NITROGEN
EXCRETION
BY THAIS
11
Multiple Range Test shows the 0 : N ratios to be significantly higher at 15, than at 10 and 20 “C, whereas those at 5 “C are significantly lower; identical statistical results occurred when ammonia and primary-amine excreta were combined, but the 0 : N ratio for a given treatment was then l-2 units lower. FASTING
STUDY
Oxygen consumption and nitrogen excretion rates were dete~ined on Days 0, 21,49, and 89 of fasting (Table V). The oxygen consumption rate declined by 28% when expressed on a per snail basis but increased by 17% when expressed on a g dry-tissue wt basis during the 89-day fasting period. Tissue weight had declined by 37% during the fasting period. Ammonia excretion rate increased by 15% when expressed on a per-snail basis and by 81% when expressed on a dry-tissue wt basis. Primary-amine excretion increased from the control level to maximum values on Day 21 and then returned to the control level by Day 891when expressed on both a per-snail and a per dry-wt basis. The 0 : N ratio indicated that T. lupillus primarily catabolized protein during fasting and its reliance on protein increased with the fasting period up to 49 days and did not change by Day 89.
DISCUSSION
T. iapilhs tolerated lower salinity in our study (14.2-16.2 % S) than the 22.8 “/ S minimum reported by Fischer (1928) or 20-25 “I, S found in the summer by Okland (1933). Temperatures between 5 and 20°C did not influence the salinity tolerance of the dogwhelk, whose geographical range is from the 0°C winter isotherm, in the proximity of the northern limit of its distribution, to 35-35.5 “C (Gowanloch, 1927). Boyden ef al. (1977) found the dogwhelk in salinities as low as 20-28 ‘&,in the Severn Estuary. A species distribution in nature may be limited, however, by biotic as well as abiotic factors interacting with salinity and temperature. Juvenile dogwhelks tolerated a significantly lower salinity (12.7(2/,) than large snails (15.1X) at 10 “C. However, little biological significance can be assigned to a 2.4& S difference in salinity tolerance. Salinity and temperature affected the J?O: of T. iapillus. At 17.5& 6’0, was depressed but at 20-30s S, PO, did not change. There appears to be little effect of salinity on the oxygen consumption rate of Ttiais spp. at salinities above their low-salinity tolerance limit. T. lumellosa, acclimated to 15x, S, respired at a significantly lower rate than those acclimated to 20, 30, or 40x,, S (Stickle, 1970). T. ~aemast~ma respired at a significantly lower rate at 10 %, S than at 20 or 30 “I, S; their low-salinity tolerance limit is lower than 5% S (Findley ef al., 1978). The rate of oxygen consumption by the dogwhelk was depressed at all salinities
-
21 49 89
0
Day of starvation
Effects of logI CO, regression regression
v
229 f 207 * 187k t45rt
~-
(mg)
P weight
15 14 13 13
-
32 30 27 23
_...._~~_
0.77 0.79 0,74 0.73
k 0.13 k 0.14 + 0.14 10.13
0, consumption (~1 0, .I.____ __log N Snail 138 147 142 161
”
g
‘h -’ )
234 275 305 268
. __-._
Snail
(nM
.~
1.52 k 0.12 1.86 kO.17 1.92+0.17 1.90 rt 0.16
. . . _.-
log a
NH: N excretion _~~~ __. .___ .I
1022 1329 i631 1848
g
’ h -’ )
-_-___
13+ 88 & 63 + 8+
._
._
e 43F 5 430 * I84 360 + 114 SO + 88
PA excretion
1 32 17 II
Snail
-. _.-
14.0 11.7 7.9 8.0
F + + f
fdti0
0:N
1.9 2.2 1.2 0.7
starvation on Tkti~ iupilh at 10°C and 3Oy&, S, values for oxygen consumption rates are calculated from the regression equation = loga + O.&J log U’. where l”O, is given as .uI O? h - ’ and U’ = dry flesh wt in mg; values for NH; excretion rates are calculated from the equation log,,, VNH: = logu t 0.61 log W where c.NH; is given as nM NH’ 4 h -’ : values for primary-amine excretion rates did not fit a equation and are given as nM primary amines. snail _ ’ zkSEand nM PA ‘g-’ ‘h-’ + SE; 0: N ratios are given as the ratio in atomic equivaients of oxygen consumed to NH,f -nitrogen excreted; n = 12.
TAHLF
RESPIRATION
AND NITROGEN
EXCRETION
BY THAIS
13
at 5 “C as shown by low intercept a values and high Q,,, values between 5 and 10 “C. Little predation on Mytilus edulis occurred at 5 “C; in fact, the Scope for Growth (see Bayne, 1975) of the snails was negative throughout the 17.5-350/, salinity range (unpubl. obs.). Bayne & Scullard (1978) also found a winter depression in oxygen consumption by Thais lapillus and concluded that the depression was due to the combined effects of reduced temperature and time since last meal (5-8 days). Snails living at 5 “C are more sensitive to an increase in water temperature at 5-10 “C (Q,” values are 3.7-10.3), than snails living in the rest of their normal temperature range where Q,, values vary from 0.9 to 1.7. Energy losses are minimized as a result of depressed oxygen consumption at low temperature. Bayne & Scullard (1978) point out that the dogwhelk is prepared to respond rapidly to a rise in temperature in the spring; it is, however, less subject to alterations of oxygen consumption rate by temperature changes throughout the rest of the year. Thermal insensitivity (the presence of a thermoneutral zone) throughout a portion of the temperature range has also been reported for the oxygen consumption rate of Littorina irrorata (Shirley et al., 1978). Bayne & Scullard (1978) recommended that a statistical discrimination be made for experimentally derived b values in the equation log PO, = log a + b log W. The common regression exponent, b, was found to be 0.60 f 0.07 (SD) in our experiments. This value is not statistically different from the b value of 0.51 that was derived for Thais lapillus by Bayne & Scullard (1978). Stickle (1973) found b values ranged from 0.2 to 1.0 with a mean value of 0.60 in T. lamellosa. The f0, values obtained in our study compare closely with those obtained by other authors. The PO? for a 250-mg snail ranged from 10 ~10, . h-’ at 5 “C and 17.5 y&,S to 60 ~1 0, . h -’ at 20 “C and 20 %,, S. Bayne & Scullard (1978) reported a winter (9-14 “C) QO, of 61 and a summer (15-20 “C) value of 88 ~1 0, . h-’ for a 250-mg dogwhelk from the same population. Sandison (1966) reported a mean PO, of 55 ~1 0, . h-’ for a 250-mg dogwhelk at 18 “C. Ammonia excretion rates were less affected by temperature than t0, as judged by Q,, values. In addition, pNH,+ did not vary as a function of salinity at 5 “C nor did it vary systematically with salinity at 10, 15 or 20 “C. This tinding is probably due to the protein-oriented catabolism of T. lupillus. PNH: varies as a function of salinity in stepwise-acclimated T. lapillus in a different pattern from that observed in T. lamellosa or T. emarginatu. Stickle (1970) found the ammonia excretion rate of T. lamellosa to be significantly lower at 15 X S than at 20, 30 or 40 %, S. Emerson (1969) found the ammonia excretion rate of T. lamellosa to be significantly higher in 100% sea water (= 35 y&,s) than in 50 or 150% sea water after 1 wk at each salinity. He found, however, no significant difference in the ammonia excretion rate in T. emarginata in 100 and 50% sea water after 1 wk in each salinity. Net flux rates of primary amines across the body surface of T. lapillus indicate a loss of primary amines from the snail. Assays were carried out at ambient-water
14
primary
W. B. STIC‘KLL
amine
concentrations
AI\;D
of 0.6-5.5
B 1. BAL Nk
PM. This primary-amine
loss from
the
dogwhelk accounts for a significant percentage of excreted nitrogen. Primary-amine loss varied from 7 to 41”/, of ammonia excretion in T. lupillus. Relatively more amino-N was excreted at 17.5”/, S than at all other salinities. Bayne & Scullard (1977) have shown seasonal and habitat differences in the relative amounts of primary amine and ammonia excreted by three species of Mytilus. Conover & Corner (1968) gave a theoretical minimum value of 8 for the 0 : N ratio if only protein is catabolized, but Mayzaud (1973) calculated 0 : N ratios of 4.4 for mammalian proteins and 2.3 for Calanus jinmarchicus proteins. Thuis lupillus predominately catabolizes protein as shown by 0: N ratios which varied between 4.2 and 13.1, when nitrogen excreted was the sum of ammonia and primary amines; 5.9 and 15.6 when ammonia is considered the only nitrogen species excreted. Stickle (1975) estimated that a female T. Iamellosa received 94’1/,, of its energy from protein catabolism during aggregation for reproduction, and 6% from carbohydrate catabolism. Temperature and temperatureesalinity interaction affected 0 : N ratios in our study; the 0 : N ratios were significantly higher at 15 “C than at 5, 10, and 20 “C and significantly lower at 5 “C than at 10, 15, or 20 “C. Oxygen: nitrogen ratios appear to be higher in herbivores than in carnivores. probably reflecting the nitrogen-rich diet of carnivores. For example. Conover & Corner (1968) divided the copepods they studied into a herbivore group consisting of Calanus and near relatives and an omnivore-carnivore group consisting of the Mctridiu-Parenchaeta group. Carnivores had higher respiration and excretion rates than herbivores, with lower 0: N ratios that cycled less seasonally. The herbivore Mytifus edulis in unstressed conditions frequently exhibits 0 : N ratios >40. The 0 : N ratio of the herbivorous sea urchin Strongylocentrotus drohachiensis (0. F. Miiller) at 30 &, S and 13 “C is 38 (unpubl.). Capuzzo & Lancaster (1979) found the 0 : N ratio of Homurus americanus larvae fed on brine shrimp to indicate principally protein catabolism (x 28) and to decline to = 23 during the last two larval
stages
indicating
even
more
reliance
on protein
as a metabolic
substrate.
Unpublished data from our laboratory have shown the 0 : N ratio of Thai.7 haemastoma (Linne) at 30°C and 30”/, .S to be 7.7 and that of T. lima (Cimelin) at 30ym S and IO’< to be 16.0. Information gathered to date indicates that unstressed herbivores have high 0 : N ratios ( > JO), whereas carnivores exhibit low 0 : N ratios. Long-term starvation (89 days) had ;I significant effect on oxygen consumption and nitrogen excretion of T. lapifhrs. Although the rate of oxygen consumption by snails declined by 2X”,, during the 89 days without food, this decline was more than accounted for by a 37”,, decline in tissue weight. No change occurred in the recalculated intercept (J and the weight-specific respiration rate incrctlscd by 17”,, (Table VI). Bayne & Scullard (1978) noted the oxygen consumption rate of 7‘. lupiilzrs declined during 18 days starvation and also found a decline in the intercept value. a. with starvation. Different patterns in the change of ox!‘-en consumption
RESPIRATION
AND NITROGEN
EXCRETION BY THAIS
15
rate with starvation in the two studies may have been due to two causes. First, whereas all snails in the study of Bayne & Scullard (1978) had just fed when the starvation studies began, giving a uniformly high rate of oxygen consumption, snails used in the present study were at all stages of the feeding cycle at the beginning of the starvation experiment. This difference in methodology would have the effect of lowering the control respiration rate in our study. Secondly, Bayne & Scullard (1978) did not note any change in the locomotory activity pattern of T. lapillus during the 18 days’ starvation. We observed increased crawling by the snails in the Gilson vessels during our longer-term starvation study. Calow (1972) has also noted increased crawling in some snails during starvation. Stickle & Duerr (1970) and Stickle (1971) found constant or increased rates of weight-specific oxygen consumption by T, lamellosa during 53 and 91 days starvation. Ammonia excretion by T. lapillus increased throughout the starvation period of the dogwhelk, whereas the primary-amine loss rate increased to Day 21 and declined to control levels by Day 89. Consequently, the 0: N ratio indicated that the catabolism of protein for energy during starvation met almost all of the snails energy needs. This finding is not surprising, for protein constitutes the majority of the body in muricids such as T. haemastoma (Belisle & Stickle, 1978) and T. lamellosa (Stickle, 1975). ACKNOWLEDGEMENTS
W. Stickle gratefully acknowledges Louisiana State University for granting him a sabbatical leave which allowed him to do this work. Special thanks go to Mr. R. Glover, Director of the Institutk for Marine Environmental Research (IMER), for providing the opportunity to work at IMER. It was indeed a pleasure to interact with all involved in the experimental ecology programme. Special thanks go to Dr. J. Widdows, and to Miss M. Day for performing some of the oxygen consumption and nitrogen excretion experiments.
REFERENCES BAYNE,B. L., 1975. Aspects of physiological condition in Mytilus edulis L., with special reference to the effects of oxygen tension and salinity. In, Proc. 9th Eur. Mar. Biol. Symp., edited by H. Barnes, Aberdeen University Press, Aberdeen, pp. 213-238. BAYNE, B.L. & C. STULLARD,1977. Rates of nitrogen excretion by species of Myrilus (Bivalvia: Mollusca). J. Mar. Biol. Assoc. U.K., Vol. 57, pp. 355-369. BAYNE,B. L. & C. SCULLARD,1978. Rates of oxygen consumption by Thais (Nucella) lapillus (L.). J. Exp. Mar. Biol. Ecol., Vol. 32, pp. 97-I 11. BELISLE,B. W. & W. B. STICKLE,1978. Seasonal patterns in the biochemical constituents and body component indexes of the muricid gastropod, Thais haemastoma. Biol. Bull. (Woods Hole, Mass.), Vol. 155, pp. 259-272. BOYDEN,C. R., J. H. CROTHERS,C. LITTLE & C. METTAM,1977. The intertidal invertebrate fauna of the Severn Estuary. Field Stud., Vol. 4, pp. 477-554.
16
W. B. STICKLE
AND
B. 1.. BAYNt
C’,\LUW. P., 1972. The structural and functional dynamics of selected species populations of freshwater snails: towards a systems approach. Ph.D. thesis, University of Leeds. 468 pp. fa~r;zzo. J. M. & B.A. LANCASTER, 1979. Larval development in the American lobster: changes in metabolic activity and the 0: N ratio. Cart. J. ZooI.. Vol. 57. pp. 1845-1848. CARRIKER, M.R., 1955. Critical review of the biology and control of oyster drills Urosalpinx and Eupleura. Spec. Sri. Rep. U.S. Fish Wildl. Serv. Fish No. 148, 150 pp. CONNELL, J. H., 1961. Effects of competition, predation by Thais kupidlus,and other factors on natural populations of the barnacle Balunus balanoides. Ecol. Monogr., Vol. 31. pp. 61-104. COTWELL, J. H., 1970. A predator-prey system in the marine intertidal region. I. Bolun~~ glandulufaand seven predatory species of Tbais. Ecof. Monogr., Vol. 40. pp. 49.78. foNNEl.L, J, H., 1972. Community interaction on marine rocky intertidal shores. At~trrc. Rcr. &of. S~sr.. Vol. 3. pp. 169-192. CONOVER, R. J. & E. D. S. CORNER. 1968. Respirdlionand nitrogen excretion by some marine zooplankton in relation to their life cycles. J. Mar. Biol. A.v.roc. U.K., Vol. 48, pp. 49. 75. EMERSON, D.N., 1969. Influence of salinity on ammonia excretion rates and tissue constituents 01 euryhaline invertebrates. Camp. Biochem. Physiol., Vol. 29, pp. 1115-l 133. FIKDLEY. A. M., B. W. BELISLE & W. B. STICKLF.. 1978. Effects of tidal ~ucf~iari~~ns 01‘ salinity on ~hc respiration rate of the southern oyster drill. Tbais huema.siomu. and the blue crab, C~~i~~~~c~~,.~ ~~~idl~s. Mar. &of.. Vol. 49, pp. 59-67. FINNPY, D. J., 1971. Probif analysis, Cambridge University Press. C’ambridge. 3rd edition. 230 pp. FIX HER, E.. 1928. Recherches de bionomic et d’oceanographic littorales sur La Rance et ie littoral de la Manche. Ann. Inst. 0cc;anogr. (Monaco), Vol. 5, pp. 201429. C&WON, D. & W. B. S~rrlc~e. 1980. Effects of salinity and temperature on the predation rate of Tbai.r baemo~ioma on Crassostrea virginicu spat. Biol. Bull. ( Wuodr Hole. Mass.). Vol. 158, pp. 4957. C&\~,~NI.OCFI. J. N.. 1927. Contributions to the study of marine gastropods. II. The intertidal life ol Bwcinum undatum, a study of non-adaptation. Cotrrr. Can. B&l. F&/t.. N.S.. Vol. 3. pp. 167177. GR~ss~oF~‘. K. & H. JOI+ANNSE~~. 1972. A new sensitive and direct method for the automatic determination of ammonia in seawater. J. Corrs. Perer. hrf. Esplur. Mrr. Vol. ?4, pp. S16 571, M\\T,~~‘D. P.. 1973. Respiration and nitrogen excretion of zooplankton. II. Studies of the metabolic characteristics of starved animals. Mar. Biol.. Vol. 2 I _pp. 19 -28. MEN~;E, B.A.. 1976. Organization of the New England rocky intertidal community. Role of predation, competition, and environmental heterogeneity. Ecol. Monogr., Vol. 46, pp. 355-393. MEN(;E, B.A. & J. P. SUTHERLAND, 1976. Species diversity gradients: synthesis of the roles 01‘predation, competition, and temporal heterogeneity. Ant. Nat.. Vol. 1 IO. pp. X1-369. NORTH, B. B., 1975. Primary amincs in California coastal waters: utilization by phytoplankton. Lirrr&. Oceonogr., Vol. 20, pp. 20-27. OKI-ANI), F.. 1933. Litoralstudien an der Skagerrakkuste Norwegens: die Vcrbcnung van Pm-pure lopiilus, Pate/la vuigaia an den Littorina-arten in Fromo. Zoogcqqapbica, Vol. I pp~ 579601. P~Iw, R. T.. 1966. Food web complexity and species diversity. Anr. Nat., Vol. I(@, pp. 65-75. Si-. AM&%? , L. S., 1938. Studies on the biology of the L,ouisiana oyster drill.7%ak ~~or;~/f~~?o bqwt Clench. M.S. thesis. Louisiana State University. Baton Rouge, I16 pp. SI AMANT, L.S.. 1957. The southern oyster drill. La Wi’/d/. F’irh. Comnr.. Sc~unth txant~~~alRept. 19S6 57, pp. 81-85. SAl\i>lSON. E. FL. 1966. The oxygen consumption of some litloral gastropod,\ m relation IL, zonation. J. 2001. flondoB/. Vol. 149. pp. 3633173. Sttrnt tv. T.C.. G. J. DENOUX & W. B. S~IIXLI-. 1978. A seasonal investigati[~n of respiration of the marsh periwinkle, Litrorimr iwtrora. Biol. &if. ( Woo& Hole. .Masr.). Vol. 154, pp. 322.-334. S~I.<)R~~NO. L.. 1969. Determination of ammonia in natural waters by the pheoofhypochlorite method. L~tnnol. Oceanogr.. Vol. 14, pp. 799-801. SI I(XI I:. W. B., 1970. Some physiological aspects of the reproductive cycle of the intertidal prosobranch Tlrrric kumellosa (Gmelin. 1972). Ph.D. thesis, University of Saskatchewan, Regina campus. 160 pp. ST I(‘XLI:. W. B.. 1971. The metabolic effects of starving Thuis /ame&~.sa immediately after spawning. (bmp. Biocbem. Phwioi.. Vol. #A. pp. 627-634. %trci(t1) W. B., 1973. The reproductive physiology of the intertidal prosobranch 77z~llri.s ~~~/~~~~~).s~~ (Gmelin). J. Seasonal changes in the rate of oxygen consumption and body component jndexes. Viol. Bull. ( Woo’o0d.c Hok, Mass.). Vol. 144. pp. 51 l--524.
RESPIRATION
AND NITROGEN
EXCRETION BY THAIS
17
W.B., 1975. The reproductive physiology of the intertidal prosobranch Thnb lamellosa (Gmelin). II. Seasonal changes in biochemical composition. Biol. Bull. (Woods Hole, Mass.), Vol. 148, pp. 448460. STICKLE, W. B. & F.G. DUERR, 1970. The effects of starvation on the respiration and major nutrient stores of Thais lamellosa. Comp. Biochem. Physiol., Vol. 33, pp. 689-695.
STICKLE,
Elsevier Biomedical Press
EFFECTS OXYGEN
OF TEMPERATURE
CONSUMPTION
AND SALINITY
AND NITROGEN
THAIS (NUCELLA) LAPILLUS
ON
EXCRETION
IN
(L.)
W. B. STICKLE’ and B. L. BAYNE Institute for Marine Environmental
Research, Prospect
‘Place. The Hoe, Plymouth
PLI 3DH, U.K.
Abstract: The 2-wk TLm of stepwise-acclimated Thais lapillus (L.) ( >20 mm long) was 14.2-16.2% salinity (S) at 5, 10, 15, and 20 “C. The same TLm occurred at 10 “C after direct transfer of snails to the final salinity but stepwise-acclimated small snails ( ~20 mm) tolerated a significantly lower salinity (12.7% S). Oxygen consumption rates (PO,) tit the allometric equation fi0, = a. W”.60*‘.O’. Salinity and temperature had a significant effect on @O,, which was highest at 30% S and depressed at 17.5% S and at 5 “C. Ammonia excretion rates fit the allometric equation tNH$ = a . W”.6’* ‘.05. Both salinity and temperature affected VNH$. Ammonia excretion was significantly lower at 17.5 % S than at higher salinities at 10, 15, and 20°C but did not vary as a function of salinity at 5°C. Primary amines were lost from snails under all conditions without any obvious relationship with temperature or salinity. Primary-amine loss, expressed as a percentage of PNH;, was significantly higher at 17.5 56, S than at higher salinities. Oxygen : nitrogen ratios ranged from 4.2-15.6, indicating protein was the primary metabolic substrate, and were highest at 15 “C and lowest at 5 “C. Snails withstood 89 days starvation without mortality at 10°C. Oxygen consumption of snails declined by 28% during starvation due to a 37% decline in dry weight; consequently, weight-specific respiration rate increased by 17%. The intercept (a) for the fi0, allometric equations did not change during starvation. Ammonia excretion increased during starvation, and primary-amine loss increased until Day 21, then declined. Oxygen : nitrogen ratios declined from 14 to 8, indicating an increased catabolism of protein during starvation.
Water temperature and salinity vary tidally and seasonally within estuaries. Synergistic interactions between these variables can be expected to regulate the distribution and activity of many estuarine invertebrates. Muricid gastropods are important predators of mussels, oysters, and barnacles in the food webs of marine hard substrata (Carriker, 1955; Connell, 1961, 1970, 1972; Menge, 1976; Menge & Sutherland, 1976; Paine, 1966). Many species of muricid gastropods do not, however, survive in low salinity regions of estuaries. For example, the low-salinity limit of Thais lapillus in the Severn Estuary is 20-28 &, S (Boyden et al., 1977) while that of T. haemastoma is z 15 “/, S (St. Amant, 1938, 1957). T. haemastoma will, however, tolerate 7.5% S at 10, 20, and 30°C for at least a month following laboratory acclimation (Garton & Stickle, 1980). ’ Permanent address: Zoology and Physiology Department, LA 70803, U.S.A.
Louisiana State University, Baton Rouge,
0022-0981/82/OOOO-OOOO/$O2.75 0 1982 Elsevier Biomedical Press
2
W. B. STICKLE
AND
B. L. BAYNE
The rate of oxygen consumption of acclimated muricid gdstropods varies with temperature, salinity, and time since their last meal. Little acclimation of oxygen consumption occurs with seasonal changes in water tempe~ture in T. lap~~il4.~ (Bayne & Scullard, 1978) or T. lamdlosrc: (Stickle, 1973). The rate of oxygen consumption of T. lamehsa is significantly lower at 15 x0 S than at 20, 30, or 407$, S (Stickle, 1970) whereas the rate of oxygen consumption of T. Izcrrmastoma is significantly lower at 10 yWS than at 20 or 30% S (Findley PI al., 1978). Bayne & Sculiard (1978) found the rate of oxygen consumption of T. /~~~j~l~,s to be high during feeding but to decline during 18 days of starvation. in contrast. the rate of oxygen consumption by T. lamellosa remained constant or increased during 53 days (Stickle & Duerr, 1970) and 91 days starvation (Stickle, 1971). The metabolic substrata catabolized by T. Iumellosu during starvation varied with the stage of the reproductive cycle, but protein was always the major nutrient utilized (Stickle & Duerr, 1970; Stickle. 1971). Ammonia excretion is also modified by temperature, salinity. and starvation in T. lamellosa but no data exist for T. lapillw. Stickle (1970) found the NH,* excretion rate of T. lamellosa to be higher at 9 than at 15 “C. Snails used for the 9 “C experiment had, however, starved for over 2 months while in reproductive aggregations before the NH; excretion rates were determined. Stickle (1970) also found that the NH: excretion rate of T. Iameihsa acclimated to 15 %, S was significantly lower than that of snails acclimated to 20, 30, or 40’&, S. The net flux of primary amines (free amino acids) has not been determined for any species of gastropod at environmentally realistic ambient concentrations of amino acids. Several methods exist for the estimation of the relative amounts of carbohydrate, lipid, and protein catabolized by animals. The calculation of the respiratory quotient (RQ) is notoriously unreliable in animals which possess calcareous skeletons because carbon dioxide, produced via respiration, may be fixed in the calcareous shell material. Conover & Corner (1968) first used the ratio of oxygen consumed to nitrogen excreted in atomic equivalents (0 : N ratio) as an indication of biochemical substrate metabotized. A high 0: N ratio is indicative of carbohydrate and/or lipid catdbo1ism while a ratio as low as 4-8 indicates that only protein is being catabolized (Conover & Corner, 1968; Mayzaud, 1973). The present study was undertaken to determine the en‘ects of temperature, salinity, and starvation on the survival, rate of oxygen consumption, ammonia and primary-amine excretion, and 0: N ratios of the muricid gastropod, T. la~ii~~ (L.). Two other studies will report on the effects of temperature and salinity on the Scope for Growth, growth efficiencies, feeding cycle, lysosomai fragility, and correlation of stress indices in 7: lapillus.
RESPIRATION AND NITROGEN EXCRETION BY THAI.5 MATERIAL
AND METHODS
T. ~~~~1~~s were collected at low tide from a rocky shore at Bovisand, South Devon, England. Collections were made during September, 1978, and during January and February, 1979, at an ambient salinity of 34.5 x0. Water temperature was within 3 “C of the respective experimental temperatures of 5, 10, 15, and 20°C. Snails were stepwise-acclimated to test salinities of 10, 12.5, 15, 17.5, 20, 25, 30, and 350/, at a rate of 2 y&,S per day. The 35 y&,S treatments were inadvertently omitted at 15 and 20 “C. Snails were provided mussels (Mytifus eMis L.) for prey, except during the fasting experiment and during the time it took to determine rates of oxygen consumption and nitrogen excretion. SURVIVAL EXPERIMENTS Survival of Thais lapillus ( >20 mm long) was determined on groups of 25-40 snails per salinity after 2-wk exposure to the test salinities. Survival was also determined after 5-wk exposure to the test salinities at 5 “C because of the longer time it took snails to die. In addition, snails ( r20 mm long) were directly transferred to all test salinities at 10 *C to compare results with those for stepwise-acclimated snails. Finally, survival of juvenile snails ( < 20 mm long) was determined at 10 “C after stepwise acclimation. EXPERIMENTAL DESIGN Three series of experiments were carried out to determine the effects of tempersalinity, and starvation on physiological rates in T. lupillus. (1) After determining survival, we measured the feeding rate of 30 snails, representative of the size range characteristic of the Bovisand population, for 3 wk at 17.5 and 30 “/, Sand at 5, 10, 15, and 20 “C. The oxygen consumption and nitrogen excretion rates were then determined for each experimental group of snails which will be identified as the “predator-prey” series. (2) In a second set of experiments, 10 snails of standard length (23-28 mm) were used in feeding rate experiments at 17.5, 20, 25, and 30”/, S and at 5, 10, 15, and 20 “C for 3 wk. Feeding rates were also determined for standard length snails at 35% S and 5 and 10°C. Oxygen consumption and nitrogen excretion rates were determined for each group of snails before and after the 3-wk feeding rate experiment. (3) Finally, the rates of oxygen consumption and nitrogen excretion were determined for 12 snails on 0, 21, 49, and 89 days of fasting at 10 “C and 30 y&,S. Estimated dry weight before the feeding rate experiments and during the fasting experiment was obtained for each snail by prediction of the initial weight from total length. Separate dry weight to length regression lines were constructed for each sex from a group of snails collected at the same time as the experimental snails. Females were significantly heavier per unit length than males. Predicted
ature,
W. B. STICKLE
-I
AND B. L. BAYNE
weight at any time was obtained
by correcting
the appropriate decimal end of the experiment.
fraction
of dry weight change
OXYGEN
EXPERIMENTS
The
CONSUMPTION
rate
of oxygen
consumption
the predicted
of snails
was
initial
between
determined
dry weight by
collection
with
and the
a Gilson
Differential Respirometer equipped with 1 IO-ml reaction flasks. 40 ml of Milliporetiltered and air-saturated sea water of the appropriate salinity was added to each reaction flask, and flasks were shaken at the slowest rate. Snails crawled about and remained submerged throughout all experiments. Oxygen consumption rates were corrected to N.T.P. as ~1 0, .h -‘. AMMONIA
AND PRIMARY-AMINE
EXCRETION
EXPERIMENTS
Snails were placed into 100 ml Millipore-filtered and air-saturated sea water of the appropriate salinity for 4 h. Control beakers containing sea water from the same batch, but with no animals, were incubated for the same time. Excretion rates were determined as the difference between the ammonia and primary-amine content in the beakers containing snails and the control beakers. Plastic restrainers kept snails below the surface of the water. Ammonia levels were determined by a modification (Grasshoff & Johannsen, 1972) of the method of Sol6rzano (1969) with ammonium sulphate used as the standard. Primary-amine (free amino acid) levels were determined by the fluorescamine method of North (1975) using leucine as a standard. OXYGEN
: NITROGEN
RATIOS
The 0: N ratio was determined in two ways after conversion of the oxygen consumption. ammonia and primary-amine excretion rates to atomic equivalents. 0 : N ratios were calculated on the basis of ammonia the basis of the sum of ammonia and primary-amine STATISTICAL
excretion excretion
rates alone and on rates.
ANALYSIS
Survival data were analysed by the method of Finney (1971) and presented as the TLm + the 95% fiducial limits. Significant differences between individual TLm values are given as regions of non-overlap of the 95J?,; fiducial limits. In the initial data analysis of oxygen consumption, ammonia and primary-amine excretion, the relationship between physiological rates and body weight were described for each predator-prey experimental condition by the allometric equation : Y = uX”, where Y = the physiological rate, X = the dry flesh weight (in mg) and h and log,,,a are the slope and intercept of the log,,, Y/log,,,X regression, respectively. The individual regression lines for each rate function were then compared by analysis of covariance
RESPIRATION
AND NITROGEN EXCRETION
BY THAZS
5
to test whether the slopes were significantly different. Because signi~~nt differences in slopes, a common regression coefficient that was then used to re-calculate the intercepts of all three sets Analysis of variance was used to test variation among treatments Multiple Range Test was used to identify significant differences treatments.
there were no was -eakulated of experiments. and Duncan’s between those
RESULTS SURVIVAL AS A FUNCTION
OF TEMPERATURE
AND SALINITY
T. i~p~l~u~( >20 mm long) tolerated a slightly lower salinity at 5 (5 wk), 10, and 20 “C than at 15 “C (Fig. 1). The 2-wk TLm was si~i~~antly lower than the
TLm
30
IO
5
TEMPERATURE
I5
20
(“Cl
Fig. 1. Survival of large ( >20 mm long) This fap~~Zusas a function of temperature and salinity is given as median tolerance limits (TLm) f the 95% confidence interval: unmarked data, 2-wk TLm of stepwise acclimated snails; n , 5-wk TLm at 5°C; DT, 2-wk TLm of snails directly transferred from 34.5ym S to the test salinity; J, 2-wk TLm of juvenile snails which were ~20 mm long.
5-wk TLm at 5 “C. There was no signi~cant difference in the TLm for large ( >20 mm long) T. ~up~~~us stepwise acclimated or directly transferred to experimental salinities at 10 “C. Small snails ( ~20 mm) tolerated lower salinity (12.7%) than large snails ( >20 mm; 15.1 X s) at 10 “C. OXYGEN CONSUMPTION
EXPERIMENTS
Oxygen consumption data from the predator-prey experiments were subjected to analysis of covariance to test for statistical differences in slopes and intercepts
W. H. STIC‘KLF.
h
AND
13.L. BAYNtr.
when oxygen consumption (~1 0: h ’ = PO?) was regressed on dry flesh wt in mg ‘fW) after logarithmic transformation. Differences between slopes were not significant (P < 0.05). The regression exponent (h) was 0.60 + 0.07.
Antifogs
of the intercept values (u) + st and Q,,, t’or o.~ygccnconsumption
feedine-rate experiments
ol‘ Uwj
IqiNw
used in the
of ~2 usin p a common value kitr h = 0.60 in the equation: log,,, @‘(I2 = log,+z + 0.60 loglo I+‘. where pa, is given in 1.11 0, h ’ and Ci’ IS given in mg dry flesh wt
OlOvaluesare given
after re-calculation
for the temperature
intervals 5 10 f’. ------._-__ Temperature
5
I0
I5
If) IS ‘C. and I5 31°C‘: N.D.. ...____-_
:
no data.
(‘C)
10
“_-_...__. 5 IO
IO I
f5 -70
Salinity inrercepts ‘i
CX)
-
Yltl
17.5 10
0.37 * 0. I.5 0.58 f 0. IS
0.7.: & 0.16 0.96 + 0. lb
f.O2z1:0.15 0.K rt 0. I7
0 78 * 0.14 l.l2~0.5
: ‘J 2.-
2.0 (I 7
‘5 30 i’;
0.49 + 0.15
1.01 + 0.16
I.10 $I 0.17
1.04+(r.lh
1.2
I .06f 0.17 lb
l.lO&.
l.f6+0.17
21
I2 I I
0.51+ 0.14 0.48 i 0. f 5
0.90 + 0.
0.17
KD N.D. -_.--.-~~_-.-.~__.~
3s -.____...
&.I>. __-
0.6
I .9 0.9 I.1 N.D.
Intercept values (u) of log PO, regressed on log dry wt for the feeding experiment snails were re-calculated with a common slope of 0.60. Q,,, values were calculated from these data (Table I). Quantitative agreement between the predator-prey and feeding-rate data sets for the same treatment was very good. 1:‘02 intercept values were highest at 15 and 20 “C and 30x, S while snails exhibited lowest intercept values for PO, at 5 “C (Duncan’s Multiple Range Test). High Q,,, values between 5 and 10°C coupled with low intercept values indicate suppression of oxygen consumption at 5 “C. The oxygen consumption rate of dog-whelks was well acclimated to temperature between 10 and 20 “C. To test for the effects of temperature, salinity, and time on snail @OZ. the data sets were analysed by first calculating, for each measurement in each data set, PO, . W -’ 6oand then calculating the mean value of each set, The mean 60, . W m” represents the rate of oxygen consumption per unit of metabolic body size, thus excluding variance between sets that is due to differences in body weight. Mean PO, . W -‘M values were then analysed in a three-way anatysis of variance with the variables being temperature, salinity, and time (before and after the 3-wk feeding experiment). Temperature (P < 0.001) and salinity (P < 0.001) had a significant effect on GO2 W -““, but there was no effect due to time. Therefore, the initial and final PO, . W -““’ for each data set were averaged to give mean oxygen consumption per unit of metabolic body size for each saIinjty--tem~erat~e combination. Duncan’s Multiple Range Test indicated that the salinity effect on cO1_. W -“bo is due to a depression of oxygen consumption at 17.5 “/w S at 5, IO,
RESPIRATION
AND
and 20 “C and the temperature all salinities (Fig. 2).
2.5
P b
NITROGEN
7
BY THAIS
EXCRETION
effect is due to depressed PO, . W -“.60 at 5 “C and
5ec
P!OW
50
2.0 2 6 ‘3 -ei
\ 1.5
9
+M-+-+
0.5
i
i
+
500
20 5 d
I++-+-+\
1.0
+’
15
‘3
. IO 4-9 I 5m II
L
15
20
25
30
35
b
I5
20
L
I
I
I
I
25
30
35
I5
20
1
1
25
30
J
’
’
’
I5
20
25
30
SALINITY (%d Fig. 2. Average oxygen consumption and ammonia excretion data for Thais lapiNus are presented as to,. W-o.6oand pNH$ W-o.6’ which represent the rates per unit of metabolic size and exclude variance between data sets due to differences in body weight: data are presented as the mean f I SE.
AMMONIA
EXCRETION
EXPERIMENTS
Predator-prey data sets of ammonia excretion rate were used to test for the interaction between temperature, salinity, and body size. Ammonia excretion rate, PM NH: . h-’ = PNH:, was regressed on dry flesh wt, in mg ( W), after logarithmic transformation, for each temperature-salinity combination and then subjected to analysis of covariance. Differences between slopes were not significant (P >0.05) but differences between intercepts were (P < 0.001). The pooled exponent was 0.61 & 0.05 so the regression equation becomes pNH,+ = a . W”.61*‘.O’. Intercept values (a) were re-calculated with a common slope of 0.61. Agreement between the predator-prey groups and average rate from the initial and final data sets from the feeding-rate experiments was good but not as close as occurred with the PO, data. Re-calculated intercept and Q,, values from the feeding rate experiments are given in Table II. Re-calculated intercept values of pNH,+ do not vary as a function of salinity at 5 “C but are significantly lower at 17.5 X than at higher
8
W. B. STICKLE AND B. L. BAYNE
salinities at 10, 15, and 20 “C according to Duncan’s Multiple Range Test. Values for Qt, were low between each temperature tested in this study.
Antilogs of the intercept values (u) &SE and Q,,, for NH; excretion of 7‘hcti.s lupdlus used in the feeding-rate experiments after re-calculation of a using the common value for h = 0.61 in the equation: W..13given in mg dry i0gloti~ri4+ = 10g,,a + 0.61 logluWwhere ~‘NH,+ isgiveninnMNH$.h-‘and flesh wt; Qlo values are given for the temperature intervals S- 10°C. IO- IS’<‘. and 15%20°C; N.D., no data. ‘Temperature (“C)
Salinity (%o)
17.5 20 25 30 35
5 _~~~~~~_~._ ._.
I0
15
20
5 IO -.
Intercepts li
..__“._,___~~~_~~~~__._. _... ..~ ~_~_....--.._ 1.88 f 0.1 I 1.84*0.12
I .Y3f 0.I I I .93 + 0.11 1.89 + 0.11
1.88* 0.12 2.27 +_0.12 2.34 + 0.12 2.27 f 0. I3 2.22 + 0.12
2.14~O.lI 2.24 + 0.13 2.39f0.13 2.25 rf:0.13 N.D.
2.24 f 0.11 2.36 + 0.11 2.37 t 0.13 2.44Ito.13 N.D.
IU- IS
1%20
._..
911, ~~ _ ~~ ._.. ..__ ._.__ I 00 1.23 t.47 1.58 1.3s
1.30 0.99 I .04 O.98 N.D.
1.10
1.05 0.98 I.18 N.D.
To test for the effects of temperature, salinity, and time on @‘NH:, the rate of ammonia excretion per unit metabolic size (PNH; . W-““I) was calculated for each observation. The average value in each data set was calculated to exclude variance between data sets due to differences in body weight. Mean 6’NH: +Wy-Ohl rates were then analysed in a three-way analysis of variance as was done with GO,. Temperature (P < 0.001) and salinity (P (0.01) had a significant effect on ~NH; . W -‘A’ but there was no effect due to time (P >0.05). Taking the average of the initial and final PNH; W -“A’ values for each data set, overall average rates per unit metabolic size show the salinity effect to be due to an enhancement of ammonia excretion at 25 & S and 15 “C as well as depressed ammonia excretion at 1’7.50/, S and 10°C (Fig. 2). There is no detectable salinity effect at the temperature extremes of 5 and 20°C. The temperature effect is due to a large increase in FNH: between 5 and 10 “C (Duncan’s Multiple Range Test). PRIMARY-AMINE
EXCRETION EXPERIMENTS
Predator-prey data sets of primary-amine excretion rates by 7: lapillus were used to test for differences due to temperature, saiinity, and snail dry weight. In the pooled regression of amine excretion and body size, the F value (1,152 d.f.) is only 5.8 1 and the correlation coefficient is 0.19. The biological relevance of the regression is, therefore, marginal. Therefore, all the data from the feeding rate experiments were pooled and presented as nM primary amines excreted per g dry-flesh wt and as a percentage of the PNH: excretion for the same snails (Table III).
RESPIRATION
AND NITROGEN
9
EXCRETION BY THAIS
No significant differences existed between the initial and the final rates of primary-amine loss from snails, so average values are presented for all treatments (Table III). ~i~i~~nt variation existed in the average rates of primary-amine excretion (P <0.0.5), but this was due largely to temperature-salinity interactions. III
TABLE
Average primary-amine loss rate in nM . g -’ ’ h-I and expressed as a percentage (in parentheses) of NH: excretion rate for Thnis~apjllus during the 3-wk feeding cycte experiment. Temperature (“C) Salinity (L) 17.5 20 2s 30
S 316 104 109 363
(41) (13) (18) (30)
10 121 236 144 61
(25) (16) (11) (7)
15 221 173 326 111
(19) (20) (33) (20)
20 321 226 246 124
(30) (23) (13) (17)
Duncan’s Multiple Range Test indicated that the excretion rate at 5 “C and 30 %,,S was si~i~cantly higher than at all other treatments, whereas the loss rate at 10°C and 300/, S was significantly lower than at ail other salinities. When primary-amine loss rates were expressed as a percentage of 9NH,’ from the same snails, only 3 of 18 paired t-test comparisons showed a significant difference between the initial and final data sets for each treatment. Therefore, average values were calculated for each treatment. Salinity exerted a significant effect on this relationship (P < 0.05) but temperature did not. Duncan’s Multiple Range Test showed primary-amine excretion rates to comprise a higher percentage of ammonia excretion at 17.5 y&,S than at all other salinities. OXYGEN : NITROGEN RATIOS
Predator-prey data sets of the 0 : N ratios were analysed for temperature, salinity, and interaction effects with dry weight. No significant treatment or treatment-dry weight interaction occurred in the analysis of covariance for data sets that utilized only ammonia as nitrogenous excreta or those that summed ammonia and primaryamine excretion rates. Therefore, data from the feeding rate experiments were analysed for differences in 0: N ratio between the initial and final determination of oxygen consumption and nitrogen excretion. No significant differences existed between the paired data sets for each treatment, so the initial and final 0 : N ratios were averaged for each snail before mean 0 : N ratios were determined for each treatment (Table IV). With regard to data sets using ammonia as the only nitrogen excreta, significant variation existed between treatments (P < 0.0001) which was due to a temperature effect (P < 0.0001) and temperature-salinity interaction (P < 0.005). Duncan’s
W. B. STIC‘KLt
RhD
8. L.. HAYNE
RESPIRATION
AND NITROGEN
EXCRETION
BY THAIS
11
Multiple Range Test shows the 0 : N ratios to be significantly higher at 15, than at 10 and 20 “C, whereas those at 5 “C are significantly lower; identical statistical results occurred when ammonia and primary-amine excreta were combined, but the 0 : N ratio for a given treatment was then l-2 units lower. FASTING
STUDY
Oxygen consumption and nitrogen excretion rates were dete~ined on Days 0, 21,49, and 89 of fasting (Table V). The oxygen consumption rate declined by 28% when expressed on a per snail basis but increased by 17% when expressed on a g dry-tissue wt basis during the 89-day fasting period. Tissue weight had declined by 37% during the fasting period. Ammonia excretion rate increased by 15% when expressed on a per-snail basis and by 81% when expressed on a dry-tissue wt basis. Primary-amine excretion increased from the control level to maximum values on Day 21 and then returned to the control level by Day 891when expressed on both a per-snail and a per dry-wt basis. The 0 : N ratio indicated that T. lupillus primarily catabolized protein during fasting and its reliance on protein increased with the fasting period up to 49 days and did not change by Day 89.
DISCUSSION
T. iapilhs tolerated lower salinity in our study (14.2-16.2 % S) than the 22.8 “/ S minimum reported by Fischer (1928) or 20-25 “I, S found in the summer by Okland (1933). Temperatures between 5 and 20°C did not influence the salinity tolerance of the dogwhelk, whose geographical range is from the 0°C winter isotherm, in the proximity of the northern limit of its distribution, to 35-35.5 “C (Gowanloch, 1927). Boyden ef al. (1977) found the dogwhelk in salinities as low as 20-28 ‘&,in the Severn Estuary. A species distribution in nature may be limited, however, by biotic as well as abiotic factors interacting with salinity and temperature. Juvenile dogwhelks tolerated a significantly lower salinity (12.7(2/,) than large snails (15.1X) at 10 “C. However, little biological significance can be assigned to a 2.4& S difference in salinity tolerance. Salinity and temperature affected the J?O: of T. iapillus. At 17.5& 6’0, was depressed but at 20-30s S, PO, did not change. There appears to be little effect of salinity on the oxygen consumption rate of Ttiais spp. at salinities above their low-salinity tolerance limit. T. lumellosa, acclimated to 15x, S, respired at a significantly lower rate than those acclimated to 20, 30, or 40x,, S (Stickle, 1970). T. ~aemast~ma respired at a significantly lower rate at 10 %, S than at 20 or 30 “I, S; their low-salinity tolerance limit is lower than 5% S (Findley ef al., 1978). The rate of oxygen consumption by the dogwhelk was depressed at all salinities
-
21 49 89
0
Day of starvation
Effects of logI CO, regression regression
v
229 f 207 * 187k t45rt
~-
(mg)
P weight
15 14 13 13
-
32 30 27 23
_...._~~_
0.77 0.79 0,74 0.73
k 0.13 k 0.14 + 0.14 10.13
0, consumption (~1 0, .I.____ __log N Snail 138 147 142 161
”
g
‘h -’ )
234 275 305 268
. __-._
Snail
(nM
.~
1.52 k 0.12 1.86 kO.17 1.92+0.17 1.90 rt 0.16
. . . _.-
log a
NH: N excretion _~~~ __. .___ .I
1022 1329 i631 1848
g
’ h -’ )
-_-___
13+ 88 & 63 + 8+
._
._
e 43F 5 430 * I84 360 + 114 SO + 88
PA excretion
1 32 17 II
Snail
-. _.-
14.0 11.7 7.9 8.0
F + + f
fdti0
0:N
1.9 2.2 1.2 0.7
starvation on Tkti~ iupilh at 10°C and 3Oy&, S, values for oxygen consumption rates are calculated from the regression equation = loga + O.&J log U’. where l”O, is given as .uI O? h - ’ and U’ = dry flesh wt in mg; values for NH; excretion rates are calculated from the equation log,,, VNH: = logu t 0.61 log W where c.NH; is given as nM NH’ 4 h -’ : values for primary-amine excretion rates did not fit a equation and are given as nM primary amines. snail _ ’ zkSEand nM PA ‘g-’ ‘h-’ + SE; 0: N ratios are given as the ratio in atomic equivaients of oxygen consumed to NH,f -nitrogen excreted; n = 12.
TAHLF
RESPIRATION
AND NITROGEN
EXCRETION
BY THAIS
13
at 5 “C as shown by low intercept a values and high Q,,, values between 5 and 10 “C. Little predation on Mytilus edulis occurred at 5 “C; in fact, the Scope for Growth (see Bayne, 1975) of the snails was negative throughout the 17.5-350/, salinity range (unpubl. obs.). Bayne & Scullard (1978) also found a winter depression in oxygen consumption by Thais lapillus and concluded that the depression was due to the combined effects of reduced temperature and time since last meal (5-8 days). Snails living at 5 “C are more sensitive to an increase in water temperature at 5-10 “C (Q,” values are 3.7-10.3), than snails living in the rest of their normal temperature range where Q,, values vary from 0.9 to 1.7. Energy losses are minimized as a result of depressed oxygen consumption at low temperature. Bayne & Scullard (1978) point out that the dogwhelk is prepared to respond rapidly to a rise in temperature in the spring; it is, however, less subject to alterations of oxygen consumption rate by temperature changes throughout the rest of the year. Thermal insensitivity (the presence of a thermoneutral zone) throughout a portion of the temperature range has also been reported for the oxygen consumption rate of Littorina irrorata (Shirley et al., 1978). Bayne & Scullard (1978) recommended that a statistical discrimination be made for experimentally derived b values in the equation log PO, = log a + b log W. The common regression exponent, b, was found to be 0.60 f 0.07 (SD) in our experiments. This value is not statistically different from the b value of 0.51 that was derived for Thais lapillus by Bayne & Scullard (1978). Stickle (1973) found b values ranged from 0.2 to 1.0 with a mean value of 0.60 in T. lamellosa. The f0, values obtained in our study compare closely with those obtained by other authors. The PO? for a 250-mg snail ranged from 10 ~10, . h-’ at 5 “C and 17.5 y&,S to 60 ~1 0, . h -’ at 20 “C and 20 %,, S. Bayne & Scullard (1978) reported a winter (9-14 “C) QO, of 61 and a summer (15-20 “C) value of 88 ~1 0, . h-’ for a 250-mg dogwhelk from the same population. Sandison (1966) reported a mean PO, of 55 ~1 0, . h-’ for a 250-mg dogwhelk at 18 “C. Ammonia excretion rates were less affected by temperature than t0, as judged by Q,, values. In addition, pNH,+ did not vary as a function of salinity at 5 “C nor did it vary systematically with salinity at 10, 15 or 20 “C. This tinding is probably due to the protein-oriented catabolism of T. lupillus. PNH: varies as a function of salinity in stepwise-acclimated T. lapillus in a different pattern from that observed in T. lamellosa or T. emarginatu. Stickle (1970) found the ammonia excretion rate of T. lamellosa to be significantly lower at 15 X S than at 20, 30 or 40 %, S. Emerson (1969) found the ammonia excretion rate of T. lamellosa to be significantly higher in 100% sea water (= 35 y&,s) than in 50 or 150% sea water after 1 wk at each salinity. He found, however, no significant difference in the ammonia excretion rate in T. emarginata in 100 and 50% sea water after 1 wk in each salinity. Net flux rates of primary amines across the body surface of T. lapillus indicate a loss of primary amines from the snail. Assays were carried out at ambient-water
14
primary
W. B. STIC‘KLL
amine
concentrations
AI\;D
of 0.6-5.5
B 1. BAL Nk
PM. This primary-amine
loss from
the
dogwhelk accounts for a significant percentage of excreted nitrogen. Primary-amine loss varied from 7 to 41”/, of ammonia excretion in T. lupillus. Relatively more amino-N was excreted at 17.5”/, S than at all other salinities. Bayne & Scullard (1977) have shown seasonal and habitat differences in the relative amounts of primary amine and ammonia excreted by three species of Mytilus. Conover & Corner (1968) gave a theoretical minimum value of 8 for the 0 : N ratio if only protein is catabolized, but Mayzaud (1973) calculated 0 : N ratios of 4.4 for mammalian proteins and 2.3 for Calanus jinmarchicus proteins. Thuis lupillus predominately catabolizes protein as shown by 0: N ratios which varied between 4.2 and 13.1, when nitrogen excreted was the sum of ammonia and primary amines; 5.9 and 15.6 when ammonia is considered the only nitrogen species excreted. Stickle (1975) estimated that a female T. Iamellosa received 94’1/,, of its energy from protein catabolism during aggregation for reproduction, and 6% from carbohydrate catabolism. Temperature and temperatureesalinity interaction affected 0 : N ratios in our study; the 0 : N ratios were significantly higher at 15 “C than at 5, 10, and 20 “C and significantly lower at 5 “C than at 10, 15, or 20 “C. Oxygen: nitrogen ratios appear to be higher in herbivores than in carnivores. probably reflecting the nitrogen-rich diet of carnivores. For example. Conover & Corner (1968) divided the copepods they studied into a herbivore group consisting of Calanus and near relatives and an omnivore-carnivore group consisting of the Mctridiu-Parenchaeta group. Carnivores had higher respiration and excretion rates than herbivores, with lower 0: N ratios that cycled less seasonally. The herbivore Mytifus edulis in unstressed conditions frequently exhibits 0 : N ratios >40. The 0 : N ratio of the herbivorous sea urchin Strongylocentrotus drohachiensis (0. F. Miiller) at 30 &, S and 13 “C is 38 (unpubl.). Capuzzo & Lancaster (1979) found the 0 : N ratio of Homurus americanus larvae fed on brine shrimp to indicate principally protein catabolism (x 28) and to decline to = 23 during the last two larval
stages
indicating
even
more
reliance
on protein
as a metabolic
substrate.
Unpublished data from our laboratory have shown the 0 : N ratio of Thai.7 haemastoma (Linne) at 30°C and 30”/, .S to be 7.7 and that of T. lima (Cimelin) at 30ym S and IO’< to be 16.0. Information gathered to date indicates that unstressed herbivores have high 0 : N ratios ( > JO), whereas carnivores exhibit low 0 : N ratios. Long-term starvation (89 days) had ;I significant effect on oxygen consumption and nitrogen excretion of T. lapifhrs. Although the rate of oxygen consumption by snails declined by 2X”,, during the 89 days without food, this decline was more than accounted for by a 37”,, decline in tissue weight. No change occurred in the recalculated intercept (J and the weight-specific respiration rate incrctlscd by 17”,, (Table VI). Bayne & Scullard (1978) noted the oxygen consumption rate of 7‘. lupiilzrs declined during 18 days starvation and also found a decline in the intercept value. a. with starvation. Different patterns in the change of ox!‘-en consumption
RESPIRATION
AND NITROGEN
EXCRETION BY THAIS
15
rate with starvation in the two studies may have been due to two causes. First, whereas all snails in the study of Bayne & Scullard (1978) had just fed when the starvation studies began, giving a uniformly high rate of oxygen consumption, snails used in the present study were at all stages of the feeding cycle at the beginning of the starvation experiment. This difference in methodology would have the effect of lowering the control respiration rate in our study. Secondly, Bayne & Scullard (1978) did not note any change in the locomotory activity pattern of T. lapillus during the 18 days’ starvation. We observed increased crawling by the snails in the Gilson vessels during our longer-term starvation study. Calow (1972) has also noted increased crawling in some snails during starvation. Stickle & Duerr (1970) and Stickle (1971) found constant or increased rates of weight-specific oxygen consumption by T, lamellosa during 53 and 91 days starvation. Ammonia excretion by T. lapillus increased throughout the starvation period of the dogwhelk, whereas the primary-amine loss rate increased to Day 21 and declined to control levels by Day 89. Consequently, the 0: N ratio indicated that the catabolism of protein for energy during starvation met almost all of the snails energy needs. This finding is not surprising, for protein constitutes the majority of the body in muricids such as T. haemastoma (Belisle & Stickle, 1978) and T. lamellosa (Stickle, 1975). ACKNOWLEDGEMENTS
W. Stickle gratefully acknowledges Louisiana State University for granting him a sabbatical leave which allowed him to do this work. Special thanks go to Mr. R. Glover, Director of the Institutk for Marine Environmental Research (IMER), for providing the opportunity to work at IMER. It was indeed a pleasure to interact with all involved in the experimental ecology programme. Special thanks go to Dr. J. Widdows, and to Miss M. Day for performing some of the oxygen consumption and nitrogen excretion experiments.
REFERENCES BAYNE,B. L., 1975. Aspects of physiological condition in Mytilus edulis L., with special reference to the effects of oxygen tension and salinity. In, Proc. 9th Eur. Mar. Biol. Symp., edited by H. Barnes, Aberdeen University Press, Aberdeen, pp. 213-238. BAYNE, B.L. & C. STULLARD,1977. Rates of nitrogen excretion by species of Myrilus (Bivalvia: Mollusca). J. Mar. Biol. Assoc. U.K., Vol. 57, pp. 355-369. BAYNE,B. L. & C. SCULLARD,1978. Rates of oxygen consumption by Thais (Nucella) lapillus (L.). J. Exp. Mar. Biol. Ecol., Vol. 32, pp. 97-I 11. BELISLE,B. W. & W. B. STICKLE,1978. Seasonal patterns in the biochemical constituents and body component indexes of the muricid gastropod, Thais haemastoma. Biol. Bull. (Woods Hole, Mass.), Vol. 155, pp. 259-272. BOYDEN,C. R., J. H. CROTHERS,C. LITTLE & C. METTAM,1977. The intertidal invertebrate fauna of the Severn Estuary. Field Stud., Vol. 4, pp. 477-554.
16
W. B. STICKLE
AND
B. 1.. BAYNt
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