Seasonal changes in organic composition and caloric content of an Arctic marine amphipod, Onisimus (= Boeckosimus) affinis H.J. Hansen

J. exp. mar. Biol. Ecol., 1979, Vol. 40, pp. 183-192 0 Elsevier/North-Holland Biomedical Press

SEASONAL CALORIC

CHANGES CONTENT

ONISIMUS

(=

IN ORGANIC

BOECKOSIMLJS)

J. A. Arctic Biological Station, Department qf

COMPOSITION

OF AN ARCTIC MARINE

AND

AMPHIPOD,

AFFINIS H. J. Hansen

PERCY

Fisheriesand Oceans, P.O. Box 400, Ste Anne de Bellevue, P.Q., Canada H9.Y 3L6

Protein, lipid, carbohydrate, chitin, ash, and caloric energy contents of the Arctic marine benthic amphipod Onisimus (= Boeckosimus) ajfhis H. J. Hansen were determined at intervals over two and one half years. The lipid content exhibited the most pronounced seasonal change, from a minimum of about 14-17% of dry wt to a maximum of 25527% of dry wt. An increase in lipid content in the spring coincided with the reproductive period of the species. Lipid and caloric content decreased during the summer to levels that were maintained through the winter, indicating that the animals do not store significant nutritional reserves for use during the winter. The dry weight proportions of other components were: protein 27.7-38.3x; carbohydrate 1%4.0%; chitin 7%8.2%; ash 21.3-27.2%. Caloric Content varied between 3.29 and 4.18 cal/mg dry wt. Abstract:

INTRODUCTION

The organic composition of marine organisms may vary markedly during the year, reflecting both nutritional and reproductive cycles. Such fluctuations in crustaceans have been studied most often in species inhabiting temperate seas (Fisher, 1962; Barnes et al., 1963; Heath & Barnes, 1970; Raymont et al., 1971; Barnes, 1972; Bimstedt, 1976), although in recent years several comparable studies have been carried out on Antarctic species (Littlepage, 1964; Ferguson & Raymont, 1974; Rakusa-Suszczewski & Dominas, 1974; Clarke, 1977). With the exception of planktonic copepods (Lee et al., 1972; Lee, 1974) Arctic species have been ignored in this regard. High latitude ecosystems are of considerable interest from an energetics viewpoint because they are characterized by extreme seasonal oscillations in primary production. Energy input into the system occurs as widely spaced, abbreviated, relatively intense pulses of primary production, while subsequent utilization of the captured energy by herbivores and carnivores must be spread over the whole year. Different behaviour may be adopted by polar marine organisms to compensate for the pronounced fluctuations in energy availability. Some, such as the planktonic herbivores Euphausia crystallorophias and Calanus hyperboreus accumulate a large lipid reserve during the summer phytoplankton bloom and then utilize it during the subsequent winter (Littlepage, 1964; Lee, 1974). 183

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J.A.PERCY

The carnivorous Arctic copepod Metridia longa shows a similar seasonal fluctuation in nutritional reserves (Lee et al., 1972). In contrast, the predatory Antarctic copepod Euchaeta antarctica is able to maintain a relatively high lipid content through much of the year and during the winter levels rise even higher as a result of the production of large fat laden eggs (Littlepage, 1964). Many benthic crustaceans of polar seas are omnivorous scavengers or opportunistic feeders (Arnaud, 1977) and are thus not so directly dependent upon the phytoplankton bloom as are planktonic species. The benthic decapod Chorismus antarcticus does not accumulate lipid reserves prior to the winter; being a scavenger it is probably not subjected to extended periods without food (Clarke, 1977). In contrast, in the Antarctic benthic amphipod Paramoera walkeri the highest lipid values were in late summer and then declined steadily during the winter until the animals began feeding on the sub-ice microflora in the spring (Rakusa-Suszczewski & Dominas, 1974). It has been suggested that other polar species may pass through the winter in a dormant or vegetative state, characterized by a marked reduction in the rate of physiological processes (Arnaud, 1977). Such a response would clearly minimize the need for extensive nutritional reserves. Such winter torpor has been shown in some temperate crustaceans (Edwards & Irving, 1943) but has not yet been convincingly demonstrated in polar species. It is not yet known whether benthic crustaceans in the Arctic are able to obtain sufficient food continuously through the long winter, must rely upon accumulated reserves, or simply exist in a torpid state for several months. The present study examines seasonal changes in gross biochemical composition and caloric content of the Arctic marine benthic amphipod, Onisimus (= Boeckosimus) affin0 H. J. Hansen.

MATERIALSANDMETHODS

Animals were collected at intervals in baited traps set in 20 m of water in the Eskimo Lakes (69”25’N : 131”16’W), a series of marine embayments to the east of the Mackenzie Delta in the Northwest Territories. A brief description of the collecting site may be found in Percy (1975). Summer and winter samples were collected at the same site, the latter through about 2 m of ice. Animals were transported to the laboratory in sea water, held for several hours without food, rinsed in distilled water and dried at 60 “C for 24 h. The dried samples were stored at -20 “C until analysed. Subsamples were taken from a summer (August) and mid-winter (February) collection for a determination of the length-dry weight relationship. Total fresh body length (from tip of rostrum to end of telson) was measured, using an upright projector of the type designed for reading fish scales. Dry weights (60 “C for 24 h) and ash weights (after ignition at 550 “C for 12 h) were determined.

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185

The biochemical analyses were carried out on coarsely ground subsamples containing one or more animals, depending upon size and estimation requirements. The proportions of the various components are expressed as a percentage of the total dry tissue weight. Total lipid was determined gravimetrically following microsoxhlet extraction with chloroform-methanol (2 : 1 v/v) for 68 h, using samples of 500-100 mg dry wt. The extract was dried to constant weight at 60°C. Total carbohydrate was determined spectrophotometrically with anthrone reagent following digestion of 10 mg subsamples in hot trichloroacetic acid. Results are expressed as glucose equivalents. Total nitrogen was determined by micro-Kjeldahl analysis, essentially as outlined by Barnes (1959) using x 50-mg samples. Protein was estimated by multiplying the total nitrogen content by 6.25. Chitin was measured in only one series of summer samples (August) and one series of mid-winter samples (February), using a gravimetric method similar to that of Bamstedt (1974). The caloric content of pelletized l&20 mg samples was determined with a Phillipson microbomb calorimeter.

RESULTS

Length-weight relationship

The relationship between total dry weight and body length of 0. affiis during the late summer (August) and mid-winter (February) are shown in Fig. 1. The regression equations for dry weight ( W, mg) on body length (L, mm) are : summer: log W= 2.71 log L - 2.11 (r2 = 0.94, N= 212), winter : log W = 2.83 log L - 2.23 (r’ = 0.92, N = 93). The regression lines are not significantly different (P > O.OS), indicating that there is little, if any difference in body weight of summer and winter animals of comparable size. The corresponding regression equations for ash-free weight (W, mg) on body length (L, mm) are: summer: log W= 2.80 log L - 2.42 (r’ = 0.92, n = 216), winter : log W = 2.87 log L - 2.33 (r’ = 0.88, IZ= 98). Relatively few juveniles were present in winter samples, and all were > 7 mm in length. In contrast, during August large numbers of 5-7 mm long juveniles were caught. The largest animals collected during the entire study were ~20 mm in length. Animals larger than about 16 mm were invariably female.

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b

BODY

Fig.

1. Relationship collected

Biochemical

LENGTH

(mm)

between dry weight and body length of male, female and juvenile Onisimus during the summer (a, 31st Aug.) and during the winter (b, 28th Feb.).

uffinis

composition

The seasonal changes in relative proportions of protein, lipid, carbohydrate, and ash, and in the total caloric content of 0. affinis are illustrated in Fig. 2. In some instances analyses were conducted on samples consisting solely of gravid females. The protein content varied between 27.7 and 38.3% of dry weight (Fig. 2). The amount remained fairly uniform throughout the year except for a slight decrease during the June-July period. In both years this transitory decline in protein content coincided with a rise in lipid level. The protein content of gravid animals was only slightly higher (l-2%) than that of non-gravid ones. Protein.

The mean lipid content varied between 14.0 and 27.0% (Fig. 2). Through much of the year the lipid level remains fairly uniform at about 15-20x of dry weight. The levels observed in mid-winter are not significantly lower than those observed in late summer. In fact, in all three years, the February-March lipid values are consistently about 5% higher than the late summer values. During the Lipid.

SEASONAL

Jo

CHANGES

IN AN ARCTIC

AMPHIPOD

187

LIPID

I

CARBOHYDRATE

30

TASH

6

___---~--__-_--~-(::r,-__ ___-----

\

E”

-z *

3

/ A’S’O’N’D

Fig. 2. Seasonal value (expressed

J’F

M'A

11

J

J’A

S

0

N

D

J

F

u

A

M

J

J

A’

’ SONDJ

FM

changes in the percentage organic composition (expressed as y0 of dry wt) and caloric as cal/mg) of Onisimus affitzis: Cl, brooding females; vertical lines indicate standard deviations.

May-July period there was a transitory rise in lipid content to 25-30x of dry weight. By August the lipid levels had decreased to about the early spring values. Gravid females sampled between May and July had a lipid content only slightly higher (l-3”/,) than that of the general population. Carbohydrate. The carbohydrate content remained uniformly low throughout the sampling period, varying between 1.8 and 4.0% of dry weight. There were no detectable seasonal trends in carbohydrate content. Gravid and non-gravid animals contained similar amounts. Chitin. The chitin content was only measured on two occasions during the study. In late summer (9th August) chitin accounted for 8.2% (range = 7.8-8.6x; S.D. =

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J. A. PERCY

0.2; n = 8) of the dry body weight, while in mid-winter

(26th February) it made up 7.87; (range = 7.68.3%; S.D. = 0.2; n = 8) of the dry weight. These values are significantly different (P < 0.005, t = 3.74).

Ash. The ash content

varied between 21.3 and 27.2% of the dry weight (Fig. 2). The level remained fairly constant throughout the year except for a slight decline of about 5”/, during May-June. Late summer and mid-winter samples were not significantly different. The levels of ash in gravid and non-gravid animals were comparable. Calories. The mean caloric content varied between 3.29 and 4.18 cal/mg dry wt (Fig. 2). The caloric value remained fairly constant at about 3.6 cal/mg during much of the year, except during the May-June period when it rose to about 4.2 cal/mg. Gravid animals had a significantly higher caloric content than non-gravid ones and it was the presence of these gravid animals during the May-June period that primarily accounted for the increase in caloric content of the population at that time, Animals collected in mid-winter had a caloric content that was similar to that of animals collected in late summer.

DISCUSSION

The protein content of ~n~simus (28-38x of dry wt) is low compared with that of many amphipods, in which values of about 50% are common (Omori, 1969; Green, 1971; Geng, 1925). Even higher proportions have been reported for other marine crustaceans (Raymont et al., 1964; Ikeda, 1971). The protein content of ~nisimus has been calculated from total nitrogen and will include some non-protein components. Recent determinations using a calorimetric estimation indicate that the protein accounts for at least 91% of the total nitrogen in Onisimus. The protein level of Onis~mus is strikingly similar to that reported for the Antarctic benthic amphipod Paramoeru waikeri (Rakusa-Suszczewski & Dominas, 1974). The lipid content of Onisimus, ranging from 14 to 27”/, of the dry weight, lies close to the middle of the range reported for other species of amphipods. Values as low as 5.9 and 7.7% of dry weight have been measured in ~urnrn~rus puiex and Carinogammarus roeselii, respectively (Geng, 1925). Lipid values as high as 53% of dry weight have been reported for the Antarctic amphipod, Orchomonella plebs (Pearse & Giese, 1966). The lipid content of the Antarctic Pffr~rnoer~ walkeri decreased to < Su/,of dry weight following release of the young. During the early winter the level rose again to about 15x, a value comparable with the minimal value found for Onisimus (Rakusa-Suszczewski & Dominas, 1974). The carbohydrate content of marine crustaceans is generally very low and does not appear to represent a significant nutritional reserve (Raymont & Conover, 1961).

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CHANGES

IN AN ARCTIC

AMPHIPOD

189

Ikeda (1971) obtained values ranging from 0.5 to 3.17; of dry weight for a variety of planktonic species from the Bering Sea. The carbohydrate content of many amphipods (Raymont & Conover, 1961; Ikeda, 1971; Rakusa-Suszczewski & Dominas, 1974) including that of Onisimus, is comparable with the values reported for planktonic forms. Exceptionally high values reported for Gammarus pulex and Curinogammarus roeselii (12.5 and 21.3% of dry wt, respectively; Geng, 1925) must be regarded with skepticism. Information about the chitin content of amphipods is limited. The value of 7.8-8.2x of dry weight obtained in the present study compares fdvourably with the 5.0--9.7x reported for the Antarctic Paramoera walkeri (Rakusa-Suszczewski & Dominas, 1974). In contrast, the planktonic Euthemisto lihellulct has < 5:!/ chitin (Ikeda, 1971). In Pandalus borealis chitin ranged from 4.5-9.0x (Bamstedt, 1974) while in Neomysis it made up 7.1% of the dry weight (Raymont et al., 1964). In contrast, Thysanoessa raschi had 2.8% chitin (Ikeda, 1971), Maganyctiphunes norvegica, 4.2% (Raymont et al., 1971), and Euphausia superba 3.3-5.7x (Ferguson & Raymont, 1974). Four species of copepods from the Bering Sea had chitin contents ranging from 2.1-3.5% (Ikeda, 1971). Clearly, the chitin content of Onisimus lies near the upper part of the range from the smaller marine crustaceans. A considerable amount of information about the ash content of marine crustaceans is available, much of it collected in conjunction with caloric studies. Values vary from a low of x 5% of dry weight in some species of calanoid copepods (Ikeda, 1971) to 46.4% in adults of the decapod Cullinectes sapidus (Thayer et al., 1973). The ash content of Onisimus, 21-27x of dry weight, lies near the middle of the range of values for amphipod species. This range extends from 9.376 in Parathemisto sp. (Nakai, 1955) to 37-43x for mixed benthic amphipods collected in the western Arctic (Atkinson & Wacasey, 1976). The ash content of the Antarctic Paramoera walkeri (Rakusa-Suszczewski & Dominas, 1974) is almost identical to that of Onisimus. Data on the caloric content of crustaceans has been accumulating rapidly. In the extensive tabulation of Cummins & Wuycheck (1971) values reported for a number of crustacean species range from 1780 to 5877 Cal/g dry wt. In some instances, caloric values were indirectly obtained by calculation from gross biochemical composition, using standard oxycaloric coefficients or by wet oxidation of the organic component. Bomb calorimetry has now largely superseded the indirect techniques. The caloric value for Onisimus (3290-4180 Cal/g) lies close to the mid point of the range of values reported for various amphipods. The lowest values recorded were for Leptocheirus pinguis (2319-3348 Cal/g) (Tyler, 1973) and the highest for Parathemisto sp. (5807 Cal/g) (Nakai, 1955). The highest value obtained by bomb calorimetry was 4741 Cal/g for Pontoporeia affinis (Green, 1971). Once again, the range of values reported for the Antarctic Paramoera walkeri (2800-4200 Cal/g) (RakusaSuszczewski & Dominas, 1974) is virtually identical to the seasonal range found in Onisimus affinis.

190

J. A. PERCY

In those species so far studied the most significant seasonal changes have been found in the lipid and protein contents. In the present study there appears to be an inverse relationship between the two, the proportion of protein decreasing as that of lipid increases. Raymont et al. (1969) noted a similar reciprocal relationship between the two fractions and suggested that they may serve as complementary substrates. The apparent reciprocal relationship may not, however, be real. As Bamstedt (1976) has pointed out one of the drawbacks of expressing the results as proportions rather than as absolute weights is that some components may only appear to decrease as a consequence of an actual increase in another component. Seasonal cycles in lipid content of polar organisms may reflect different processes. In some, lipid is rapidly accumulated at the time of peak food availability and is then gradually utilized for metabolic purposes during the extended period of food scarcity. In others, the rise in lipid may be associated primarily with the synthesis of reproductive products. The direct storage of lipid reserves should be most pronounced in those organisms whose food supply is highly seasonal and relatively specific, and less so in those species with food consistently available throughout the year. Herbivorous zooplankton clearly fall into the former category and several have been shown to attain maximum lipid levels in late summer, followed by a gradual decrease through the winter to a minimum just prior to the summer phytoplankton bloom (Lee, 1974; Littlepage, 1964; Mauchline & Fisher, 1969). In contrast, some carnivorous zooplankton do not store large reserves of lipid during the summer, and appear to be able to obtain sufficient food continuously through the winter. Many species of benthic crustaceans in the Arctic are omnivorous scavengers and these also are probably able to secure adequate quantities of food throughout the winter. This appears to be the case with 0. ~~~~~~.There is no evidence of a si~i~cant accumulation of nutritional reserves during the late summer. Although the winter sampling was of necessity limited, it is nevertheless clear that there was no marked decrease in organic reserves during the course of the winter. Protein, lipid, and carbohydrate levels in late February were not significantly different from those found in late August. Similarly no significant differences were found in either the caloric content or in the regression of total dry body weight on body length of animals collected at these times. A significant rise in lipid levels occurred during the early summer. It seems likely that given the surge of biological activity in the water column at this time that the quantity and possibly the quality of the food available to these benthic scavengers increases signi~cantly. In addition, reproduction occurs during this same period. Large numbers of gravid females appear in the population during late May, June, and July with a small percentage occasionally persisting into early August (unpubl. data). The rise in lipid content coincides with this peak of reproductive activity and once reproduction finishes the lipid decreases to its former level, which is maintained throughout the winter. Similarly, Clarke (1977) found no evidence of a seasonal variation in the lipid content of the Antarctic decapod C~oris~u~ antarcticus,

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apart from those changes directly associated with reproduction. This species is also an omnivorous benthic scavenger that is unlikely to be faced with prolonged food shortages. The fact that large numbers of active animals were readily caught in baited traps in mid-winter clearly indicates that Onisimus does not merely exist through the winter in a vegetative or torpid state, but scavenges actively throughout the year.

ACKNOWLEDGEMENTS

I wish to thank Mr J. Walbridge for his able technical assistance in many aspects of this study. Many other members of the technic31 staff of the Arctic Biological Station were particularly helpful during field operations and their cooperation is much appreciated.

REFERENCES

ARNAUD, P.M., 1977. Adaptations within the antarctic marine benthic ecosystem. In, Aduptufions within Anfarcric ecosystems, edited by G. A. Llano, Smithsonian Institution, Wash. D.C., pp. 135-157. ATKINSON, E.G. & J. W. WACASEY, 1976. Caloric values of zoobenthos and phytobenthos from the Canadian Arctic. Fish. Mar. Serv., Tech. Rep., No. 632, Environment Canada, 24 pp. BAMSTEDT, U., 1974. Biochemical studies on the deep-water pelagic community of Korsfiorden. western Norway. Methodology and sample design. Sursia, Vol. 56, pp. 71-86. BAMSTEDT, u., 1976. Studies on the deep-water pelagic community of Korsfjorden, western Norway. Changes in the size and biochemical composition of Meganyctiphanes norvegica (Euphausiacea) in relation to its life cycle. Sarsia, Vol. 61, pp. 15-30. BARNES, H., 1959. Appururus and methods qf oceanography. 1. Chemical. George Allen & Unwin, London, 341 pp. BARNES, H., 1972. The seasonal changes in body weight and biochemical composition of the warmtemperate cirripede Chthalamus stellatus (Poli). J. exp. mar. Biol. Ecol., Vol. 8, pp. 89-100. BARNES, H., M. BARNES & D. M. FINLAYSON, 1963. The seasonal changes in body weight, biochemical composition and oxygen uptake of two common boreoarctic cirripedes Balanus halunoides (L.) and B. balunus (L.) da Costa. J. mar. biol. Ass. U.K., Vol. 43, pp. 185-211. CLARKE. A., 1977. Seasonal variations in the total lipid content of Chorhmus antarcticus (Pfeffer) (Crustacea: Decapoda) at South Georgia. J. exp. mar. Biol. Ecol., Vol. 27, pp. 93-106. CUMMINS, K. W. &J. C. WUYCHECK, 1971. Caloric equivalents for investigations in ecological energetics. Int. ver. theor. angew. Limnol. Verh., Vol. 18, pp. l-158. EDWARDS, G.A. & L. IRVING, 1943. The influence of season and temperature upon the oxygen consumption of the beach flea, Talorchesria megalopfhalma. J. ceil. romp. Physiol., Vol. 21, pp. 183-189. FERGUSON, C. J. & J. K. B. RAYMONT, 1974. Biochemical studies on marine zooplankton. XII. Further investigations on Euphausiu superba Dana. J. mar. biol. Ass. U.K., Vol. 54, pp. 719-725. FISHER, L. R., 1962. The total lipid material in some species of marine zooplankton. Rupp. P.-v. Rtun. Cons. perm. int. Explor. Mer, Vol. 153, pp. 129-136. GENCI, H., 1925. IV. Der Futterwert der naturlichen Fischnahrung. 2. F&h., Vol. 23, pp. 137-165. GREEN, R. H., 1971. Lipid and caloric contents of the relict amphipod Pontoporeiu qffinis in Cayuga Lake, New York. J. Fish. Res. Bd Can., Vol. 28, pp. 776-777. HEATH, J. R. & H. BARNES, 1970. Some changes in the biochemical composition with season and during the moulting cycle of the common shore crab, Carcinus muenas (L). J. exp. mar. Biol. Ecol., Vol. 5, pp. 199-233. IKEDA, T., 1971. Chemical composition and nutrition of zooplankton in the Bering Sea. In, Biological

192

3. A. PERCY

oceanography qf’ the northern North Pacific Ocean. edited by A. Y. Takenouti, ldemitsu shoten, Tokyo, pp. 433-442. LEE, R. F., 1974. Lipid composition of the copepod Culanus hyperhoreus from the Arctic Ocean. Changes with depth and season. Mar. Biol., Vol. 26, pp. 313-318. LEE, R.F., J. HIRATA, J.C. NEVENZEL, R. SAUERHEBER & A.A. BENSON. 1972. Lipids in the marine environment. Cal$ mar. Res. Comm. CalCOFl Rep., Vol. 16, pp. 95-102. LITTLEPA~;E, J. L., 1964. Seasonal variation in lipid content of two antarctic marine Crustacea. In, Antarcfic biology, edited by R. Carrick, M. Holdgate & J. Prtvost, Hermann, Paris, pp. 463-470. MAUCHLINE, J. & L. R. FISHER, 1969. The biology of euphausiids. Adv. mar. Biol., Vol. 7, 454 pp. NAKAI, Z., 1955. The chemical composition, volume, weight and size of the important marine plankton. Tokai Reg. Fi.rh. Res. Lab., Spec. Puhl. No. 5. pp. 12-24. OMORI, M., 1969. Weight and chemical composition of some important oceanic zooplankton in the North Pacific Ocean. Mar. Biol., Vol. 3, pp. 410. PEAKS~, J. S. & A. C. GIESE, 1966. The organic constitution of several invertebrates from McMurdo Sound, Antarctica. Comp. Biochem. Physiol., Vol. 18, pp. 47-57. PFRCY, J. A., 1975. Ecological physiology of arctic marine invertebrates. Temperature salinity relationships of the amphipod Onisimus qjfinis H. J. Hansen. J. up. mar. Biol. Ecol., Vol. 20, pp. 99-117. RAKUSA-SUSZ~ZEWSKI, S. & H. DOMINAS, 1974. Chemical composition of the antarctic amphipoda Purumowu wcrlkwi Stebbing and chromatographic analysis of its lipids. Polskie Archwm Hydrohiol., Vol. 21, pp. 261-268. RAYMONT, J. E.G. & R. J. CONOVER, 1961. Further investigations on the carbohydrate content of marine zooplankton. Limnol. Ocecmogr., Vol. 6, pp. 154164. RAYMONT, J. E.G., J. AUSTIN & E. LINFORD. 1964. Biochemical studies on marine zooplankton. 1. The biochemical composition of Neomysis integer. J. Cons. perm. inl. Explor. Mer, Vol. 28, pp. 35&363. RAYMONT, J. E.G., R.T. SRINIVASACAM & J.K.B. RAYMONT, 1969. Biochemical studies on marine zooplankton. VII. Observations on certain deep sea zooplankton. Int. Rev. ges. Hydrohiol., Vol. 54, No. 3, pp. 357-365. RAYMONT, J. E.G., R.T. SRINIVASAGAM & J.K. B. RAYMONT, 1971. Biochemical studies on marine zooplankton. VIII. Further investigations on Meganyctiphunes norwgica (M. Sars). Deep-Sea Res., Vol. 18, pp. 1167-l 178. THAYFR, G. W., W. E. S~HAAF, J. W. ANC~ELOVIC& M. W. LACROIX. 1973. Caloric measurements of some estuarine organisms. Fishery Bull. NOAA, Vol. 71, pp. 289-296. TYLER, A. W.. 1973. Caloric values of some north Atlantic invertebrates. Mar. Biol., Vol. 19, pp. 258.-26 I.