Effect of the receding ice-edge on the condition of mid-water fishes in the northwestern Weddell Sea: results from biochemical assays with notes on diet

Electrona antarctica and Bathylagus antarcticus are dominant fishes in the Southern Ocean pelagic ecosystem with disparate life histories, making them excellent subjects for comparative studies. Twenty-one indices of nutritional condition were compared in both species by observing changes in each index as it varied spatially and temporally in association with the marginal ice-zone bloom in the northwestern Weddell Sea. E. antarctica and B. antarcticus exhibited very different patterns of response to the bloom. Nutritional condition increased in 11 of 21 measures in E. antarctica, suggesting that it was in poorer condition at ice-covered stations and in greatly improved condition in post-bloom, open-water stations. The data, combined with a few observations of larvae, indicate that E. antarctica increases feeding before the spring bloom, rapidly building stores of lipid, which are probably used for spawning. In contrast, only three measures of condition were variable in B. antarcticus, and lipid actually decreased from ice-covered to open water. RNA:DNA values increased in open water, coinciding with an increase in food volume present in their guts. These observations, coupled with observations of larvae in ice-covered stations, suggest that B. antarcticus possesses sufficient energetic stores to spawn prior to the bloom, so that larvae are able to fully utilize available resources associated with the spring bloom. Increased somatic growth, as indicated by RNA:DNA, may not begin until later, when the bloom was beginning to decline. Earlier work, which suggested that the deeper living, non-migrating species, like B. antarcticus, would not be affected by the bloom until after shallower, migratory species, like E. antarctica, is supported. Of the assays tested, RNA:DNA appeared to be the most sensitive. The combined assessment of many measures including biochemical, compositional, dietary, and age estimates from single specimens is possible if the samples are treated with sufficient care. The reliance upon a single measure to help interpret the ecology of a species, especially in nekton-sized species, is not as effective as techniques used in combination. Received: 12 January 2000 / Accepted: 16 August 2000     

Genetic homogeneity and circum-Antarctic distribution of two benthic shrimp species of the Southern Ocean, Chorismus antarcticus and Nematocarcinus lanceopes

During the last years, molecular studies revealed significant population differentiation and cryptic species within various benthic and pelagic marine Antarctic taxa. This is unexpected due to the lack of obvious barriers to gene flow and strong current systems. Using mitochondrial (COI, 16S rDNA) and nuclear (28S rDNA: D2) gene fragments, we tested whether two circum-Antarctic benthic shrimps with planktotrophic larvae, Chorismus antarcticus and Nematocarcinus lanceopes, show patterns of regional differentiation. For both species, the 16S and the 28S fragment were invariant. However, for COI we found 24 different haplotypes for Chorismus antarcticus and 54 for Nematocarcinus lanceopes. No significant differentiation was observed among populations or regions. Furthermore, we found signatures of a population expansion in the late Pleistocene hinting at an impact of large-scale glaciations in particular on the shallow-water shrimp Chorismus antarcticus, supporting a (re)colonization and demographic expansion of this shrimp species in response to climate oscillation.     

Mitochondrial cytochrome b variation in sleeper sharks (Squaliformes: Somniosidae)

Sleeper sharks are a poorly studied group of deep-sea sharks. The subgenus, Somniosus, contains three morphologically similar species: S. microcephalus found in the Arctic and North Atlantic; S. pacificus in the North Pacific; and S. antarcticus in the Southern Ocean. These sharks have been reported mainly in temperate to polar waters and occasionally in subtropical locations. They have not been recorded in tropical waters. This study investigates the relationships among the accepted species of Somniosus through analysis of mitochondrial cytochrome b sequence variation. Seventy-five samples were examined from four sampling locations in the North Pacific, Southern Ocean and North Atlantic. Twenty-one haplotypes were found. A minimum spanning parsimony network separated these haplotypes into two divergent clades, an S. microcephalus and an S. pacificus/antarcticus clade, strongly supporting the distinction of S. microcephalus as a separate species from the Pacific sleeper shark species. Analysis of genetic structure within the S. pacificus/antarcticus clade (analysis of molecular variance, allele frequency comparisons, and a nested clade analysis) showed limited or no differences amongst three populations. Further examination of genetic variation at more variable mtDNA and nuclear markers is needed to examine the species status of S. pacificus and S. antarcticus.     

The trophic link between squid and the emperor penguin <Emphasis Type="Italic">Aptenodytes forsteri</Emphasis> at Pointe Géologie,Antarctica

Cephalopod beaks retrieved from stomachs of dead emperor penguin chicks at Pointe Géologie, Terre Adélie, provide information on taxonomic and size composition of the penguin’s squid diet, on the trophic range of the squid species preyed upon and on the fractional trophic impact of the penguin on the whole food web. Emperor penguins prey upon four squid species (Psychroteuthis glacialis, Kondakovia longimana, Gonatus antarcticus, Alluroteuthis antarcticus) and do not take squid larger than 480 mm mantle length. Larger squid live either below the penguin’s diving range or are beyond its handling capacity. Nitrogen stable isotope ratios indicate that squids cover a range of about two trophic levels (2.5–8‰ δ¹⁵N). The impact of the emperor penguin, however, concentrates on the upper part of this range, about 68% of its squid prey being >6‰ δ¹⁵N. The principal components of the emperor’s diet, fish, krill and squid, differ distinctly in average trophic level. Consequently the trophic position of the emperor penguin changes accordingly with diet composition and may differ by almost one trophic level between different emperor penguin colonies.     

Reproductive biology in two species of deep-sea squids

Deep-sea squids, Moroteuthis ingens and Gonatus antarcticus, were collected in the slope waters off the Falkland Islands and their reproductive systems preserved and investigated onshore. Changes in oocyte length-frequencies at maturation and spawning, and their fecundity were studied. These squids, as well as many other species, are characterised by a synchronous oocyte growth and ovulation. Oviducts are not used for ripe egg accumulation and consequently the universal scale of Lipinski (1979) cannot be applied to assign female maturity. M. ingens spawns near the bottom; its fecundity is 168–297 thousand eggs. Maximum egg size is 1.8–2.7 mm. G. antarcticus spawns midwater; its fecundity is 10–25 thousand eggs. Egg size is 3.2–3.3 mm. In M. ingens spawning takes place in the austral autumn and winter, in G. antarcticus—in austral winter. Our data and the literature data show that the so-called “synchronous ovulation” probably occurs in all deepwater squids. This pattern is very rare among fish, but is quite common among benthic octopods that brood their egg masses.     

Age-related shifts in the diet composition of southern elephant seals expand overall foraging niche

Southern elephant seals are important apex predators in a highly variable and unpredictable marine environment. In the presence of resource limitation, foraging behaviours evolve to reduce intra-specific competition increasing a species’ overall probability of successful foraging. We examined the diet of 141 (aged 1–3 years) juvenile southern elephant seals to test the hypotheses that differences between ages, sexes and seasons in diet structure occur. We described prey species composition for common squid and fish species and the mean size of cephalopod prey items for these age groups. Three cephalopod species dominated the stomach samples, Alluroteuthis antarcticus, Histioteuthis eltaninae and Slosarczykovia circumantarcticus. We found age-related differences in both species composition and size of larger prey species that probably relate to ontogenetic changes in diving ability and haul-out behaviour and prey availability. These changes in foraging behaviour and diet are hypothesised to reduce intra-specific food competition concomitant with the increase in foraging niche of growing juveniles.     

The trophic ecology of two abundant mesopredators in south-east coastal waters of Tasmania, Australia

Investigating predator–prey relationships is an important component for identifying and understanding the factors that influence the structure and function of ecosystems. Mesopredators, defined as mid-level predators, have a profound effect on ecosystem structure by contributing an important link between apex predators and lower trophic levels. The diet of two elasmobranch mesopredators, Squalus acanthias and Mustelus antarcticus, was investigated in three locations in south-east Tasmania. Squalus acanthias consumed predominantly pelagic teleosts and cephalopods, while M. antarcticus predominantly consumed benthic crustaceans. As a result, there was low dietary and niche overlap between the two species. There was however evidence of intra-specific dietary variations between locations for both the species. This study has contributed to a better understanding of the top-down dynamics of the food web in coastal Tasmania, by providing important dietary information of two abundant mesopredators. In addition, the similar dietary patterns for S. acanthias and other Mustelus species over much of their global range suggest they may be consistent in their trophic roles across systems, with limited competition between these two sympatric mesopredators to be expected.     

On living in cold water: K-strategies in antarctic benthos

Comparison of the life-histories of two species pairs of caridean decapods, each pair containing a polar and a more temperate-water species (Chorismus antarcticus (Pfeffer, 1887)/Pandalus montagui Leach, 1814 and Notocrangon antarcticus (Pfeffer, 1887)/ crangon crangon (Linnaeus, 1758), suggested that in each case the polar species was more of a K-strategist than was the temperate species. In particular there were striking differences in brood size, egg weight and maturity of the newly hatched larvae. Measurements of individual annual reproductive effort, RE, as g fresh weight eggs per g fresh weight female indicated that in both species pairs the RE of the polar K-strategist was significantly less than that of the comparable temperate water r-strategist. Results expressing RE as g total egg lipid per g fresh weight female were equivocal. These data are discussed in relation to available autecological information for Anterctic marine invertebrates and it is concluded that many features of the polar benthos are explicable in terms of a general evolution of typical K-strategies. The role of low temperature in the widespread evolution of K-strategies may be crucial; consideration of this leads to a re-appraisal of cold-adaptation.     

Investigation of the relationship between invertebrate predation and biochemical composition,energy content,spicule armament and toxicity of benthic sponges at McMurdo Sound,Antarctica

The biochemical and energetic composition, spicule content, and toxicity of benthic sponges was investigated in McMurdo Sound, Antarctica from October through December 1984. The predominant organic constituent of sponges was soluble and insoluble protein. Levels of total protein ranged from 17.0 to 55.9% dr. wt. Levels of lipid and carbohydrate were low, ranging from 2.1 to 9.6 and 0.6 to 3.5% dr. wt, respectively. Levels of ash were high and variable (32 t0 79% dr. wt), reflecting species-specific differences in spicule contents. Calculated energy contents of sponges were low, with a mean of 9.8±3.5 kJ g^-1 dr. wt; ranging from 5.1 kJ g^-1 dr. wt in Sphaerotylus antarcticus to 17.4 kJ g^-1 dr. wt in Dendrilla membranosa. Insoluble protein accounted for the greatest contribution to the energetic composition of the sponges, while lipid and carbohydrate combined contributed to less than 25% of the overall energy. Normalized spicule volumes of sponges ranged from 0.15 to 0.38 cm³ g^-1 dr. wt. Ichthyotoxicity assays indicated that 9 (56%) of 16 antarctic sponge species were toxic. The most highly toxic species were Mycale acerata and Leucetta leptorhapsis. The high incidence of toxicity in antarctic sponges indicates that the current hypothesis suggesting a simple inverse relationship between toxicity and latitude in marine sponges is invalid. There was little correspondence between the energetic composition or spicule contents of the sponges and feeding patterns (electivity indices) of sponge-eating predators. Although the asteroid Perknaster fuscus antarcticus specializes on the highly toxic, fast-growing M. acerata, most antarctic sponge-eating predators appear to be generalists which feed on the more abundant, non- to mildly-toxic, sponge species. This feeding strategy is based on exploitation of low energy, sedentary prey, which require a minimal energy output to harvest.     

Age determination in the Antarctic shrimp Notocrangon antarcticus (Crustacea: Decapoda), using the autofluorescent pigment lipofuscin

Determination of basic population parameters in long-lived Crustacea is hindered by a lack of appropriate methods for age determination. This study uses the pigment lipofuscin as an age marker in the common Antarctic decapod Notocrangon antarcticus (Pfeffer, 1887) from the eastern Weddell Sea. Resin brain sections of the lateral somacluster of the olfactory lobe of 189 specimens were digitally recorded by confocal microscopy and images were subsequently analyzed. A modal progression analysis of the lipofuscin concentration–frequency distribution revealed a total of eight regularly spaced modes presumed to reflect consecutive annual age classes. All eight modes contained females, and the first four contained males. No regular modes were obvious in the comparable length-frequency distribution. The average yearly pigment accumulation was nearly linear and estimated as 0.02% area fraction year⁻¹, which is considerably lower than rates published for species from lower latitudes. This is probably explained by the effect of low water temperature on metabolism and lipofuscin accumulation rate. The growth parameters CL_∞ and k from the von Bertalanffy growth function were 22.3 mm and 0.79 year⁻¹ for females, respectively, and 16.9 mm and 0.64 year⁻¹ for males, respectively. Mortality, estimated from catch curves, amounted to 0.44 year⁻¹ in females and 0.92 year⁻¹ in males, whereas P/B, calculated from the mass specific growth rate method, was slightly lower. The results indicate that the lipofuscin-inferred population parameters are an improvement over what can be learned about N. antarcticus with traditional methods. Received: 1 August 2000 / Accepted: 21 September 2000     

Cephalopod remains from the stomach of a sperm whale stranded off Patagonia

The stomach of a male sperm whale (Physeter macrocephalus) stranded near Comodoro Rivadavia, Argentina, on 21 March 1986, contained 247 cephalopod beaks (128 upper and 119 lower). The lower beaks were identified, their rostral lengths were measured and used to estimate the mantle lengths and wet weight of the representatives of each cephalopod taxon. Fifteen species from nine families were represented. The most numerous species, in order of decreasing abundance, were the large cranchiidMesonychoteuthis hamiltoni (32.8% of total numbers),Mastigoteuthis sp. A (16.0%), andKondakovia longimana andHistioteuthis atlantica (both 13.5%). Almost 85% of the estimated total weight was contributed by two species,Mesonychoteuthis hamiltoni (61.6%) andK. longimana (23.1%). The presence of beaks fromK. longimana, Alluroteuthis antarcticus andM. hamiltoni, which are all thought to be restricted to the Antarctic, suggests that the whale had migrated North prior to stranding.     

Fatty acid signatures of stomach contents reflect inter- and intra-annual changes in diet of a small pelagic seabird,the Thin-billed prion <Emphasis Type="Italic">Pachyptila belcheri</Emphasis>

In diet analyses of seabirds, fatty acid signatures (FAS) can be used to overcome biases due to differential digestion of prey and enable the analysis of very digested diet samples. We applied FAS analysis to stomach contents of a small sub-Antarctic seabird, the Thin-billed Prion Pachyptila belcheri, which feeds mainly on squid during incubation and on crustacea during chick rearing. This seasonal dietary switch of Thin-billed prions was reflected in differences in FAS in regurgitates, as were inter-annual differences in diet composition. A discriminant function analysis correctly classified 93.4% of cases with respect to year (2006–2008) and stage of the breeding cycle (incubation versus chick rearing). The dominant types of crustacea in the diet of Thin-billed prions (amphipods Themisto gaudichaudii, euphausiids, decapods Munida gregaria, and calanoid copepods) were distinguished well by characteristic FAS patterns. However, the FAS of the two main types of prey by volume, amphipods T. gaudichaudii and squid Gonatus antarcticus, were similar to each other. Although FAS were successfully applied in the analysis of prey in stomach contents of prions, FAS of some prey species were similar and may not be distinguishable from each other if used in quantitative diet analyses.     

Feeding ecology of Spinocalanus antarcticus, a mesopelagic copepod with a looped gut

Spinocalanus antarcticus, an abundant mesopelagic copepod in polar seas, has a greatly elongated and looped midgut, contrary to most other copepod species. The total gut length is 1.77, 1.86 and 1.90 times the total body length in adult females, CV and CIV, respectively. Gross morphology of the midgut is similar in all copepodite stages and adults. It is described here from specimens collected in the Arctic Ocean. In stratified samples from the deep Amundsen and Makarov Basins S. antarcticus showed a clear preference for the depth layer between 100 and 500 m. Generally, the guts were packed with material, but most of it was impossible to identify. In most specimens the digestive tract was filled with undefined detritus particles ("detritus balls"). They were almost spherical, heterogeneous organic aggregates of 40-100 µm diameter, with small clay-sized mineral flakes imbedded. Mineral particles in the size range of 1-10 µm were found in large quantities in the guts of many specimens. Cysts of Chrysophycea and dinoflagellates and fragments of dinoflagellates, diatoms, tintinnids and radiolarians, as well as skeletons of silicoflagellates, were rather rare; some animal remnants were also found. A high carbon/nitrogen ratio (8.9) and very high lipid content (54% of dry weight) indicated a very good nutritional state. The adaptive significance and possible feeding strategy of this deep-water copepod is discussed.     

Shearwater diet during migration along the coast of Rio Grande do Sul,Brazil

The coastline of the state of Rio Grande do Sul (Brazil) is used annually as a migratory route by a number of seabird species. Thirteen surveys were carried out between July 1997 and July 1998 to obtain information on the diet of Puffinus gravis, Puffinus griseus, and Puffinus puffinus along the coast of Rio Grande do Sul. Sampling efforts focused on dead beach-cast specimens. One hundred twenty-one stomach content analyses were performed on P. gravis from a total of 238 specimens; 17 stomach content analyses were performed on P. griseus from a total of 54 specimens; and 25 stomach content analyses were performed on 25 P. puffinus from a total of 61 dead specimens. Cephalopods were the main prey found in the stomachs of the three species and were present in 96% of the P. gravis stomachs. The following cephalopods were observed: Ommastrephidae, Gonatus antarcticus, Gonatus sp., Lycoteuthis lorigera, Lycoteuthis sp., Histioteuthis sp., Cycloteuthis sp., Loligo plei, Loligo sanpaulensis, Sepiidae, and Argonauta nodosa. The latter was the most abundant species in the three species of Puffinus. The following fish were identified from otoliths: Porichthys porosissimus, Ctenosciaena gracilicirrhus, Paralonchurus brasiliensis, Cynoscion guatucupa, and Trichiurus lepturus. There was also a high incidence of synthetic materials such as plastic, polyethylene and rubber.     

Growth,food utilization and effect of social interaction in the European bass Dicentrarchus labrax

Fingerling and juvenile bass, Dicentrarchus labrax (L.) fed on filleted saithe, Gadus virens, exhibited much higher K ₁ energy and nitrogen utilization efficiencies (growth as % energy or nitrogen intake) than those fed on trout pellets or shore crabs, Carcinus maenas, although the efficiency declined during prolonged feeding. Mean organic absorption efficiency for saithe was 99.5% and was independent of food intake but the efficiency for pellets and crab declined with increasing food intake from 99 to 92%. For each diet the regression of relative growth rate on food intake was linear up to the regression of relative growth rate on food intake was linear up to the highest feeding level and independent of body weight, enabling construction of a simple model for food transformation. The regression coefficient (equivalent to K ₃, the ratio of growth to food consumed in excess of maintenance) for saithe was about 3 times that for pellets in terms of energy and twice that for pellets in terms of nitrogen. The more efficient utilization of saithe for growth and of pellets for maintenance were related to differences in their nutritional value. With each diet, K ₃ and maximum K ₁ for energy were about twice those for nitrogen. Social interaction had a significant effect on food utilization in juvenile bass. Isolated fish showed poor growth and mean K ₁ efficiency in comparison with bass in pairs or groups. K ₃ efficiency and mainternance requirement were similar in individuals and groups, but were significantly greater in pairs. These results are related to behavioural observeations and environmental stress, and the limitations of extrapolating the results of laboratory feeding experiments on fish to other situations is discussed.     

Food selectivity of the rotifer Brachionus plicatilis feeding on phytoplankton

Food selectivity was examined in amictic female rotifers, Brachionus plicatilis, fed Chlamydomonas sp. and Olisthodiscus sp. Filtering and ingestion rates of the rotifers in a single food suspension were higher with Chlamydomonas sp. than with Olisthodiscus sp. In every mixture of two food species, the apparent filtering rate on Chlamydomonas sp. was much higher than that on Olisthodiscus sp. Total filtering rate and apparent filtering rate in food suspensions containing Chlamydomonas sp. decreased with increasing cell concentration of Chlamydomonas sp. Total and apparent filtering rates were calculated from the decrease in total food concentration as well as from decreases in concentrations of each of the two food algae, respectively. B. plicatilis ingested Olisthodiscus sp. at an extremely low constant rate in all mixtures. The degree of food selectivity of the rotifers fed Chlamydomonas sp. (i.e., selective filtration) from the mixture of two food algae decreased with increasing cell concentration of Chlamydomonas sp. Filtering and ingestion rates of rotifers fed senescent Chlamydomonas sp. were relatively lower than those fed Chlamydomonas sp. in the exponential phase. This indicates that Brachionus plicatilis displays selectivity in regard to condition of cells as well as type of food.     

Trophic relationships of white-chinned petrels from Crozet Islands: combined stomach oil and conventional dietary analyses

The diet of white-chinned petrels Procellaria aequinoctialis breeding at the Crozet Archipelago (southern Indian Ocean) was studied using two complementary methods: lipid analysis of stomach oils as trophic markers together with the conventional dietary approach (i.e., stomach content analysis). Objectives were (1) to investigate the adult diet when they feed for themselves by analyzing stomach oil lipids, and (2) to compare the lipid signature of chick and adult oils. Stomach oils mainly consisted of triacylglycerols (TAG), diacylglycerol-ethers (DAGE) and wax esters (WE) (66, 14 and 11%, respectively). The dietary origin of TAG and WE was evaluated by linear discriminant analyses with fatty acid and fatty alcohol fractions. Analyses evidenced that stomach oils did not originate from Antarctic krill, but instead from myctophid fish, thus demonstrating the importance of mesopelagic fish in the nutrition of adult petrels. This result was consistent with the identification of digested remains of myctophids recovered from adult stomach contents after long foraging trips. Large amounts of a rare lipid class, DAGE (up to 76% of total lipids), were identified in two stomach oils, together with fresh remains of the squid Gonatus antarcticus (99% by mass), suggesting that DAGE could have the potential to be trophic markers of cephalopods. Moreover, six oils probably originated from Patagonian toothfish, thus confirming strong interactions between white-chinned petrels and fisheries. Comparison between chick and adult stomach oils indicated no major differences in their biochemical composition suggesting an identical dietary origin of oils, mainly myctophids. Both adult and chick oils can therefore be used to determine the feeding ecology of adult birds when they feed far away from their breeding grounds. Finally, food analysis of chick samples and adult samples collected after short and long trips indicated different foraging grounds during the two kinds of trips, and also between long trips performed in subtropical and Antarctic waters.     

Effect of food location and quality on recruitment sounds and success in two stingless bees,<Emphasis Type="Italic"> Melipona mandacaia</Emphasis> and<Emphasis Type="Italic"> Melipona bicolor</Emphasis>

It is unclear whether stingless bees in the genus Melipona (Hymenoptera, Apidae, Meliponini) can reliably encode the distance to a food source through recruitment sounds produced inside the nest, in part because the sound features correlated with distance also vary with food quality. We therefore trained marked foragers of two species, Melipona mandacaia and M. bicolor, to feeders at different distances and to different sucrose concentrations at the same distance. In both species, foragers successfully recruited to a rich 2.5-m food source and produced pulsed recruitment sounds in which pulse duration was significantly and positively correlated with distance to the rich food source. When returning from poorer food sources (0.6–1.5 m), foragers of both species decreased sound production, producing shorter sound pulses and longer sound interpulses than they did for 2.5 m food located at the same distance. Thus the temporal structure of M. mandacaia and M. bicolor recruitment sounds varies with distance and food quality. However, nestmates were not recruited by performances for poorer food sources (0.6–1.5 m), whose sucrose concentration was sufficiently low to affect recruitment sounds. Surprisingly, the interphase (the time between behavioral phases that communicate location) also increases with decreasing food quality in the closely related honeybees (Apis), suggesting a potential homology in the effect of food quality on the recruitment systems of Apis and Melipona. We explore the evolutionary implications of these similarities.Communicated by M. Giurfa     

Dietary-induced responses in the phagotrophic flagellate Oxyrrhis marina

Primary producers may be limited by different nutrients as well as by light availability, which in turn affects their quality as food for higher trophic levels. Typically, algae with high C:N and/or C:P ratios are low-quality food for consumers. Heterotrophic protists are important grazers on these autotrophes, but despite their importance as grazers, knowledge of food quality effects on heterotrophic protists is sparse. In the present study, we examined how differently grown Rhodomonas salina (nutrient replete, N-limited and P-limited) affected the phagotrophic flagellate Oxyrrhis marina. The functional response of O. marina (based on ingested biovolume) did not show significant differences between food sources, thus food uptake was independent of food quality. O. marina was weakly homoeostatic which means that its C:N:P ratio still reflected the elemental composition of its food to some extent. Food quality had a significantly negative effect on the numerical response of O. marina. Whereas N-limited R. salina and nutrient replete R. salina resulted in similar growth rates, P-limited algae had a significantly negative effect on the specific growth rate of O. marina. Hence, the lack of elemental phosphorus of O. marina feeding on P-limited algae caused a reduction in growth. Thus, despite their weaker homoeostasis, heterotrophic protists are also affected by high C:P food in a similar way to crustacean zooplankton.     

Feeding habits and food requirements of some amphipods in the Black Sea

Food composition and food requirements of four amphipod species of the Black Sea — Dexamine spinosa (Mont.), Amphithoe vaillanti Lucas, Gammarellus carinatus (Rathke), Gammarus locusta L. — were studied and an attempt made to assess the quantitative composition of the food, daily rhythms of feeding, and daily food rations. The composition of the food of the above-named amphipods is similar and consists primarily of seaweeds. Daily feeding intensity is characterized by a distinct increase during the dark period (D. spinosa, A. vaillanti); however, in G. locusta feeding intensity increases in the morning. The daily food rations of amphipods vary greatly (from 1.7 to 360% of the specimens' body weight), depending upon factors such as the kind of food, age, sex, the physiology of specimens, and the water temperature. The total quantity of food eaten by the populations of these amphipods in the coastal zone of the Black Sea amounts to 4000 g organic matter per square metre within 1 year.