Copepod Diet Research Articles

The lipid, fatty acid and fatty alcohol composition of the myctophid fish Electrona antarctica: high level of wax esters and food-chain implications

The myctophid, Electrona antarctica, was collected by trawl from the Elephant Island region of the Antarctic Peninsula, and from East Antarctica near 61°S and 93°W. Total lipid was higher in Elephant Island E. antarctica (whole fish, 466–585 mg g−1 dry weight) than those from Eastern Antarctica (394–459 mg g−1). Wax esters comprised 86.2–90.5% of total lipid in E. antarctica flesh. There were no significant differences between Eastern Antarctica and Elephant Island in total wax ester levels, or in levels of wax esters between different tissues analysed. Oily bones (up to 326 mg g−1 in the neurocranium) characterized E. antarctica from both locations, with wax esters as the major skeletal lipid class (67.0–87.9%, percent of lipid). The wax esters may have a buoyancy role in E. antarctica. The only substantial amount of triacylglycerols (29.4%) were found in the viscera of Elephant Island fish. The principal fatty acids of all fish analysed included the monounsaturated fatty acids 18:1(n-9) and 16:1(n-7), with lower levels of 16:0 and 14:0 saturated acids. Fatty alcohols were dominated by the saturated 16:0 and 14:0 (37.8–47.8%) and the monounsaturated 18:1(n-9) and 18:1(n-7) (38.3–59.2%). The low ratio of 22:1/20:1 alcohols observed for E. antarctica is consistent with a diet of amphipods, copepods and other items low in 22:1 alcohols.

Flux of particulate matter through copepods in the Northeast water polynya

Particulate organic carbon (POC) and nitrogen (PON) production by large calanoid copepods was investigated on the northeast Greenland shelf during August 1992 and May to August 1993. Both Calanus hyperboreus and C. glacialis females, when suspended in seawater collected from the chlorophyll maximum, produced about 40 pellets per day, which contained a carbon and nitrogen content equivalent to 8% and 6% of body carbon, respectively, and 2% of body nitrogen. In experiments, the carbon:nitrogen (C:N) ratio by weight of suspended particulates, C. hyperboreus, and fecal pellets was 6.7, 7.7 and 28.5, respectively. The unusually high C:N ratio for pellets, in part, may be attributed to elevated ratios of > 20μm size fractions of particulate organic matter, the size fraction more common in the diet of these large copepods and the fraction dominated by diatoms according to microscopic and pigment data. The implied elevated C:N ratios of large phytoplankton cells were probably due to nitrogen deficiency, as shown by other studies in this region. In addition, female C. hyperboreus appeared to be more efficient in assimilating nitrogen than carbon, which also would have contributed to high C:N ratios in egested pellets. Unfractionated POC concentrations explained 54% of the variability in carbon egestion and 70% of the variability in nitrogen egestion in copepods, whereas copepod body content accounted for little of the variation on the short time scales of the experiments. Carbon egestion by C. hyperboreus was positively correlated with POC concentrations at the depth of the chlorophyll maximum, while nitrogen egestion was negatively correlated with PON concentrations in the euphotic zone. Estimates of potential community egestion rates for the upper water column indicate that copepods represent a major pathway of organic carbon transformation in this Arctic shelf system. On average, copepods may have ingested 45% of the primary production and egested fecal matter equivalent to 20% of the carbon and 12% of the nitrogen particulate flux sedimenting from the surface layer. However, several lines of evidence suggest that pellets were remineralized in the water column and, hence, may have contributed little organic carbon and nitrogen to the benthos.

Diets of calanoid copepods on the West Florida continental shelf: Relationships between food concentration, food composition and feeding activity

Bottle incubations were conducted in March, July/August and October 1992. to measure the daily rations (R) and objectively characterize the diets of the calanoid copepodsEucalanus elongatus, Undinula vulgaris, Centropages velificatus andTemora stylifera from the west Florida continental shelf. Daily rations,R, were clustered around two, order-of-magnitude different means, 1.3 and 11.2% of body C d−1, representative of quiescent and active feeding modes, respectively. The food concentration at which the transition from quiescent to active mode occurred was influenced by food particle size. In the quiescent mode, diets were dominated by nanoplankton, whereas no food type dominated the diet in the active mode. Selective feeding, defined as a statistically significant difference between the frequency distributions of foods in the diet and environment, occurred in both quiescent and active copepods. However, what appeared to be selective feeding in quiescent copepods could be explained by processes that passively modified the distribution of the diet relative to that of the food supply. Conversely, selective feeding in active copepods apparently resulted from foraging for particles >5 μm in diameter in food environments dominated by nanoplankton (<5 μm).

The diatom Thalassiosira rotula affects reproductive success in the copepod Acartia clausi

Fecundity, egg viability and fecal pellet production are reported for Acartia clausi females collected in the Bay of Naples, Italy, from April to October 1992 and fed either with a diatom (Thalassiosira rotula) or dinoflagellate (Prorocentrum minimum) diet, at food saturated conditions. The diatom diet significantly reduced both egg and fecal pellet production as well as hatching success. Blockage of egg development occurred with both axenic and non-axenic cultures of T. rotula, suggesting that inhibitors were provided by the diatoms and not by the bacteria associated with diatom cultures. Low hatching success was also artificially induced by exposing newly spawned A. clausi eggs to high concentrations of diatom extracts, indicating the presence of deleterious, inhibitory compounds blocking copepod embryogenesis. Fecundity and hatching success diminished significantly with female age. In contrast, female longevity was not significantly modified by food type. The presence of males did not significantly alter fecundity or egg viability. Females continued to produce viable eggs throughout the period of incubation, with and without males, in both food conditions, indicating that remating is infrequent and not necessary to sustain viable egg production in this species. The succession in low and high population densities may therefore be the outcome of variations in survival rates of eggs, rather than reproductive protential perse; such variations may strongly depend on the adult copepod diet.

Ontogeny of copepod predation in juvenile squid (Loligo opalescens).

Copepods are the major prey of juvenile squid, and small species of squid such as Loligo opalescens face a great challenge in catching these erratically moving crustaceans. We studied the ontogeny of copepod predation in laboratory-reared animals and found that mastery of copepod capture develops progressively, starting shortly after hatch with strong attacks of a simple type. Modifications of the initial basic attack lead to more specialized strategies that effectively extend the range of capture to both longer and shorter distances. This progression culminates, by approximately 40 days post-hatching, in adult-like prey capture behavior involving tentacle extension and retraction. Squid raised exclusively on easily captured Artemia nauplii and introduced to a copepod diet 40 days after hatching displayed only basic attack behavior, characteristic of very young squid. All of these attacks were unsuccessful, and very few of these animals survived the transition. Copepod capture thus appears to be a skill that must be acquired in an experience-dependent manner early in post-hatching life.

Omnivory and feeding selectivity in five copepod species during spring in the Bellingshausen Sea, Antarctica

Copepod grazing experiments were undertaken along a transect of five stations in the Bellingshausen Sea during austral spring. The stations spanned unproductive, nanoflagellate-dominated waters under pack ice to an open water bloom of large diatoms in the north. The feeding habits of five dominant species were compared by incubating them in natural sea water. Feeding rates on individual food taxa were calculated from optical cell counts. The larger species (Rhincalanus gigas, Calanus propinquus, and Calanoides acutus) tended to eat larger cells than did Oithona spp. and Metridia gerlachei, and cleared cells up to 100-200 $[$mu$]$m in length with increasing efficiency. Their clearance of longer cells remained high. Oithona spp. was the only species with high clearance rates on cells smaller than 10 $[$mu$]$m. Clearance rates on elongated cells were compared with those of shorter and fatter cells of similar volume. The longer cells were eaten at higher rates in 65% of comparisons, suggesting that cell elongation did not protect against ingestion by large copepods. Clearance rates of motile cells were compared with those of non-motile diatoms of similar size and shape. The copepods ranged widely, with Oithona spp. at one extreme, ingesting motile cells almost exclusively. M. gerlachei and C. propinquus showed a preference for motile taxa compared with similar sized diatoms. The fact that the motile fraction comprised an array of taxa (nanoflagellates, dinoflagellates, and ciliates), all with a tendency to be cleared more rapidly than diatoms by the above three species, suggests that they were using mechanoreception to detect prey. Oithona spp., M. gerlachei, and C. propinquus were actively feeding under the ice before the bloom, in low productivity waters characterized by a nanoflagellate community and a high inorganic detritus content. The selection for motile taxa persisted, by M. gerlachei at least, into the bloom, even though motile cells comprised only a small fraction of available carbon at that tim C. acutus and R. gigas by contrast, migrated to the surface layers to start feeding on the bloom. These two species appeared to have fed indiscriminately on both motile and non-motile taxa. The contribution of motile taxa to copepod diets depended on their contribution to the overall food source, the extent of motile/sessile selection, and also on their size and shape relative to the diatoms. Consequently the proportion of motile taxa in copepod diets ranged from 100% (Oithona spp. before the bloom) to 3% (R. gigas during the bloom).

Diet of copepods (Scopalatum vorax) associated with mesopelagic detritus (giant larvacean houses) in Monterey Bay, California

The feeding structures or “houses” of the giant larvacean Bathochordaeus sp. serve as both habitat and food for the calanoid copepod Scopalatum vorax. Gut contents of S. vorax include both microbial and metazoan associates of larvacean houses, and possibly the house-mucus matrix itself. Copepods were observed and collected from larvacean houses between 100 and 500 m in Monterey Bay, California, using a submersible ROV (remotely operated vehicle) from the Monterey Bay Aquarium Research Institute. Gut contents were compared to potential food items on the houses and in the open water (not associated with the house). Copepods were generalist feeders, with amorphous detritus, diatoms, and copepods or other crustacean parts dominating gut contents. Protozoans and algae other than diatoms were rarer in guts. Houses contained a diverse assemblage of microplankton and metazoans, both intact specimens and detrital remains of these. Numbers of diatoms and fecal pellets were enriched by 1 to 3 orders of magnitude on houses compared to numbers in surrounding water. Many of the abundant species of diatoms and copepods on houses occurred in S. vorax guts. This observation coupled with S. vorax feeding habits observed in situ and in the laboratory provide evidence for feeding on houses. S. vorax appears to possess special adaptations to living in a resource-limited environment, such as gorging as a feeding adaptation, chemosensory structures to help locate houses, and the ability to change feeding modes. Consumption of detritus at depth by S. vorax provides evidence that metazoans contribute to remineralization of particulate organic carbon in the mesopelagic zone.

Regulation of zooplankton biomass and production in a temperate, coastal ecosystem. 2. Ciliates

Seasonal distributions of biomass, egg production, and production rates of the pelagic copepod community were compared to the variation in abundance and size and taxonomic composition of the microplankton in the southern Kattegat, Denmark. Copepod production was episodic and occurred in bursts associated with three net phytoplankton blooms. The seasonal distribution of copepod biomass, on the other hand, was unimodal with peak concentrations in June-July. The vernal increase in copepod biomass coincided with the spring production burst, but copepod biomass was otherwise unrelated to the seasonal variation in copepod production. Specifically, the continuous decline in copepod biomass between early August and late October overlapped the most significant production event during the year (August-September) and must, therefore, have been caused by elevated mortality during this period. Weight-specific egg production rates in several species of copepods were similar and varied in concert. Egg production rates varied significantly with the concentrations of chlorophyll (> 11 pm) and total microplankton biomass but were unrelated or only weakly related to other components of the microplankton (dinoflagellates, nanoflagellates, ciliates, and copepod nauplii). Significant egg production occurred only when concentrations of diatoms and other large phytoplankters were high and ciliates were too dilute to contribute significantly to copepod diet during these production bursts. However, microzooplankton concentrations were sufficient to account for observed egg production rates when these were low during major parts of the year. Although microzooplankton may ensure a nutritionally complete diet throughout the year, integrated annual copepod production appears to depend primarily on episodic net phytoplankton blooms.

Regulation of zooplankton biomass and production in a temperate, coastal ecosystem. 1. Copepods

Seasonal distributions of biomass, egg production, and production rates of the pelagic copepod community were compared to the variation in abundance and size and taxonomic composition of the microplankton in the southern Kattegat, Denmark. Copepod production was episodic and occurred in bursts associated with three net phytoplankton blooms. The seasonal distribution of copepod biomass, on the other hand, was unimodal with peak concentrations in June–July. The vernal increase in copepod biomass coincided with the spring production burst, but copepod biomass was otherwise unrelated to the seasonal variation in copepod production. Specifically, the continuous decline in copepod biomass between early August and late October overlapped the most significant production event during the year (August–September) and must, therefore, have been caused by elevated mortality during this period. Weight-specific egg production rates in several species of copepods were similar and varied in concert. Egg production rates varied significantly with the concentrations of chlorophyll (>11 µm) and total microplankton biomass but were unrelated or only weakly related to other components of the microplankton (dinoflagellates, nanoflagellates, ciliates, and copepod nauplii). Significant egg production occurred only when concentrations of diatoms and other large phytoplankters were high and ciliates were too dilute to contribute significantly to copepod diet during these production bursts. However, microzooplankton concentrations were sufficient to account for observed egg production rates when these were low during major parts of the year. Although microzooplankton may ensure a nutritionally complete diet throughout the year, integrated annual copepod production appears to depend primarily on episodic net phytoplankton blooms.

Influence of ontogenetic changes in prey selection on the survival and growth of rohu, Labeo rohita and singhi, Heteropneustes fossilis larvae

When offered a mixed diet of different zooplanktonic items covering a body size range of 75–2200 μm, (a) rohu, Labeo rohita and (b) singhi, Heteropneustes fossilis larvae ingested progressively larger prey as they grew, due to age‐related increase in gape. However, a nearly constant prey size/mouth size ratio was maintained for a period of 4wk after hatching. The dominance of rotifers in the diet during the first 2‐wk was followed by cladocerans, particularly Moina macrocopa. Significant differences observed in the growth rates of the larvae reared on different diet regimes were related to ontogenetic changes in prey selection. An exclusive copepod diet throughout resulted in the lowest weight gain in the larvae of both species. However, copepods had no apparent adverse effects when present with the preferred rotifers and cladocerans. Although constituting a suboptimal prey size for the older larvae, rotifers alone, when present in sufficient densities, produced growth rates comparable to those obtained on a cladoceran diet. However, a mixed diet regime contributed to the maximum growth. The implications of these findings to rearing larvae of the economically important rohu and singhi are discussed.

Nutritional Factors Affecting Stress Resistance in the Larval Mahimahi Coryphaena hippurus

AbstractRecent improvements in enriching Artemia make mahimahi culture possible without using copepods. Mahimahi survive better when cultured copepods Euterpina acutifrons are used, especially when the larvae are under stresses such as high stocking density, cold weather, or the rigors of metamorphosis. This study looked at some differences between copepods and enriched Artemia.This study tested stress resistance by holding postlarval (PL) mahimahi out of water in a hand net for varying periods of time. Recovery from this stress shock was higher in PLs whose diet was higher in docosahexaenoic acid (DHA). DHA appeared to play an important role in stress resistance. High eicosapentaenoate (EPA) or high HUFA did not confer stress resistance when DHA levels were low. Copepods contained higher levels of many essential amino acids in addition to higher levels of DHA compared with enriched brine shrimp.Larvae sickened by disease appeared to lose fat, including DHA, but they conserved DHA relative to other fatty acids. Even when sick, mahimahi larvae fed a copepod diet resisted stress better than larvae fed an enriched brine shrimp diet.Optimal Artemia enrichment levels of DHA for mahimahi have not been reached and this may explain why it has been difficult for others to raise this fish consistently. E. acutifrons is relatively easy to culture, but may not be practical for commercial hatcheries, due to low yield (less than 10 g per 100 L per week).

On the diets of calanoid copepods

A review of the literature (ca 1900 to 1992) on copepod feeding indicates that combinations of stochashc and deterministic processes result in behaviors, or feeding strategies, that optirnize nutritional gain from the food environment, and further, that strategies change in response to environmental variability. Because the diet is the product of a feeding strategy, one may gain insight into the ways in which copepods respond to their food environments by measuring their diets. Investigations of the hnks between copepod feeding and production suggest that dietary diversity is often a key to the procurement of a nutritionally complete ration, and the optimization of secondary production within constraints dictated by the physical environment. The ability to eat different kinds of foods (ornnivory) and the tendency to include a variety of foods in the daily ration may enhance the probabhty of obtaining a nutritionally complete ration in variable, nutritionally dilute, food environments. The notion that the relationshp between feeding and production in copepods is driven by clletary diversity is derived in part from a recent recognition of the diversity of microplanktonic organisms that potentially or actually contribute to the diet. Further, the concept is consistent with current trophic dynamic models in which food webs are envisioned as complex interwoven systems rather than short, simple chains.

Trophic interactions between copepods and microplankton: A question about the role of diatoms

Relationships among microplankton composition, copepod diet, and egg production are examined with data from gut content analysis of copepods from California coastal waters and from the Irish Sea, feeding and egg production experiments on Acartia tonsa off southern California, and egg production measurements on copepods from a subtropical estuary (Port Everglades, Florida), temperate shelf waters (southern California, Irish Sea), and the open ocean (Gulf Stream). The copepod species studied appeared to feed preferentially on dinoflagellates and microzooplankton relative to diatoms. Patterns of variability in egg production conform, generally, to changes in dinoflagellate and microzooplankton biomass, but seem to be independent of changes in diatom biomass.

Effects of a storm event on the structure of the pelagic food web with special emphasis on planktonic ciliates

Storm-induced changes in the water column structure and the pelagic food web were investigated by daily sampling during a 3 week period (October 24 to November 10, 1988) at a permanent station in the southern Kattegat (Denmark) Subsequent to a storm the primary production increased and the size-distribution of the phytoplankton changed towards larger cells. Some components of the zooplankton community responded to the increase in potential food, either in terms of a functional response (copepods) or in terms of a numerical response (cladocera), whereas no changes in the populations of mixo- and heterotrophic aliates were evident. The dilates were not food limited since growth rates determined in situ were comparable to maximum growth rates measured in the laboratory. Calculations suggest that the total clearance capacity of planktonic copepods (as fraction of water column cleared per unit time) was of the same magnitude as the measured instantaneous growth rates of the ciliates (0.55–0 85 day −1 ). Ciliate populations were therefore probably limited by copepod predation. Ciliates, however, contributed only insignificantly to the diets of copepods. Although the total zooplankton production increased by at least 30% subsequent to the storm (and that of the copepods by 50%), the zooplankton community was unable to assimilate the entire increase in primary production. The relative zooplankton (copepods, cladoceran and ciliates) grazing rate on the primary production decreased ∼30%, and the flow of carbon to biomass accumulation, other grazers and in particular sedimentation is predicted to have increased by 100% following the storm.

The food of immature sprat (Sprattus sprattus (L.)) and herring (Clupea harengus L.) in coastal waters of the North Sea

Immature sprat ( Sprattus sprattus (L.)) and herring ( Clupea harengus L.) from the North Sea, caught from June 1981 to April 1982 in the cooling waters of Sizewell nuclear power station, had similar diets of copepods in fish up to 7 cm in length. Larger sprats continued to feed on copepods, but herring took increasingly larger food items as they grew. Mysids and post-larval sprat contributed most to the diet of herring 7–20 cm in length, and feeding continued throughout the year. No food organisms were found in sprats above 9 cm in length from July to February, and all sprats ceased to feed in December and January. Feeding was resumed in February and reached a peak of intensity in June. Immature sprat and herring caught at a series of stations along the length of the east coast of England in July 1984 had diets similar to those of the Sizewell fish.

Kinetic Properties of Digestive Carbohydrases and Proteases of Zooplankton

Copepod carbohydrases and proteases obtained from acetone-dried powder were tested for the effects of various physical–chemical factors. Influences of pH, temperature, substrate concentration, and time of incubation were studied to establish the optimal enzyme assay conditions. Enzyme activities were found that catabolyzed most sugars assayed (amylose, laminarin, cellulose, maltose, cellobiose, lactose, trehalose, α-mannoside, etc.) as well as those catabolyzing most proteins (hemoglobin, albumin, azocoll, cowhide azur). The spectrum of digestive enzymes found is discussed in terms of natural substrate availability. Certain enzymes, such as mannosidase or the chitobiases could be related to the bacterial component in the copepod intestinal flora or diet. From direct and indirect evidences it was possible partially to identify the amylase as an α-amylase, the acid protease as a cathepsin-like enzyme, and one of the alkaline proteases as a trypsin-like enzyme.Key words: kinetic properties, carbohydrases, proteases, zooplankton

The Parasitic Copepod Diet and Life History of Diskfishes (Echeneidae)

Stomach contents from 401 individuals representing six species of echeneids were examined. Parasitic copepods are an important part of the diet of echeneid fishes. Parasitic copepods were present in 70% of the stomachs of Remora remora containing food and in four other species to a lesser, but significant extent. The growth stage of the life history of the echeneid during which it feeds on parasites varies among species. In R. remora the younger individuals are more active as parasite pickers whereas in R. osteochir older specimens are more active. Life history information resulting from extensive collection data is included in the discussion of each of the six species considered.