Grazing by adult estuarine calanoid copepods of the Chesapeake Bay

Grazing by adult female Eurytemora affinis, Acartia tonsa and A. clausi on natural distributions of particles from the Chesapeake Bay has been investigated. During the course of a year's sampling, a wide variety of particle size-biomass distributions were observed as seasonal shifts in detritus, and over 150 algal species occurred. These distributions were grouped into 5 basic types in the analyses of feeding. All three species demonstrated similar capabilities for feeding over a broad range of particle size with selection (higher filtering rates) on larger particles and on biomass peaks. Feeding on multiple-peak distributions resulted in strong selection or tracking of each biomass peak with reduced filtering rates between peaks. Evidence is presented which suggests that the copepods first feed on large particles and then successively switch to biomass peaks of the smaller size categories. Comparisons of the feeding behavior of Eurytemora affinis and the Acartia species showing that the Acartia species have greater capabilities for taking large particles may be associated with modifications of their mouth parts for raptorial feeding. The results suggest considerable flexibility in copepod feeding behavior which cannot be explained solely by the mechanism of a fixed sieve.     

Modification of the feeding behavior of marine copepods by sub-lethal concentrations of water-accommodated fuel oil

The feeding behaviors of Acartia clausi and A. tonsa were measured in samples of water containing low levels of a water-accommodated fraction of No. 2 fuel oil. The copepods fed normally at a hydrocarbon concentration of 70 g l^-1, but their feeding behavior was altered both quantitatively and qualitatively at a concentration of 250 g l^-1. Three types of response to the higher oil level were found. The first was total suppression of feeding. Both other types involved suppression of feeding on particles between 7 and 15 m diameter, but one showed no change in the ingestion of larger particles, whereas the other displayed increased feeding on particles larger than 15 m diameter. These results suggest that the species of Acartia studied use three different modes of feeding, each on a different size range of particulate material. Low-level hydrocarbon pollution affects each feeding mode differently.Contribution No. 973, Center for Environmental and Estuarine Studies of the University of Maryland     

Food size spectra,ingestion and growth of the copepodAcartia tonsa during development: Implications for determination of copepod production

Clearance rates on different sizes of spherically shaped algae were determined in uni-algal experiments for all developmental stages (NII through adult) of the copepodAcartia tonsa, and used to construct food size spectra. Growth and developmental rates were determined at 7 food levels (0 to 1 500 g C l^-1 ofRhodomonas baltica). The lower size limit for particle capture was between 2 and 4 m for all developmental stages. Optimum particle size and upper size limit increased during development from 7 m and 10 to 14 m for NII to NIII to 14 to 70 m and 250 m for adults, respectively. When food size spectra were normalized (percent of maximum clearance in a particular stage versus particle diameter/prosome length) they resembled log-normal distributions with near constant width (variance). Optimum, relative particle sizes corresponded to 2 to 5% of prosome length independent of developmental stage. Since the biomass of particulate matter is approximately constant in equal logarithmic size classes in the sea, food availability may be similar for all developmental stages in the average marine environment. Juvenile specific growth rate was exponential and increased hyperbolically with food concentration. It equaled specific female egg-production rate at all food concentrations. The efficiency by which ingested carbon in excess of maintenance requirements was converted into body carbon was 0.44, very similar to the corresponding efficiency of egg-production in females. On the assumptions that food availability is similar for all developmental stages, and that juvenile and female specific growth/egg-production rates are equal, female egg-production rates are representative of turnover rates (production/biomass) of the entireA. tonsa population and probably in other copepod species as well. Therefore, in situ estimates of female fecundity may be used for a rapid time- and site-specific field estimate of copepod production. This approach is shown to be fairly robust to even large deviations from the assumptions.     

Grazing and ingestion rates of nauplii,copepodids and adults of the marine planktonic copepod Calanus helgolandicus

The average grazing and ingestion rates of all stages of the marine planktonic copepod Calanus helgolandicus (Calanoida) from nauplius stage IV to adults were measured experimentally at 15°C in agitated cultures. The chain-forming diatom Lauderia borealis and the unarmoured dinoflagellate Gymnodinium splendens were offered as food. The food concentrations were close to natural conditions and ranged from 36 to 101 g of organic carbon per liter. The medium body weights expressed in g of organic carbon of almost all larval stages raised at 49 g C/1 were identical with the weight of the same stages caught in the Pacific Ocean off La Jolla, California, USA. In a log-log system, grazing and ingestion rates increased almost linearly with increasing body weight. Grazing rates ranged from 4 to 21 ml/day/nauplius stage IV to 286 ml to 773 ml/day/female. Ingestion rates increased from 0.2 g to 0.8 g C/day/nauplius stage IV to 18 g to 69 g C/day/female. Grazing and ingestion rates per unit body weight decreased gradually with increasing body weight. The daily ingested amount of food decreased from 292 to 481% of the body weight (g C) of nauplius stage V to 28–85% of the body weight of adult females. Grazing and ingestion performances of all stages increased with increasing particle size. Grazing rates decreased and ingestion rates increased with increasing food concentrations. The published data on food intake of the different age groups of C. helgolandicus show that the young stages of herbivorous planktonic copepods can play a major part in the consumption of phytoplankton in the sea due to their high grazing and ingestion rates.     

Zooplankton of the Bristol Channel and Severn Estuary. The distribution of four copepods in relation to salinity

The seasonal variations in distribution and abundance of the common zooplankton species in the Bristol Channel and Severn Estuary were related to the salinity regimes observed over the period November 1973 to February 1975. The dominant constituents in all regions were the calanoid copepods, which reached maximum densities in July: approximately 100 times their winter levels. Four zooplankton assemblages were recognised using an objective classification program which computed similarity coefficients and used group-average sorting. The assemblages existed along the salinity gradient observed from the Severn Estuary to the Celtic Sea. The assemblages were classified as true estuarine, estuarine and marine, euryhaline marine and stenohaline marine and were characterized by the copepods Eurytemora affinis (Poppe) (<30S), Acartia bifilosa var. inermis (rose) (27 to 33.5S), Centropages hamatus (Lilljeborg) (31 to 35S) and Calanus helgolandicus (Claus) (>33S), respectively.     

Accumulation of 14C-1-naphthalene by an oceanic and an estuarine copepod during long-term exposure to low-level concentrations

Accumulation of the bi-cyclic aromatic hydrocarbon ¹⁴C-1-naphthalene in adult female Calanus helgolandicus Claus and adult female Eurytemora affinis Poppe in sea water concentrations of hydrocarbon ranging from 0.2 to 992 g/l was studied during exposure periods of up to 15 days as part of an investigation of the possible effects on marine zooplankton of persistent exposure to low levels of petroleum hydrocarbons. With both species the body levels of radioactivity increased rapidly during the first few days of the exposure period, but after exposure for 7 to 8 days to sea water containing 50 g hydrocarbon/l an equilibrium condition was approached; in some experiments where E. affinis was exposed to 1.0 and 10 g hydrocarbon/l for 15 days there was no further increase in body levels of radioactivity after 7 to 8 days. Using a low concentration of hydrocarbon (1 g/l), the quantity of radioactivity accumulated after 10 days was found to be nearly fifty times greater in the smaller species, E. affinis, than in C. helgolandicus, when expressed in terms of body weight. After they had been exposed to the hydrocarbon for several days the copepods contained a considerable proportion of radioactivity that was no longer identifiable as naphthalene and was presumably present as metabolites. Radioactivity accumulated in the copepods after several days was rapidly lost after they were transferred to uncontaminated sea water: e.g. C. helgolandicus lost nearly 90% of its body level of radioactivity in 24 h. Thereafter the rate of loss was greatly reduced, and 5% of the original body level of radioactivity still remained in the copepods at the end of 11 days. Experiments on the breakdown of naphthalene added at low concentrations to sea water samples containing natural microbial populations indicated degradation rates of 0.1 to 0.2 g/l/24 h in oceanic water, and 2.6 g/l/24 h in inshore water samples. The results are discussed in terms of the possible transfer of hydrocarbon to a higher trophic level in areas subjected to constant low-level inputs of petroleum hydrocarbons.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Feeding ecology of the lanternfish Benthosema pterotum from the Indian Ocean

The feeding ecology of lanternfish Benthosema pterotum (Alcock) from the north Arabian Sea, Mozambique and the Bay of Bengal was studied. Samples were collected on cruises carried out by R.V. Dr. Fridtjof Nansen during the period 1978 to 1983. A wide variety of zooplankton organisms were identified in the diet of B. pterotum with crustanceans dominating the diet. Copepods constituted ca. 40 to 90% of the diet. Dry weight analyses of the stomach contents from the Gulf of Oman in February 1983 showed copepods to be 35 to 55% in weight (average in samples). Ontogenetic differences were observed in the diet. Prey size increased as the fish length increased, but the largest fish did not exclude the smaller prey organisms from their diet. Regional variation in diet was also shown in B. pterotum. The degree of filling and the state of digestion of stomach contents revealed that this species feeds intensively at night in the epipelagic layer. All copepods indentified were epipelagic species, providing additional evidence of diurnal pattern in the feeding chronology of B. pterotum. Identification of copepods from the Gulf of Oman in February 1983, revealed that herbivorous species dominated in biomass. Quantitative analyses show that B. pterotum probably have a daily food intake of ca. 4.5% of the body weight.     

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 m in diameter in food environments dominated by nanoplankton (<5 m).     

Feeding rates and diel vertical migration of copepods near South Georgia: comparison of shelf and oceanic sites

Seventeen Longhurst Hardy Plankton Recorder profiles were taken over a diel cycle in January 1990 to study the feeding of four major copepods over the South Georgia shelf. Ontogenetic changes in vertical migration were followed and feeding cycles determined by gut fluorometry for Calanoides acutus Stage CV, Calanus sinillimus CV and CVI, C. propinquus CV and Rhincalanus gigas CV and CVI. In common with a neighbouring oceanic site visited two weeks later and reported elsewhere, all four species had a diel cycle of feeding and migration. The vertical distributions of C. simillimus (all stages), R. gigas (nauplii) and Euphausia frigida (postlarvae) were similar at both sites, the night being spent within the chlorophyll maximum at 15 to 30 m. However, the biomass dominants, C. acutus and R. gigas, dwelt below the chlorophyll maximum, about 30 m deeper than their oceanic counterparts. Unlike the oceanic site, feeding at the shelf site was not restricted to darkness, but increased 6 to 10 h before nightfall and finished at dawn; the intervening period coincided with sinking and digestion. Daylight feeding may have been induced by the shorter night, lower light levels or greater food requirements at the shelf site, despite planktonic predators being over three times more abundant. Daily ration estimates for R. gigas at both sites were only 2% body carbon per day. These low values contrast with its smaller competirors, whose rations were in the range 5.6 to 27%.     

Daily ration and specific daily ration of the chaetognath Sagitta enflata

Digestion times, obtained directly from laboratory feeding, were used in conjunction with a day/night series of field samples to estimate the daily ration and specific daily ration of Sagitta enflata Grassi, the most abundant chaetognath in the Gulf Stream near Miami, Florida (USA), during winter and early spring. Feeding was independent of time of day and increased with increasing chaetognath size from 1.7 prey day^-1 for the 11.5 mm size class to 2.9 prey day^-1 for the 21.5 mm class. The diet of s. enflata consisted of 94.8% copepods having a mean weight of 21.8 g, and 5.2% prey chaetognaths estimated to be two-thirds the length of the predators. The daily ration of S. enflata from 12.5 to 20.5 mm in length increased from 48.3 to 143.3 g of prey dry weight and from 18.5 to 48.1 g of prey carbon. The specific daily ration declined from 0.12 to 0.08 dry weight basis, and from 0.26 to 0.14, carbon basis, over the same size range. Prey chaetognaths contributed as much as 51% of the ration on a carbon basis.     

Direct sampling and in situ observation of a persistent copepod aggregation in the mesopelagic zone of the Santa Barbara Basin

Observations from a one-person submersible (Wasp) in fall, 1982, revealed a persistent aggregation of non-migrating, Stage V copepodites of Calanus pacificus californicus Brodsky in a band 20±3 m thick at a depth of 450 m, about 100 m above the bottom of the Santa Barbara Basin, California. Copepod abundances, calculated from nearest-neighbor distances measured directly from the submersible, yielded maximum densities of 26×10⁶ copepodites m^-3. Quiescent behavior, low laminarinase activity, low protein content, high lipid content and evidence of low excretion rate all suggest that these copepodites were in a state of diapause. Diapausing C. pacificus californicus at other locations along the eastern Pacific coast were also captured in discrete depth plankton tows. Both the submersible observations and the net collections suggest that the dense aggregation of diapausing copepods we observed in the Santa Barbara Basin was a phenomenon associated with seasonal upwelling cycles, and that such aggregations occur during non-upwelling periods when food is scarce in surface waters. Numerous predators, especially the deep sea smelt Leuroglossus stilbius, were observed feeding upon the aggregated copepods; thus, in contrast to the conventional picture of surface-dominated food distribution, deep-water aggregations of C. pacificus californicus may support the mesopelagic community during periods of low food availability in surface waters.     

Transformation of soft coral (Coelenterata: Octocorallia) terpenes by Ovula ovum (Mollusca: Prosobranchia)

The faecal pellets from specimens of the prosobranch mollusc Ovula ovum found feeding on the soft coral Sarcophyton sp. at Eclipse Island, Palm Island Group (18°46S; 146°33E) in November 1980 were analysed. The only terpene present in the faeces, 7,8-deoxysarcophytoxide, differed from the major constituent of the soft coral, sarcophytoxide, suggesting that the latter had been transformed into the former within the cowrie. This transformation is not trivial, and could not be produced simply by acid catalysis. Subsequent analysis of tissues dissected from different regions of O. ovum indicates that the transformation is probably effected by enzymes in the digestive diverticula stomach region of the prosobranch. The transformed compound is significantly less toxic to the mosquito fish Gambusia affinis Baird and Girard than the ingested compound.     

Ecological constraints on the behaviour of mother long-tailed macaques (Macaca fascicularis)

Summary The ecological consequence of the effects of different social conditions on the behaviour of females with infants were examined in two different-sized groups of long-tailed macaques (Macaca fascicularis) that inhabited adjacent home ranges in Gunung Leuser National Park in Indonesia. This study aims to test predictions of the within-group competition/predation avoidance hypothesis of social organization. Females, particularly those carrying an infant, are considered to experience the most direct effects of environmental constraints on fitness prospects. Data on maintenance behaviour, height in canopy and spatial position were collected for five mothers in a small group and eight mothers in a large group. Comparisons were made on the basis of group size and dominance rank. Mothers from the large group spent less time feeding on clumped fruits and more time foraging on dispersed food items. Lower-ranking mothers, undergoing the highest rate of within-group competition, foraged most. For macaques in the study area, predation risk is considered to decrease with height in the canopy. Mothers in the small group, assumed to be more susceptible to predation, remained substantially higher in the canopy than mothers in the large group. In both groups, mothers adjusted their height to their spatial position in the group. Lower-ranking mothers were more often found without neighbours, presumably to avoid feeding competition. As a result they stay higher in the canopy than higher-ranking mothers. The results clearly demonstrate that individual females in the same reproductive state and living in the same area, but in different social environments, adapted their behaviour according to the hypothesis. Correspondence to: D.R. Vos     

Diel changes in gut-cell morphology and digestive activity of the marine copepod Acartia tonsa

Morphometric measurements of the gut cells of the marine calanoid copepod Acartia tonsa were made over a 24 h diel cycle to test the hypothesis that feeding rhythms in this copepod are limited by the cycles of blishter-like cells (B-cells) in the gut. Copepods were collected from Long Island Sound, New York, USA, in June 1991. Experimental treatments included low (1 g chlorophyll al^-1) and high (10 g chlorophyll al^-1) food concentrations. Copepods were fixed and embedded in Epon at six time intervals over the 24 h period, and semi-thin sections through the length of Midgut Zone II were analyzed for gut-cell area and vacuole area, with area measurements integrated to yield estimates of gut-cell volume and vacuole volume. Concurrent measurements of gut fluorescence, a measure of gut fullness, and digestive enzyme activities also were made. A diel cycle in gut fluorescence was observed, most notably in the low-food treatment, which exhibited a 3-fold increase in gut pigments. There was little consistent change in digestive enzyme activities over this time span. Gaps in the gut wall indicative of spent B-cells were observed in 17 of 39 copepods, with no trend over time or food treatment. Generally, only a single gap was seen in any one copepod. B-cells were vacuolated throughout the 24 h period. Morphometric analyses revealed a correlation between gut fluorescence and both maximum vacuole area and vacuole volume, as well as percent vacuolated cell volume, in the low-food treatment. The high-food treatment, which had a relatively smaller increase in gut fluorescence (1.5-fold) during the night cycle, showed no significant increase in vacuole size. B-cells appear to have a life-cycle greater than the diel feeding period, and while B-cell vacuoles respond to the ingested food during the diel cycle, production of B-cells does not appear to be a limiting factor in A. tonsa's feeding cycle.     

Grazing rates of the Atlantic menhaden Brevoortia tyrannus as a function of particle size and concentration

The feeding behavior of adult Atlantic menhaden (Brevoortia tyrannus) upon 5 species of phytoplankton and 2 species of zooplankton has been studied. Four recognizable feeding stages which were a function of the concentration and size of the food particles were observed. During rapid feeding the fish swam at a constant speed for a prolonged period over a wide range of particle concentrations. Particle and food carbon-concentrations at the threshold for initiation and termination of feeding were inversely related to particle size. Carteria chuii (13.2 μ) was not grazed at a significant rate, while two-cell chains of Skeletonema costatum (16. 5 μ) were filtered from the water, indicating a minimum-size threshold for filtration of between 13 and 16 μ. The most rapid filtering rates were observed for the copepod Acartia tonsa ( \(\bar x\) volume swept clear = 24.8 l/fish/min). The maximum food-particle size acceptable to a menhaden appears to be between Acartia tonsa (1200 μ) and adult Artemia salina (10 mm). These results suggest that the large schools of menhaden found in Atlantic coastal waters could have a significant effect on the plankton, selectively grazing zooplankton, larger phytoplankton, and the longer chains of chain-forming diatoms.     

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.     

Digestive carbohydrases from the hepatopancreas of two Antarctic euphausiid species (Euphausia superba and E. crystallorophias)

The hepatopancreatic extracts of Euphausia superba Dana and E. crystallorophias Holt and Tattersall collected from the Antarctic. Ocean during January 1985, are most effective in hydrolysing substrates containing (13)--glucosidic linkages. Three enzymes appear to be involved in the depolymerization of (13)--D-glucans in the euphausiid diet: (1) an exo-(13)--D-glucanase, (2) an endo-(13)--D-glucanase and (3) a -D-glucosidase. The glucanases have a pH optimum of 5.4, a temperature optimum of 50°C and are optimally extracted in bistripropane buffer, pH 7.2. Levels of (13)-D-glucanase in laboratory-cultured E. superba are inversely affected by food availability, and activities double after starvation for 12 d. The increase is due mainly to higher activities of exo-acting glucanases. -Amylase and endo-(14)--D-glucanase (cellulase) activity are also present in the extracts in addition to glycosidase activity against a range of p-nitrophenyl substrates (-and -D-glocose, - and -D-galactose, -D-xylose, - and -D-mannose). Digestive activity against several acidic polysaccharides, including the acidic mucilage polysaccharide of the ice diatom Stauroneis amphioxys, is minimal and is not induced when the polysaccharide is present in the diet of E. superba. These results indicate that some, but not all, components of the algal material in the euphausiid diet can be hydrolyzed and assimilated.     

Omnivorous feeding behavior of the Antarctic krill Euphausia superba

Feeding experiments were conducted at Palmer Station from December 1985 to February 1986 to examine the potential role of copepod prey as an alternative food source for Euphausia superba. Copepod concentration, copepod size, phytoplankton concentration, the duration of krill starvation and the volume of experimental vessels were altered to determine effects on ingestion and clearance rates. Krill allowed to feed on phytoplankton and copepods in 50-litre tubs showed greatly increased feeding rates relative to animals feeding in the much smaller volumes of water traditionally used for krill-feeding studies. Clearance rates on copepods remained constant over the range of concentrations offered, but clearance rates on phytoplankton increased linearly with phytoplankton concentration. Feeding rates increased when larger copepods were offered and when krill were starved for two weeks prior to experiments. Clearance rates of krill feeding on copepods were higher than, but not correlated with, their clearance rates on phytoplankton in the same vessel. E. superba may have a distinct mechanism for capturing copepods, perhaps through mechanoreception. Although our observed clearance rate of 1055 ml krill^-1 h^-1 indicates that krill can feed very efficiently on copepod prey, such feeding would meet less than 10% of their minimum metabolic requirements at the typical copepod concentrations reported for Antarctic waters. However, substantial energy could be gained if krill fed on the patches of high copepod concentrations occasionally reported during the austral summer, or if krill and copepods were concentrated beneath the sea ice during the winter or spring months. Our results, indicating efficient feeding on zooplankton and higher clearance rates on phytoplankton than previously believed, represent a step towards balancing the energy budget of E. superba in Antarctic waters.     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic II. Sternoptychidae

The vertical distribution of seven sternoptychid species was examined from RMT 1+8 samples collected aboard R. V. Meteor in March-April 1979 and from Royal Research Ship R.R.S. Discovery in July 1974 in the central equatorial Atlantic. During daytime sternoptychids occupied depths between 200 and 1250 m, with Sternoptyx pseudobscura living deepest, centering between 800 and 900 m, and Argyropelecus sladeni most shallow, aggregating predominantly at 300 and 400 m. They are all considered limited or partial migrants, ascending only some 100 and 200 m towards the surface at night. Only A. sladeni was observed to enter the epipelagic zone (0 and 200 m).-Feeding patterns were investigated from stomach content analyses of Sternoptyx diaphana, S. pseudobscura, Argyropelecus sladeni and A. affinis. Additional stomach contents were analysed from samples of S. diaphana, A. hemigymnus and A. olfersi collected in June 1985 from F.R.V. Walther Herwig in the temperate NE Atlantic at 46°N, 17°W by means of the Engel Trawl. The food spectrum of the six species is generally described, and additional dietary evidence regarding calanoid copepod prey is provided for four of these taxa. All sternoptychid species investigated were planktivorous, feeding predominantly on copepods and ostracods, except for the largest size class, which preyed heavily on euphausiids and amphipods. The relationship of predator size towards prey type and prey size is analysed for both Sternoptyx species. Of these, S. pseudobscura in particular exhibits taxonomic selectivity towards polychaete prey. The diet of both species of Sternoptyx included a number of epipelagic or even neustonic calanoid copepod species which contributed more than 50% of the total copepod population by numbers. So far it is not known how the predators find access to prey organisms of the upper 200 m, as netfeeding is considered unlikely. Cyclopoid copepods of the genus Sapphirina were observed as dietary component particular of S. diaphana.