Ontogenetic shifts and temporal changes in the trophic patterns of the deep‐sea red shrimp,Aristaeomorpha foliacea (Decapods: Aristeidae), in the Eastern Ionian Sea (Eastern Mediterranean)

The purpose of this paper is to provide the first detailed data concerning the diet and feeding activity of the giant red shrimp, Aristaeomorpha foliacea, in the Eastern Ionian Sea (Eastern Mediterranean), in relation to season, size class and sex. Feeding activity in A. foliacea was intense, based on its low vacuity index and high prey diversity, with a diet dominated by mesopelagic prey and less frequent occurrence of benthic taxa. Giant red shrimp displayed a highly diversified diet that exhibited slight seasonal fluctuations. The diets of both sexes consisted of 60 different prey categories belonging chiefly to three groups: crustaceans (e.g. decapods, such as Plesionika spp. and Pasiphaeidae, amphipods), cephalopods (mainly Enoploteuthidae) and fishes (Myctophidae, Macrouridae). These three prey categories accounted for 72–82% of the relative abundance and total occurrence for males and 70–88% for females, respectively. Variation in food availability, as well as increased energy demands related to gonad development and breeding activity, appear to be critical factors driving temporal changes in feeding strategy. Feeding activity increased during spring and summer, which coincides with reproductive activities (mating, gonad maturation, egg‐laying). Females seem to be more active predators than males, consuming prey with greater swimming ability. However, ontogenetic shifts in diet were also apparent, despite high dietary overlap among small, medium and large females. Large individuals, which are more efficient predators, selected highly mobile prey (e.g. fishes), whereas small individuals consumed low‐mobility prey (e.g. copepods, ostracods, tanaids and sipunculans).     

Trophic relationships in tidepool fish assemblages of the tropical Southwestern Atlantic

Trophic studies are fundamental to understanding the dynamics of assemblages and functional roles of species within ecosystems, contributing to the identification of factors responsible for the organization and structure of communities. This study aimed to analyse the trophic organization of tidepool fish assemblages in the tropical Southwestern Atlantic, based on the underlying idea that food resources are not limiting and that trophic guild formation is not driven by food competition. Diets were based on feeding index values of food categories for 12 representative species collected in six tidepools (20º49′ S, 40º36′ W) at quarterly intervals (2005 to 2007). The main food categories were small crustaceans, polychaetes and macroalgae. Multivariate techniques evidenced two multispecific trophic guilds: small‐prey carnivores, including Bathygobius soporator, Bathygobius geminatus, Malacoctenus delalandii and Halichoeres poeyi, and herbivores, including Sparisoma axillare and Acanthurus bahianus. Other species presented significantly different diets and were classified into the following guilds: omnivores feeding on filamentous algae and copepods (Abudefduf saxatilis); large‐prey carnivores (Labrisomus nuchipinnis); omnivores feeding on polychaetes and filamentous algae (Stegastes fuscus); and polychaete feeders (Ahlia egmontis). Gymnothorax funebris and Gymnothorax moringa were classified as carcinophagores and piscivores, respectively. Trophic organization appears related to species convergence toward the use of abundant food resources, driven by a combination of factors allowing some resource partitioning through inter‐specific differences in consumer size, microhabitat, behavior, and trophic specialization.     

The food and feeding of seven fish species from the Campbell Plateau,New Zealand

The food and feeding habits of hoki (Macruronus novaezelandiae), southern blue whiting (Micromesistius australis), javelin fish (Lepi‐dorhynchus denticulatus), ling (Genypterus blacodes), smooth rattail (Coelorinchus aspercephalus), silverside (Argentina elongata), and small‐scaled notothenid (Notothenia microlepidota) sampled from the Campbell Plateau in 1979 were examined. The importance of prey items in the diet has been assessed by an ‘index of relative importance’, which combines measurements of frequency of occurrence, number, and weight of prey. Hoki, southern blue whiting, and javelin fish are pelagic feeders. Hoki preyed largely on natant decapod crustaceans, amphipods, and myctophid and photichthyid fishes. The main prey of southern blue whiting were amphipods, natant decapods, and euphausiids. Javelin fish fed on natant decapods, amphipods, and small squid. Seasonal and regional differences in feeding, and dietary changes with length of fish were evident. Ling, smooth rattail, silverside, and small‐scaled notothenid are predominantly benthic feeders. Ling preyed on natant decapods, macrourid fishes, and small hoki. The diet of rattail comprised natant decapod crustaceans, opal fishes (Hemerocoetes spp.), and poly‐chaetes. Silverside fed almost solely on salps. Salps, amphipods, brachyuran crustaceans, and opal fishes were the main prey of small‐scaled notothenid.     

Assessing trophic adaptability is critical for understanding the response of predatory fishes to climate change: a case study of Pomatomus saltatrix in a global hotspot

There is a growing need to incorporate biotic interactions, particularly those between predators and their prey, when predicting climate-driven shifts in marine fishes. Predators dependent on a narrow range of prey species should respond rapidly to shifts in the distribution of their prey, whereas those with broad trophic adaptability may respond to shifts in their prey by altering their diet. Small pelagic fishes are an extremely important component of the diet of many marine predators. However, their populations are expected to shift in distribution and fluctuate in abundance as the climate changes. We conducted a comparative study of the seasonal diet of adult Pomatomus saltatrix over two periods (June–December 2006 and 2012) and examined the available data on small pelagic fishes biomass in a global hotspot (the coastal region of southern Angola, southern Africa) to gain an understanding of the tropic adaptability of the species. Despite a drop (630 000 t to 353 000 t) in the abundance of their dominant prey (Sardinella aurita) in the region, it remained the most important prey item during both study periods (Period 1 = 99.3% RI, Period 2 = 85.3% RI, where %RI is a ranking index of relative importance). However, the diet during Period 2 was supplemented with prey typically associated with the nearshore zone. The seasonal data showed that P. saltatrix were capable not only of switching their diet from S. aurita to other prey items, but also of switching their trophic habitat from the pelagic to the nearshore zone. These findings suggest that P. saltatrix will not necessarily co-migrate if there is a climate-driven shift in the distribution of small pelagic fishes (their dominant prey). Accordingly, understanding the trophic adaptability of predators is critical for understanding their response to the impacts of climate change.     

Feeding ecology,diet and field-based studies on feeding selectivity of the Cape anchovy Engraulis capensis Gilchrist

Samples collected during four cruises on board R.S. Africana were used to study the trophic ecology and feeding behaviour of Engraulis capensis in the southern Benguela region. Previous work had indicated that this species was a non-selective filter-feeding omnivore, diatoms comprising the bulk of the diet. The results of the present study reveal that anchovies selectively feed on mesozooplankton, especially calanoid copepods and euphausiids. Investigation of the feeding behaviour of the species indicates that raptorial feeding is dominant over filter-feeding and that prey appears to be selected primarily on the basis of size.     

Trophic ecology of Pomatoschistus microps within an intertidal bay (Roscoff,France), investigated through gut content and stable isotope analyses

The diet of Pomatoschistus microps has been studied using both gut content and stable isotope analyses. In the Roscoff Aber Bay (Brittany, France), this fish is commonly found on sandy muddy intertidal flats. Gut content analyses were also interpreted using trophic indices. Owing to the large diversity of prey consumed, these indices emphasised the opportunistic feeding behaviour of P. microps. Here, this species fed mainly on endofauna with meiofauna being of high relative importance. The main biotic components of its trophic habitat, characterized by δ¹³C and δ¹⁵N, provided evidence of a major trophic pathway based on drift Enteromorpha sp. Trophic positions estimated by both diet analyses and isotopic analyses led to similar results. In this bay, P. microps is a first‐order predator with a low degree of omnivory. Despite a preferential consumption of the amphipod Corophium arenarium, we assumed that this goby behaves as a generalist feeding on a uniform variety of endofauna taxa.     

Food and feeding habits of Octopus insularis in the Veracruz Reef System National Park and confirmation of its presence in the southwest Gulf of Mexico

Octopuses are active predators that feed on a wide range of prey including crustaceans, fishes, and mollusks. They are important components of coral reef systems and support local and artisanal fisheries in the Gulf of México. Octopus insularis has been found to be one of the most relevant components in catches from the coral reef system of Veracruz in the southwestern Gulf of Mexico, and its role in the ecosystem requires assessment. To corroborate the morphological identification of O. insularis, six octopuses were identified by genetic methods. And to understand the trophic relationships between this octopus species and its prey, 394 octopuses caught during 2016 and 2017 by an artisanal fleet were sampled and their stomach contents analyzed. Results showed that crustaceans are the most frequently consumed group, with the genera Mithraculus and Etisus being the most important in the diet. Fishes, bivalves, and gastropods were identified as uncommon prey items in the diet. Their presence in the stomachs could be related to the movement of this octopus outside of the coral reef. Considering that our samples were of medium‐ and large‐sized individuals, cannibalism could be discarded for O. insularis in this size range in the Veracruz reef system. These findings suggest a generalist and opportunistic predation of O. insularis on the most abundant and available prey in the study area, namely the crustaceans. These represents an effective transfer of biomass from the low trophic levels to top predators in the coral reef system.     

Size-dependent, Spatial, and Temporal Variability of Juvenile Walleye Pollock (Theragra chalcogramma) Feeding at a Structural Front in the Southeast Bering Sea

Abstract. The waters surrounding the Pribilof Islands are an important nursery ground for juvenile walleye pollock (Theragra chalcogramma), an important forage fish in the pelagic food web of the productive Bering Sea shelf region. The diet of juvenile pollock was studied in two consecutive years along a transect line crossing from a well‐mixed coastal domain, through a frontal region to stratified water farther offshore. Variability in stomach fullness was high and evidence for increased feeding intensity in the front was weak. Prey diversity and prey size generally increased with increasing fish size, shifting from predominantly small copepods to larger, more evasive prey items such as euphausiids, crab megalopae and fish. The diet of the fish reflected changes in the relative abundance of copepods and euphausiids in the prey fields between years. Juvenile pollock showed increased feeding rates at dusk, and stomach fullness as well as prey condition were generally lowest just before sunrise; however, the proportion of euphausiids increased in the diet of pollock caught at night, suggesting that some food was also ingested during darkness. Juvenile pollock and their euphausiid prey both vertically migrated above the thermocline at night, although each had a different daytime depth.     

Evaluation of food competition and resource partitioning of recruiting fish with permanent residents in a seagrass habitat

ABSTRACT

Recruiting King George whiting Sillaginodes punctatus were studied to assess the potential for food competition with permanent resident fish species in a nursery habitat. Marine migrant post larval S. punctatus (<60?mm TL) consumed primarily harpacticoid copepods and had high (>0.6) diet overlap with permanent resident fish species Favonigobius leteralis and Stigmatopora nigra. Food electivity index indicated that S. punctatus juveniles preferred harpacticoid copepods and amphipods, while juvenile Heteroclinus adelaide and Gymnapistes marmoratus migrating to the nursery habitat targeted larger prey such as amphipods. Preference for larger prey by H. adelaide and G. marmoratus species coupled with differences in prey composition in the stomach was due to mouth size and feeding habits, resulting in different food preferences to S. punctatus. The whiting showed an ontogenetic shift in diet with early settlers (>60?mm TL) consuming less copepods and more amphipods, while previous year recruits (>120?mm TL) consumed polychaete worms. This study indicates that competition for food resources between the new recruiting S. punctatus juveniles and permanent resident juveniles is reduced through differences in temporal and spatial feeding behaviours, mouth morphology, and ontogenetic shift in prey consumption.     

Adaptation of diet in a changed environment: Increased consumption of lobster krill Munida gregaria (Fabricius, 1793) by Argentine hake

A well‐replicated decadal‐term (2005–2014) stomach content data set was analysed in order to infer inter‐annual fluctuations in the diet of the Argentine hake, Merluccius hubbsi, an opportunistic predator in the San Jorge Gulf (SJG) ecosystem in the Southwest Atlantic. Ten research cruises were carried out each year during January from 2005 to 2014. A total of 18,461 specimens of Me. hubbsi was analysed, of which 6,777 (36.71%) contained food in their stomachs. The diet of Me. hubbsi changed markedly from 2011 onwards, with much greater consumption of the lobster krill Munida gregaria compared to the years before 2011. The frequency of occurrence (%F) of Mu. gregaria in the stomach contents of Argentine hake increased from the year 2009 onwards, most noticeably since 2011, and mostly over the southern region of the SJG. The main predators of Mu. gregaria in the SJG are two species of teleost fish (pink cusk eel, Genypterus blacodes, Argentine seabass, Acanthistius brasilianus) and three Rajidae skates (Zearaja chilensis, Psammobatis spp. and Sympterygia bonapartii), which exhibited decreased catches in the years analysed. The increased consumption of Mu. gregaria by Me. hubbsi, coupled with decreased trends in abundance of the main predators of the lobster krill during the last decade, indicate that top‐down trophic dynamic control occurs in the SJG ecosystem.     

Food and feeding of small fish in the Rakaia River,New Zealand

Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12‐month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.     

Spatial, temporal and ontogenetic variation in diet of anchovy (Engraulis encrasicolus) on the Algerian coast (SW Mediterranean)

The diet of anchovy Engraulis encrasicolus was studied in three regions (Béjaia, Bénisaf and Ghazaouet) along the Algerian coast. Ontogenetic, spatial and seasonal variations in anchovy diet were investigated using multivariate analyses and analysed in relation with sea surface temperature and chlorophyll-a. 46 prey taxa of varying size between 0.57 mm (Euterpina acutifrons) and 6.8 mm (fish larvae) were recorded. Whatever the season, the region or the fish size, anchovy is exclusively zooplanktivorous and copepods were the most present prey, constituting 87% by number of the prey taken and found in 98% of the anchovy stomachs examined. However, their occurrence and number varied according to the different areas, seasons and fish size. During its first year of life, anchovy feeds almost exclusively on copepods (mainly small and medium size prey). As anchovy grows, copepods are gradually substituted by large crustaceans such as decapods and amphipods. Hierarchical cluster analysis, analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated a distinct diet of anchovy of the bay of Bejaia from those of the bays of Bénisaf and Ghazaouet probably due to differences in hydrologic conditions. Diet differences also occurred between seasons. Summer and spring have distinct prey assemblages each and showed low diet similarities with the two other seasons. More prey species were found in the diet during winter (36) and autumn (30) and the vacuity index was lower in winter. Temporal variability in satellite-derived chlorophyll-a matched the seasonal variability in the diversity of the anchovy prey and feeding intensity as reflected by the vacuity index, suggesting further investigation of the potential use of satellite-derived chlorophyll-a data as a proxy for anchovy feeding intensity.     

Food preferences and rhythms of feeding activity of two co‐existing demersal fish,the longspine snipefish,Macroramphosus scolopax (Linnaeus, 1758), and the boarfish Capros aper (Linnaeus, 1758), on the Mediterranean deep shelf

The feeding behaviour of two potentially competing species, the longspine snipefish, Macroramphosus scolopax, and the boarfish Capros aper was examined. While both species are very abundant along the Mediterranean coast and are regularly caught by demersal trawlers, they are of no commercial value. The diets of boarfish and longspine snipefish were investigated from samples collected between January 2001 and May 2002. Variations in the diet with fish size and season, as well as diet overlap and diversity were explored. Mysid shrimps, amphipods and gastropods were the most important food items in the diet of longspine snipefish. During ontogenetic development, M. scolopax occupies different trophic levels: the diet shifts from being predominantly composed of mysids (Anchialina agilis, Lophogaster typicus, Erythrops sp., Leptomysis spp.) in the smaller longspine snipefish [<6.5 cm total length (TL)] towards decapods (Anapagurus laevis) and amphipods (Leucothoe incisa, Eusirus longipes, Hyperidea) in the larger individuals (>6.5 cm TL). Crustacean decapods and copepods were the most important prey in the stomachs of boarfish. Mysids (Lo. typicus), euphausiids and nematodes were present in the larger individuals (>8 cm TL). A more generalist diet, still containing copepods, crustacean decapods, gastropods (Limacina retroversa) and a large variety of amphipods (e.g. Phtysica marina, Stenotoe bosphorana) and mysids (e.g. A. agilis, Leptomysis spp., Erythrops sp.), dominated the diet of C. aper between 2 and 8 cm TL. Diet overlap between longspine snipefish and boarfish was very low and the differences in stomach species diversity were explained by season and fish size.     

Diet composition and resource partitioning in two small flatfish species in the German Bight

Since the late 1980s, the small-sized non-commercial flatfish species solenette (Buglossidium luteum) and scaldfish (Arnoglossus laterna) have increased in abundance in the southern North Sea. Because these species are considered as possible competitors for prey of commercial flatfish, this study aimed at advancing knowledge of their feeding ecology.Between January 2009 and January 2010 stomach contents of solenette and scaldfish and benthic infauna were sampled seasonally in a study area in the German Bight. The objectives were to investigate the seasonal variability of feeding activity and diet composition of both flatfish species related to benthic prey availability.For both flatfish, the highest feeding activity was found in summer, at the same time that the highest prey densities occurred in the study area. A reduced feeding activity was observed during the winter of 2010, but not in the winter of 2009, probably related to higher 2009 water temperatures.In all seasons, diet composition of solenette was dominated by meiofauna, mainly harpacticoid copepods. Macrofauna prey species, namely juveniles of bivalves and echinoderms became important in spring. An increase in amphipods and cumaceans was found in the stomach contents during summer and autumn, simultaneously with their increased abundance in the benthic infauna. In contrast, polychaetes were rarely found in the diet, but dominated the infauna during all seasons.Diet composition of scaldfish was dominated by larger and mobile prey, and, during all seasons, was mainly comprised of crustaceans. Amphipods characterised the diet in both winters, while decapods such as Crangon spp. and Liocarcinus spp. were the dominant prey from spring to autumn. Additionally, juveniles of flatfish (Pleuronectids) and bivalves were found in the scaldfish diet in spring, replaced by cumaceans in summer. No dietary overlap between both flatfish species was found across seasons, indicating partitioning of prey resources between solenette and scaldfish. Their different feeding strategies and prey preferences, in turn were influenced by the seasonal variability of available prey.     

Feeding ecology of the mud shrimp Solenocera melantho in the East China Sea

The feeding habits of the mud shrimp Solenocera melantho were studied in the East China Sea by analysing 720 stomach contents and comparing diet composition and prey diversity among seasons, sexes and size classes. Feeding activity was linked to season and ovarian condition. The stomach fullness was high during spring and summer and low in fall. Females with advanced ovaries also displayed low stomach fullness, which suggests that feeding activity is affected by the reproductive cycle. The diet of S. melantho consisted of 42 different prey categories, primarily smaller crustaceans, Foraminifera, polychaetes, mollusks and fishes (larvae and eggs). Crustacea,Foraminifera and polychaetes together constituted the dominant prey groups, accounting for 75% of total prey abundance and >50% of total prey occurrence. Diet composition differed among seasons between sexes and size classes. Females and males consumed the same prey items but with different orders of importance. In terms of body size, the small shrimps preferred relatively small food items, such as Foraminifera and algae, whereas larger shrimps preferred polychaetes and crustaceans. Trophic diversity varied among the seasons within both sexes and size classes, with the highest values being observed in fall. Niche overlap was high within both sexes and size classes among seasons (0.6051–0.8740).     

Responses of the chaetognath, Sagitta elegans, and larval Pacific hake, Merluccius productus, to spring diatom and copepod blooms in a temperate fjord (Dabob Bay, Washington)

As part of a broader field study examining the potentially deleterious effects of diatoms on planktonic food webs, we examined the abundance, stage composition, diet, and feeding success of the chaetognath, Sagitta elegans, and the abundance and morphometric condition of larval Pacific hake, Merluccius productus. Our objective was to look for a relationship between spring phytoplankton blooms and planktonic predators, as mediated by their copepod prey, with special reference to possible deleterious effects of diatoms. Zooplankton were collected weekly during February–May and in mid-summer of 2002 and 2003 in Dabob Bay, Washington State, USA. S. elegans abundance was high in summer of both years and was higher in spring 2003 than spring 2002. Larval chaetognaths dominated the population in early spring and remained present throughout sampling. S. elegans consumed mostly copepods. The abundance of larval S. elegans was correlated with the abundance of copepodites, although no relationship between chaetognath feeding success and prey abundance was found. Larval Pacific hake abundance was high (1200 larvae per square meter) in late February and early March of 2002 and 2003 and decreased rapidly in late spring. The morphometric condition of M. productus was not significantly related to copepod abundance. These results indicate that any deleterious effects of diatoms on copepod abundance, at the scale seen during spring 2002 and 2003 in Dabob Bay, did not greatly affect the next higher trophic level.     

Rhythms of feeding activity and food consumption of two Mediterranean burrowing fishes: Gnathophis mystax (Delaroche) and Chlopsis bicolor Rafinesque

Data on the food consumption, feeding activity and periodicity of two burrowing fish, the congrid eel Gnathophis mystax (Delaroche, 1809) and the false moray Chlopsis bicolor Rafinesque, 1810 are presented. In all, 455 specimens were collected by bottom trawl in the central Mediterranean Sea at depths ranging from 140 to 160 m during four 24‐h day–night sampling cycles. The diet of G. mystax and C. bicolor was investigated by means of stomach content analysis. Diet varied significantly with length and maturity stage. During ontogenetic development G. mystax occupied different trophic levels: diet shifted from amphipods, predominantly in the smaller congrid eels [<25 cm total length (TL)] to fish in the larger individuals (>30 cm TL). Before the transition to the icthyophagous phase, the congrid eel showed a more generalistic foraging behaviour where decapods (Solenocera membranacea, Parapenaeus longirostris, Alpheus glaber), cephalopods (Sepiola spp. and Alloteuthis media), benthic (Gobiidae, Callionymus maculatus, Arnoglossus laterna) and benthopelagic fish (Argentina sphyraena) dominated the diet. Smaller C. bicolor (<25 cm TL) fed primarily on amphipods and cephalopods; bigger specimens fed also on decapods both natantian (A. glaber, Processa canaliculata) and reptantian (Medorippe lanata, Goneplax rhomboides). Daily ration values, computed from the Eggers method, ranged from 2.48% to 2.99% wet body weight for C. bicolor and G. mystax, respectively. Diel patterns in stomach fullness and the trophic niche overlap between the two species were also discussed.     

Characterisation of the dietary relationships of two sympatric hake species,Merluccius capensis and M. paradoxus,in the northern Benguela region using fatty acid profiles

The two sympatric species of Cape hake, Merluccius capensis and M. paradoxus, have been the main targets of bottom-trawl fisheries off Namibia for several decades. The feeding ecology of these hakes has been studied mainly using stomach content analyses and thus there remain some gaps in our knowledge about food assimilated over the longer term. In this study, we used fatty acid (FA) profiles to characterise the dietary relationships of M. capensis and M. paradoxus. Muscle samples from hake (n=110) and their known prey (n=68) were collected during trawl surveys off Namibia during 2011. Significant differences between the neutral FA profiles of the hake populations were detected in December 2011 but not in January 2011, an indication of temporal variations in diet and resource partitioning. Comparisons of the neutral FAs in hake and the total FAs of potential prey showed no clear trophic connections, with the exception of flying squid Todarodes sagittatus, which had FA profiles very similar to those of M. paradoxus in December 2011. Our results highlight the complex and temporally shifting relationships that exist between hake and the large pool of prey available to them, and between the two hake species that overlap in their feeding habits and distribution within the highly productive Benguela Current region.     

Trophic relationships in the demersal fish community off Namibia

The benthic fish community off Namibia (between the Cunene River and Walvis Bay) in 50–650 m of water was studied during three bottom trawl surveys. The community was investigated on the basis of distribution, abundance and diet of 51 species, constituting 95 per cent of the demersal fish biomass. Dietary studies revealed the existence of three major trophic groups, one containing species that prey on pelagic and nektonic organisms, a second dominated by predators that feed on benthic polychaetes and copepods and a third group containing predators of benthic crabs, demersal shrimps and fish. Well differentiated from these groups are a few species that prey mainly on jellyfish and ophiuroids. Because for most of the species, their trophic level changes with growth, they were divided into size classes which are analysed independently. To describe interactions between the size classes, a similarity index combining diet affinity with spatial coincidence was applied. Cluster analysis showed that, for Merluccius capensis, Raja straeleni, R. clavata and Trachurus trachurus, there is a large difference in both geographic distribution and dietary preference between the size classes. For species such as Hoplostethus atlanticus, Austroglossus microlepis and Coelorinchus flabellispinis, the different size classes seem to share the same ecological niche. Variation in the number of species and the parameters mean abundance and niche width are described to enhance knowledge of the general structure of the community.