Feeding habits of the spotted flounder Citharus linguatula off the eastern coast of Spain

The composition of the diet of Citharus linguatula (L.) off the coast of the Gulf of Valencia, Spain, was determined between October 1989 and October 1990. The percentage of empty stomachs remained constant throughout the year, except for the period August to September, when a maximum was recorded coinciding with the reproductive period. Crustaceans (Mysidacea and Decapoda) and teleosts constituted the main prey. The composition of the prey ingested varied with predator size; small specimens contained a greater number of mysids in their stomachs, while decapods and fishes were more abundant in the stomachs of larger specimens. Diets varied seasonally: mysids were more important during autumn, whereas decapods were more important during winter and spring. Fishes were numerically most important in the diet in summer, but the frequency of occurrence was constant throughout the year.     

Diet composition and feeding intensity of horse mackerel,<Emphasis Type="Italic"> Trachurus trachurus</Emphasis> (Osteichthyes: Carangidae) in the eastern Adriatic

Diet composition and feeding intensity of the horse mackerel, Trachurus trachurus, collected in the eastern Adriatic Sea, were examined. Stomach contents of 1,200 specimens, taken at monthly intervals (January–December 1996), were analyzed. The stomachs contents consisted of five major prey groups: Crustacea (Euphausiacea, Mysidacea, Decapoda), Cephalopoda and Teleostei. Euphausiacea constituted the most important food resource by weight, number and frequency occurrence. Teleosts were the second most important food category, while mysids, decapods and cephalopods were occasional food. There was little seasonal variation in diet. Euphausiids were dominant prey during all seasons, and were especially abundant from spring and autumn. Feeding intensity of horse mackerel varied during the year. The lowest intensity of feeding was recorded in winter (February, March) and early spring (April) during the lower sea temperature as well as at the time of intensive spawning. Feeding activity increased upon spawning period (May and June) and was also higher during summer. Feeding intensity and diet composition changed during the diurnal cycle. The highest feeding intensity was recorded at night and during early morning hours. Euphausiids, mysids and a greater part of teleosts dominated night and morning diet, while decapods and cephalopods were most frequently in the daily and evening diet.Communicated by O. Kinne, Oldendorf/Luhe     

Interspecific comparisons of growth and diet among late larvae of three co-occurring clupeoid species in the Kii Channel,Japan

Growth and diet were compared among larvae of Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus and Pacific round herring Etrumeus teres. Compositions of prey items of the three species in the same month showed greater similarity than for the same species in different months. Prey size as well as prey taxa of the three species overlapped considerably with one another. Therefore, interspecific prey competition is likely in the case of limited food availability. The most abundant species tended to change from anchovy to round herring in early winter, from round herring to sardine in late winter and from sardine to anchovy in early spring, indicating a temporal segregation in use of the nursery grounds. Similar seasonal changes in growth rates were observed for the three species. Although interspecific prey competition is likely, the temporal segregation and similar temporal changes in growth rates could favor their coexistence.     

Influence of season on the feeding habits of the common sole Solea solea

The object of the study was to determine whether the composition of the diet of sole Solea solea Linnaeus, 1758 throughout the year is influenced only by the presence and abundance of prey or whether in addition it is influenced by a selection procedure resulting from its energetic and nutritional needs. Feeding habits were established by examining the stomach contents of males and females throughout the year. We recorded the presence or absence of each prey item and identified dominant, occasional and accidental prey. Differences in the seasonal composition of the basic diet were analysed (chisquare). Throughout the year, the diet consisted mainly of crustaceans, except in autumn when polychaetes were the most abundant prey. Significant differences (chisquare) in feeding habits were established between seasons and between sexes in each season. Some of the dominant prey (Ampeliscidae and Callianassidae) live exclusively in estuaries and bays, and occur in highest abundance during winter, the season in which sole enter estuaries to spawn. These prey items were present in higher numbers in the stomach contents of the sole during this period, reflecting the dependence of its diet on prey availability.     

Diets of deep-sea brachyuran crabs in the Western Mediterranean Sea

This study examines the feeding habits of Paromola cuvieri (Risso, 1816) and Geryon longipes A. Milne Edwards, 1881, the only two common deep-sea brachyuran crabs inhabiting the bathyal mud assemblages in the Catalan Sea (Western Mediterranean). Samples were obtained by bottom trawls at depths between 360 and 1871 m during 1983 to 1992. Both species had highly diverse diets, but very low feeding activity, as reflected by the high proportion of empty stomachs. Both characteristics may be important factors enabling deepsea crabs to adapt to bathyal zones, where trophic resources are scarce. The most important food items found in P. cuvieri were fish remains (teleost, sharks) and benthic decapods (Monodaeus couchii, Munida tenuimana). Scavenging activity plays an important role in this species. The diet of G. longipes included a broad range of benthic invertebrates. In the upper middle slope, the bivalve Abra longicallus, decapods (Calocaris macandreae and Monodaeus couchii), echinoderms and polychaetes were the dominant prey, with epibenthic peracarids as a secondary resource. On the lower middle slope, the incidence of decapod crustaceans (C. macandreae, Pontiphilus norvegicus) and peracarids in the diet declined. Small macrobenthic prey (glycerids, cumaceans or amphipods) were rare in the diet of both species, in accordance with the large size of the crab specimens studied. The absence of preferred prey items and the lack of food items of an optimum size on the lower slope may contribute to the progressive decline in abundance of P. cuvieri and G. longipes with increasing depth.     

Feeding habits of the Madeira rockfish <Emphasis Type="Italic">Scorpaena maderensis</Emphasis> from central Mediterranean Sea

In order to assess diet composition and niche breadth of this species, we analysed the stomach content of 182 specimens collected monthly along the eastern coast of Sicily (Central Mediterranean Sea). Overall, 50 prey taxa belonging to five major groups (algae, gastropods, crustaceans, polychaetes, fishes) were identified in 102 full stomachs. Benthic or epibenthic crustaceans, such as decapods, amphipods and isopods were the most important prey, whereas algae, gastropods, polychaetes and fishes were only occasionally ingested. In terms of composition by species, the diet of Scorpaena maderensis was characterized by a variety of rare or unimportant prey, which was consumed by few individuals only, although sometimes in large amount. As a result, S. maderensis can be considered a generalized and opportunistic feeder. The feeding intensity followed roughly a seasonal trend, with a minimum food intake in summer. The individual fish size was the most important factor affecting diet. According to the observed ontogenetic shift, small-sized individuals fed primarily on small crustaceans (i.e. amphipods and isopods), whereas large-sized specimens consumed preferably bigger and more vagile prey, such as walking and swimming decapods. No significant differences in diet were observed in relation to sex of predator and sampling season.     

Geographic and ontogenetic variation in the diet and daily ration of the bonnethead shark, <Emphasis Type="Italic">Sphyrna tiburo</Emphasis>, from the eastern Gulf of Mexico

To examine variation in diet and daily ration of the bonnethead shark, Sphyrna tiburo (Linnaeus 1758), animals were collected from three areas in the eastern Gulf of Mexico: northwest Florida (∼29°40′N, 85°13′W), Tampa Bay near Anclote Key (∼28°10′N, 82°42.5′W), and Florida Bay (∼24°50′N, 80°48′W) from March through September, 1998–2000. In each area, diet was assessed by life stage (young-of-the year, juveniles, and adults) and quantified using five indices: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), index of relative importance expressed on a percent basis (%IRI), and %IRI based on diet category (%IRI_DC). Diet could not be assessed for young-of-the-year in Tampa Bay or Florida Bay owing to low sample size. Diet analysis showed an ontogenetic shift in northwest Florida. Young-of-the-year stomachs from northwest Florida (n = 68, 1 empty) contained a mix of seagrass and crustaceans while juvenile stomachs (n = 82, 0 empty) contained a mix of crabs and seagrass and adult stomachs (n = 39, 1 empty) contained almost exclusively crabs. Crabs made up the majority of both juvenile and adult diet in Tampa Bay (n = 79, 2 empty, and n = 88, 1 empty, respectively). Juvenile stomachs from Florida Bay (n = 72, 0 empty) contained seagrass and a mix of crustaceans while adult stomachs contained more shrimp and cephalopods (n = 82, 3 empty). Diets in northwest Florida and Tampa Bay were similar. The diet in Florida Bay was different from those in the other two areas, consisting of fewer crabs and more cephalopods and lobsters. Plant material was found in large quantities in all stomachs examined from all locations (>15 %IRI_DC in 6 of the 7 life stage-area combinations, >30 %IRI_DC in 4 of the 7 combinations, and 62 %IRI_DC in young-of-the-year diet in northwest Florida). Using species- and area-specific inputs, a bioenergetic model was constructed to estimate daily ration. Models were constructed under two scenarios: assuming plant material was and was not part of the diet. Overall, daily ration was significantly different by sex, life stage, and region. The bioenergetic model predicted increasing daily ration with decreasing latitude and decreasing daily ration with ontogeny regardless of the inclusion or exclusion of plant material. These results provide evidence that bonnetheads continuously exposed to warmer temperatures have elevated metabolism and require additional energy consumption to maintain growth and reproduction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front,Scotia Sea

Samples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid's diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.     

Trophic strategies of euphausiids in a low-latitude ecosystem

Vertical distribution, diet, and morphology of adults were examined in 27 species of euphausiids occurring in the upper 1000 m in the eastern Gulf of Mexico. Vertical distribution patterns were similar to those found in the central ocean gyres and oceanic equatorial waters of the Atlantic, Indian and Pacific Oceans. Most species migrated vertically from their daytime depths of 300 to 600 m to the upper 300 m at night. Exceptions were the non-migrating species of Stylocheiron, which remained in the epipelagic zone day and night, and Nematobrachion boopis, which remained in the mesopelagic zone. Based on gut-contents analysis, the Gulf euphausiids were largely zooplanktivorous, with cyclopoid and calanoid copepods being the most common items in stomachs. ostracods were especially common in the stomachs of Thysanopoda spp. and phytoplankton in the guts of Euphausia spp. Nearly every species' diet contained a considerable amount of olive-colored debris, which may have been marine snow generated in the epipelagic zone. Cluster analysis grouped the euphausiids into nine diet guilds. Euphausiids with a generalized morphology (i.e., spherical eyes, uniform thoracic appendages) tended to group together and demonstrated little variety in stomach contents among species. Euphausiids with a specialized morphology (i.e., bilobed eyes, elongate thoracic appendages) showed considerable variety in stomach contents among species, and several species had diets that were highly specific. Many of the species that had similar gut contents fed on prey of different sizes, as indicated by the width of the calanoid copepod mandibles found in stomachs. Principal-components analysis of seven morphological characters yielded species groups that were similar, but not identical, to those generated by cluster analysis of stomach contents data. We inferred from this that morphological characters partly determine diet, but that behavior is also important. Using the 20 most abundant species and 3 niche parameters, we attempted to identify the degree of separation among euphausiids based on the level of overlap in vertical distribution and diet composition, and on differences in mean prey size. Overlap of <60% in vertical distribution or diet composition was considered to indicate distinction of that parameter. Of 190 total species pairs, only 4 pairs did not demonstrate niche separation in at least one of these categories. We found that differences in these niche parameters were greatest among species with a specialized morphology and least among species that were morphologically generalized.     

Fish and squid in the diet of king penguin chicks,Aptenodytes patagonicus,during winter at sub-antarctic Crozet Islands

The diet of king penguins, Aptenodytes patagonicus, rearing chicks was studied during three consecutive austral winters (1990, 1991 and 1992) at Crozet Islands. The mean stomach content mass of the 47 samples was 503 g. Percentages of wet and reconstituted masses showed that both fishes (66 and 36%, respectively) and squid (34 and 64%) are important components of the winter diet. Juveniles of the demersal onychoteuthid squid Moroteuthis ingens form the bulk of the cephalopod diet, and this was the main prey by reconstituted mass (57%). Myctophid fish (lantern-fishes) accounted for most of the fish diet, constituting together 32% by mass. The three main species of myctophids eaten in summer by king penguins were either very rare in winter (Electrona carlsbergi) or accounted for a smaller proportion of the diet (Krefftichthys anderssoni = 1.5% by mass and Protomyctophum tenisoni = 4.6%). Five other myctophids, which are rarely consumed in summer, contributed 24% of the diet by mass in winter (Gymnoscopelus piabilis = 18.1%, Lampichthys procerus = 2.4%, G. nicholsi = 1.3%, and Metelectrona ventralis and Electrona subaspera = 1.0%). The greater diversity of prey in winter suggests a more opportunistic feeding behaviour at a time probably marked by a change in prey availability. Both the known ecology of the fish and squid prey and the barely digested state of some items suggest that in winter breeding adults forage in the outer shelf, upper slope and oceanic areas in the close vicinity of the Crozet Islands to feed their chicks. Finally, using king penguins as biological samplers, the present work provides novel data on the previously unstudied mesopelagic/epibenthic marine community in waters surrounding the Crozet Islands. Seventeen myctophid fish have been identified to species level. These include several poorly known species in the southern Indian Ocean. The occurrence of small, nearly intact, cephalopods in the diet of king penguins suggests that spawning grounds of four squid species may be located near the Crozet Archipelago.     

Diet of the hatchetfish Sternoptyx diaphana

Sternoptyx diaphana Hermann is a non-migrating hatchetfish inhabiting the mesopelagic zone between 300 and 1500 m in temperate to tropical oceanic regions. An analysis is presented of the diet of this species, collected from 5 oceanic faunal provinces—the Pacific Subantarctic, and 4 subregions of the North Atlantic Ocean. Stomach analyses of 20 to 40 mm specimens revealed considerable intra-trawl (fish to fish), intraregional (Station to station), and inter-regional variation in size and composition of the diet. Generic composition of stomach contents differed noticeably from region to region, with the highest degree of faunal affinity being only 38%. The dominant food items both in terms of biomass and abundance also varied inter-regionally, with fish, euphausiids, or decapods predominant by weight; and euphaussids, copepods, or amphipods most prevalent by number. Differences in size distribution of food items from region to region were also noted. S. diaphana from regions of cooler overlying water masses fed on fewer but larger prey items, and diet was less diverse than that of fish from warmer waters. The diet consists primarily of omnivorous and carnivorous prey, and there is evidence that larger specimens feed on larger food items. The broad size-distribution and taxonomic spectrum of the prey, features of functional morphology, and low density as inferred from trawl catches, indicate that S. diaphana is a predator of limited pursuit capability. Feeding strategy appears to involve capture of the nearest available prey within its immediate vicinity.     

Biology of the deep-sea octopus Bathypolypus sponsalis (Cephalopoda: Octopodidae) from the western Mediterranean Sea

Several aspects of the biology of Bathypolypus sponsalis were studied from 297 individuals (115 males, 180 females and 2 indeterminates) caught in a depth range of 200–800 m depth in the western Mediterranean Sea. The paper presents data on sizes (length-weight relationships, size-frequency distributions) and reproduction (sex ratio, maturation, condition), and also analyses of the diet of B. sponsalis from samples taken throughout the year. Length-weight relationships showed that females are heavier than males at the same mantle length. Although mature individuals were found all year round, the maximum number occurred in spring and summer. Sexual maturation data revealed that males mature at smaller sizes than females. The gonadosomatic index increased with maturity in both sexes; the increase was gradual in males, but abrupt in females. The digestive gland index was used as a condition index and showed a differential behaviour with maturity; it increased gradually in females, but decreased in males. Like other octopus species, B. sponsalis appears to be an opportunistic predator, feeding on a great variety of preys. Stomach content analysis yielded a total of 19 different prey items belonging to four major groups (Crustacea, Mollusca, Ophiuroidea and Osteichthya). The first three groups were the more frequent preys, since crustaceans, molluscs and ophiuroids appeared in 76%, 49% and 30% of the stomachs, respectively. Decapoda Reptantia (among crustaceans) and cephalopods and bivalves (among molluscs) constituted the more abundant prey items. While the Decapoda Reptantia group was significantly more abundant in stomach contents of females, gastropods were taken more frequently by males. These differences in diet could reveal females as a more active predators than males. Received: 5 March 2000 / Accepted: 7 November 2000     

Transport of brine shrimps via the digestive system of migratory waders: dispersal probabilities depend on diet and season

Waterbirds are known to disperse invertebrate propagules that survive gut passage, but there is very little information about how the probability of dispersal changes at different times of the annual cycle when birds move in different directions, or how it is affected by changes in diet. We studied internal transport of brine shrimp Artemia cysts by migratory waders in the Odiel saltworks in south-west Spain. Viable cysts of parthenogenetic Artemia were abundant in the faeces and regurgitated pellets of redshank Tringa totanus, pellets of spotted redshank T. erythropus, and faeces of black-tailed godwit Limosa limosa during spring and/or autumn migrations in 2001–2002, but were not recorded during winter. Godwits did not produce pellets, and spotted redshank faeces were not sampled. Significant correlations between the number of cysts in a pellet or faecal sample and the proportion of that sample constituted by Artemia adults suggested that most cysts were ingested while in the ovisacs of gravid females. The proportion of cysts destroyed during digestion increased when accompanied by harder food items or grit, and when fewer cysts were ingested. The median number of intact cysts was higher in redshank faeces than in their pellets, but cysts extracted from pellets were more likely to hatch. A higher proportion of redshank pellets contained Artemia cysts in spring than in autumn, but more redshank migrated through the area in autumn. Significantly fewer cysts were recorded in redshank pellets in winter than in spring or autumn. Our results confirm that there is potential for long-distance dispersal of Artemia cysts via waders during both northwards (spring) and southwards (autumn) migrations.     

Spatio-temporal variations in the diet and stable isotope composition of the Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 of the continental shelf of southeastern Brazil

The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m). The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio. δ¹⁵N and δ¹³C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7 for M. hubbsi was estimated using δ¹⁵N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels.     

Feeding ecology of Liocarcinus depurator (Decapoda: Portunidae) in the Ria de Arousa (Galicia,north-west Spain): effects of habitat,season and life history

The diet of the portunid crab Liocarcinus depurator (L.) in soft-bottom areas of the Ría de Arousa (Galicia, north-west Spain) was studied by analysis of stomach contents, and by comparison of habitats of contrasting abundance, composition and diversity of prey communities. Monthly samples were taken from July 1989 to June 1990 (N=3747) in mussel (Mytilus galloprovincialis) raft-culture areas and central channel zones. Ninety-two food items were identified: crustaceans, molluscs, polychaetes, ophiuroids and fishes were the dominant prey. The raft epifauna and the mussels constituted the dominant group of prey in the raft areas and inner channel station (the epifaunal crab Pisidia longicornis comprised 30 to 52% of the diet), whereas the benthic macroinfauna was the dominant food component in the mid-outer channel (polychaetes constituted 32% of the diet). In the epifaunal community, diet selection for P. longicornis was positive and for amphipods was negative, whereas within the infauna diet selection for bivalves and ophiuroids was positive and for polychaetes negative or neutral. The seasonal importance of P. longicornis and M. galloprovincialis varied in the diet of L. depurator parallel to seasonal activities connected with mussel culture (seeding, thinning, harvesting) that determine the availability of prey from the rafts. Major changes in the composition of the diet related to the life history of L. depurator occurred during ontogeny. In the raft zones, consumption of mussels and fishes increased with increasing body size, while the consumption of Natantia, non-decapod crustaceans, gastropods, polychaetes Pectinariidae and plants decreased with increasing crab size. Maximum consumption of P. longicornis was by L. depurator individuals of intermediate size (15 to 44 mm carapace width). Stomach fullness (measured as dry weight of food) increased with increasing body size, but with negative allometry. During the late pre-moult and early post-moult periods L. depurator did not consume any food; maximum stomach fullness was recorded for the late post-moult and intermoult stages. Female food consumption decreased during egg incubation. Food consumption was greater in autumn and winter than at other seasons; this appears to be related to seasonal changes in reproduction and moulting.     

Dietary constraints on reproductive periodicity in two sympatric deep-sea astropectinid seastars

Examination of the diet of two sympatric species of seastar, Bathybiaster vexillifer and Plutonaster bifrons from 2200 m depth in the Rockall Trough, NE Atlantic Ocean (57°18'N; 10°28'W), suggested that diet may determine the different reproductive patterns found between these two species. In the non-seasonally breeding B. vexillifier, the diet showed a high Shannon-Wiener prey diversity index, the dominant prey being the irregular echinoid Hemiaster expergitus together with a variety of prosobranch gastropods and protobranch bivalves. By contrast, the prey diversity in the seasonally breeding P. bifrons was significantly lower than that of B. vexillifer. In addition, organic carbon content in the sediment residue in the stomachs of P. bifrons displayed a seasonal cycle, while no such seasonality was detected in B. vexillifer. The stomachs of P. bifrons also contained a higher proportion of scavenged material, including the seasonally available remains of mesopelagic blue whiting. These data, together with Bathysnap (time-lapse camera) observations of feeding behaviour in both species, suggest that B. vexillifer is a predator feeding deep in the sediment, whereas P. bifrons feeds close to the sediment surface where it is affected by the seasonal availability of phytodetritus and fish carcasses.     

Measurement of copepod predation on nauplii using qPCR of the cytochrome oxidase I gene

A method to directly measure predation rates by older stage copepods upon copepod nauplii using species-specific primers for the mitochondrial cytochrome oxidase subunit one gene (mtCOI) and real-time quantitative PCR (qPCR) was developed. The general approach is to determine the mtCOI gene copy number of an individual prey organism and the copy number of the same gene in the stomachs of predatory copepods collected in the field. From the knowledge of DNA disappearance rates in the stomachs, ingestion rates can be calculated. In October 2006, laboratory experiments were carried out with Acartia tonsa N1 and N2 as prey and adult female Centropages typicus as predator. The copepods were collected in Narragansett Bay, USA. A. tonsa mtCOI copy numbers copepod⁻¹ were determined for stages N1–C1 and for adults. A. tonsa DNA was detectable in the guts of the predators for as long as 3 h. Exponential rates of decline in prey DNA from the stomachs of the predators are similar to those measured for gut pigments. Because of the very small amount of DNA in an individual N1 or N2 nauplius, procedures were developed to maximize the quantitative extraction and recovery of DNA and to increase the sensitivity of the method. Two quite divergent haplotypes of A. tonsa were found in Narragansett Bay, which required separate qPCR primers; one was present in summer (July) and the other in fall and winter (October and February). With modification, the methods in this study can likely be applied to a range of predator–prey systems.     

Natural feeding activity of the crab Callinectes ornatus (Portunidae) in Ubatuba Bay (São Paulo, Brazil): influence of season, sex, size and molt stage

The natural diet of Callinectes ornatus in Ubatuba Bay, Ubatuba (SP), Brazil, was studied. Influence of season, sex, size and molt stage variation in the diet were also described. Specimens were collected monthly over a period of 1 year, in Ubatuba Bay, using a fishing boat equipped with a double rigged net. The relative degree of stomach fullness, frequency of occurrence, and quantitative scoring (percentage) were determined. Digested material, crustaceans, sediment and mollusks were the principal items of the diet. Echinoderms, annelids, plants, and fishes were also notable prey items, and other food categories (foraminiferans, cnidarians, worms and bryozoans) occurred in low percentages. A non-significant difference was found in many items during seasonal analysis, i.e. plants, foraminiferans, cnidarians, bryozoans and digested material were present at highest percentages during summer and autumn, while crustaceans and echinoderms were consumed in larger amounts during the spring and winter. Males and females consumed a similar diet, although ovigerous females showed a greater tendency to feed on items with soft tissues (fish, squid, shrimp). Juveniles fed more on sedentary and calcareous items than did adults, showing a significant tendency to reduce consumption of foraminiferans, annelids, bryozoans, echinoderms and sediment as the animal increased in size, accompanied by an elevation in the consumption of plants, crustaceans and fish. These crabs are opportunistic predators with a preference for crustaceans and mollusks that is correlated with the availability of prey and the ontogenetic phase of the predator. Received: 21 January 2000 / Accepted: 2 October 2000     

Diet of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> in False Bay,South Africa

The diet of Octopus vulgaris was analysed using instantaneous daytime observations, midden counts, and stomach contents and a total of 39 prey species were identified. From stomach contents, the most important prey species were Plagusia chabrus (64.6% IRI, index of relative importance) and Haliotis midae (21.6% IRI). Crustaceans were the most frequently found prey group in octopus stomachs (63.6% frequency of occurrence), followed by molluscs (37.6%), teleosts (11.2%), and polychaetes (10.8%). Prey size and diversity increased with increasing octopus size. From middens, the mean shell lengths of H. midae consumed by small, medium, and large O. vulgaris were 53.3, 72.6, and 86.0 mm, respectively. Compared with stomach contents, midden counts were 3 times higher for shelled molluscs, but 5 times lower for crustaceans and soft-bodied organisms. Similarly, instantaneous daytime observations were 3 times higher for shelled molluscs, but 5 times lower for crustaceans and 2 times lower for soft-bodied organisms.Communicated by G.F. Humphrey, Sydney     

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.