Yves Scailteur

Trophic diversity within the eastern Weddell Sea amphipod community

Amphipod crustaceans form one of the most diversified animal groups within the Antarctic macrozoobenthos, both from the taxonomic point of view (more than 800 species have been recorded in the Southern Ocean) as by niche occupation and at the community level. Thus, amphipods are likely to play an important role in the organic matter fluxes that occur on the Antarctic sea floor. The dietary behaviour of these peracarids is still poorly known, and only few species have been analysed. This paper describes the trophic preferences of some dominant amphipod species of the Eastern Weddell Sea benthos, deduced from stomach content analyses and behavioural observations in aquaria. More than 1000 specimens, belonging to 40 species (representing 27 genera and 15 families) were dissected; and several thousands of individuals were kept in aquaria for 6–9 weeks and presented with various potential foods. These two approaches revealed at least eight different feeding types: suspension-feeding, deposit-feeding, deposit-feeding coupled with predation, opportunistic predation, micropredatory browsing, macropredation coupled with scavenging, opportunistic necrophagy and true necrophagy. These different behaviours cover almost all the possible feeding types with the exception of macroherbivorous browsing. Among the eight described feeding types, no particular one is dominant. In the same way, types involving microphagy and macrophagy are equally represented. Predatory types (opportunistic or exclusive) account for 64% of the species analysed, while scavenging types (facultative or obligate) account for 60%. The overlap suggests that many amphipod species have a wide dietary spectrum and are able to take advantage of different food resources.

Combined lipid, fatty acid and digestive tract content analyses: a penetrating approach to estimate feeding modes of Antarctic amphipods

Abstract. Antarctic amphipods from the Weddell Sea and Bransfield Strait were collected to investigate the impact of various species and feeding types on lipid and fatty acid compositions. In combination with digestive tract content analyses, such information can help clarify the type of feeding mode of the various amphipod species. Micro- and macropredatory amphipod species had only small amounts of triacylglycerols as storage lipids, whereas the deposit-feeder Epimeria georgiana was rich in triacylglycerols (55% of total lipids). The fatty acids 22:6(n-3), 20:5(n-3), 18:1(n-9) and 16:0 were major lipid components of most species. Ampelisca richardsoni, a suspension feeder, had a high amount of 18:4(n-3), a major component of cryptophytes and/or haptophytes, connected with feeding on sedimenting phytoplanktonic material and with a strong bentho-pelagic coupling. In Oradarea edentata, fragments of brown algae were found almost exclusively. The major fatty acid of the macroalgae, 20:4(n-6), replaced the 22:6(n-3) in the phospholipids and triacylglycerols of the amphipod. The sponge eater, Echiniphimedia hodgsoni, was rich in 16:1(n-7) and 18:1(n-7), suggesting that the unidentifiable organic matter was of diatom origin. Eusirus perdentatus, a typical predator, had high proportions of saturated and monounsaturated fatty acids, showing no specialisation in lipid and fatty acid composition. The fatty acid composition of Epimeria georgiana was similar to that of Eusirus perdentatus. However, high levels of triacylglycerols in Epimeria georgiana reflect periodical food plenty and starvation, due to its dependence on dead items. The fatty acid composition of the necrophage Waldeckia obesa was clearly different because of the predominance of 18:1(n-9) (>40% of total fatty acids). This dominance is probably the result of feeding on highly degraded carrion-derived organic matter, which is the major food of W. obesa.

Diversity of epibenthic habitats of gammaridean amphipods in the eastern Weddell Sea

Gammaridean amphipods appear ubiquitous in the shelf communities of the eastern Weddell Sea where more than 230 species have been recorded. Comparison of catches of the 40 most common species taken by different gears and ethological observations in the aquarium allowed us to distinguish 6 groups: endobenthic, epibenthic, hyperbenthic (or suprabenthic), benthopelagic, pelagic and cryopelagic. Only epibenthic species, which form the bulk of the fauna, are dealtwith in the present paper. Aquarium observations indicated three different epibenthic strata occupied by amphipods: the sediment surface, and a lower and upper level on the substrata formed by sessile suspension feeders. In addition, four symbiotic microhabitats were detected in or on sponges, ascidians, hydrozoans and gorgonians.