Trophic ecology of seven Antarctic gorgonians through stable isotope analysis and biochemical balance

Abstract

A large part of Antarctic shelf communities consist of sessile suspension feeders, which play a key role in the biogeochemical cycles and are linked to the pelagic productivity. Gorgonians are the second most dominant macrobenthic taxon in abundance in the Weddell Sea, but there have been very few studies on their basic ecology including its trophic ecology. Studies of food web structure are complex but stable isotope analysis and the biochemical levels (i.e. lipid-protein-carbohydrate balance) may give some cues of its role in the benthic-pelagic coupling processes and its trophic strategies. The trophic ecology of seven gorgonian species (Primnoisis sp, Faniella nodosa, Ainigmapdilon antarcticus, Notisis sp, Primnoella sp, Dasystinella sp and Thouarella sp) in two contrasting areas (Antarctic Peninsula and Eastern Weddell Sea) in autumn conditions was studied to understand the energetic guilds linked to the feeding and energy storage, which may be part of the explanation of the reproductive traits of these gorgonians. All the seven species showed a small range in δ13C values, from about -27.7‰ to -24.8‰. The range in δ15N was slightly larger, from 4.1‰ to 7.5‰. The lower average of protein was 158.7 ± 76.9 μgProteins mg-1OM, and the higher, 556.3 ± 78.6 μgP mg-1OM. The carbohydrate average ranged from 10.5 ± 3.4 μgCarbohydrates mg-1OM to 80.7 ± 28.7 μgC mg-1OM, and the lipid values ranged from 105.1 ± 99 μgLipids mg-1OM to 776.4 ± 354.1 μgL mg-1OM. The results of the stable isotope data of the seven gorgonians fit very well with phytodetritus found in green carpets in autumn and is in line with previous one in polar or deep sea areas. This means that an important part of the diet is based on sinking or resuspended material, which confirms the previous hypothesis that part of the suspension feeders survive because of the fuelling through this phytoplankton material. Whilst stable isotope analysis indicates similar feeding strategies in these seven gorgonian species, the biochemical balance indicates a very different energy storage and metabolism strategies among species. Lipids reflect the capability of a species to integrate environmental constraints even in very short distances. It has been shown that in autumn, potentially resuspendable sediments may be different in the lipid contents (food availability in form of senescent or died phytoplankton) in the eastern Weddell Sea