Food web functioning of the benthopelagic community in a deep-sea seamount based on diet and stable isotope analyses

Abstract

Trophic interactions in the deep-sea fish community of the seamount Galicia Bank (NE Atlantic) was inferred by using stomach contents (SC) and stable isotope analyses (SIA) of 26 fish species and their main prey. Samples were collected during three cruises performed in summers’ 2009, 2010 and 2011 between 625 and 1800 m depth. Three main trophic guilds were determined using SC data: pelagic feeders, benthopelagic-feeders and benthic-feeders. Low degree of overlap (both in habitat and diet) was detected for most of species. However, high competition was observed among the benthopelagic feeders Etmopterus spinax, Hoplostethus mediterraneus and Epigonus telescopus, and the benthic feeders Lepidion eques and Nezumia aequalis.

A high correlation was found between δ15N and δ13C (r =0.74, p< 0.05) for the whole species analysed. When calculating trophic levels (TLs) for the main fish species by using SC and SIA some discrepancies arose, probably attributed to the sampling period (summer). TLs calculated from SIA analyses were significantly higher than that obtained from SC only in the benthic-feeders trophic guild, maybe indicating an enrichment-impoverishment trend in benthic communities during previous months. It appears that, during summer, functioning of food webs in Galicia Bank are more influenced by the communities dwelling the water column than by deep-sea benthos. Vertical migrating benthopelagic shrimps and macrozooplankton, mainly euphausiids and mysids, were identified to play a key role in the Galicia Bank food webs, unlike benthic fauna which was found as a pauperized compartment. These results demonstrate the importance of both approaches, SC (snapshot of diet) and SIA (assimilated food in previous months), giving an overview of food web dynamic in different compartments of the ecosystem.