Trophic structure and chemosynthesis contributions to heterotrophic fauna inhabiting an abyssal whale carcass

Abstract

The trophic structure and role of chemosynthesis remain unexplored in deep-sea whale-fall communities in areas other than the California margin. This gap limits the understanding of these communities and their ecological relationships with other chemosynthetic ecosystems, such as vents and seeps. Here, we studied 3 different whale skeleton microhabitats with hypothesized high, intermediate and low reducing conditions as well as the sediments surrounding an abyssal whale fall (4204 m depth, SW Atlantic Ocean). We analyzed trophic structures (δ13C and δ15N) and the contribution of chemosynthetically derived carbon to heterotrophic species. The high and intermediate reducing microhabitats harbored food webs dominated by consumers of chemosynthetic production, similar to those of diffusive areas of hydrothermal vents and seeps. Both the low reducing microhabitat and the sediments harbored food webs with greater trophic complexity, dominated by higher consumers mainly relying on whale and/or photosynthesis-derived organic matter, a type of food web commonly reported in small whale, wood and kelp falls. The main whale-fall ecosystem engineer, the bone-eating worm Osedax, appeared to produce unique food web effects not observed in other chemosynthetic habitats. We conclude that whale falls provide the deep sea with a mosaic of microhabitats that supports assemblages with different chemosynthesis reliance levels and trophic structures, similar to those found at vents and seeps. Such a mosaic allows species-rich communities with numerous trophic levels to develop in a very small area of the food-limited deep sea.