Dissolved organic carbon (DOC) is essential to balance the metabolic demands of four dominant North-Atlantic deepsea sponges

Abstract

Sponges are ubiquitous components of various deep-sea habitats, including cold water coral reefs and deep-sea sponge grounds. Despite being surrounded by oligotrophic waters, these ecosystems are known to be hotspots of biodiversity and carbon cycling. To assess the role of sponges in the carbon cycling of deep-sea ecosystems, we studied the energy budgets of six dominant deep-sea sponges (the hexactinellid species Vazella pourtalesi, and demosponge species Geodia barretti, Geodia atlantica, Craniella zetlandica, Hymedesmia paupertas and Acantheurypon spinispinosum) in an ex situ aquarium setup. Additionally, we determined morphological metrics for all species (volume, dry weight (DW), wet weight (WW), carbon (C) content, and ash-free dry weight (AFDW)) and provide species-specific conversion factors. Oxygen (O2) removal rates averaged 3.3 {+/-} 2.8 {micro}mol O2 DWsponge h-1 (all values mean {+/-} SD), live particulate (bacterial and phytoplankton) organic carbon (LPOC) removal rates averaged 0.30 {+/-} 0.39 {micro}mol C DWsponge h-1 and dissolved organic carbon (DOC) removal rates averaged 18.70 {+/-} 25.02 {micro}mol C DWsponge h-1. Carbon mass balances were calculated for four species (V. pourtalesi, G. barretti, G. atlantica and H. paupertas) and revealed that the sponges acquired 1.3-6.6 times the amount of carbon needed to sustain their minimal respiratory demands. These results indicate that irrespective of taxonomic class, growth form, and abundance of microbial symbionts, DOC is responsible for over 90 % of the total net organic carbon removal of deep-sea sponges and allows them to sustain in otherwise food-limited environments on the ocean floor.