Sponges are ubiquitous components of various deep-sea habitats, including cold water coral reefs, and form deep-sea sponge grounds. Although the deep sea is generally considered to be a food-limited environment, 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 carbon budgets of six dominant deep-sea sponges of different phylogenetic origin, with various growth forms and hosting distinct associated microbial communities, in an ex situ aquarium setup. Additionally, we determined biomass metrics-planar surface area, volume, wet weight, dry weight (DW), ash-free dry weight, and organic carbon (C) content-and conversion factors for all species. Oxygen (O 2) removal rates averaged 3.3 ± 2.8 μmol O 2 g DW sponge h −1 (mean ± SD), live particulate (bacterio-and phytoplankton) organic carbon removal rates averaged 0.30 ± 0.39 μmol C g DW sponge h −1 and dissolved organic carbon (DOC) removal rates averaged 18.70 ± 25.02 μmol C g DW sponge h −1. Carbon mass balances were calculated for four species 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 themselves in otherwise food-limited environments on the ocean floor.

Little information exists on the environmental requirements of sponges from the Canadian Arctic, increasing the necessity to establish baseline distribution data on sponge assemblages to predict their susceptibility to climate change. Here we describe the sponge taxa of Hudson Strait, Ungava Bay, Western Davis Strait and Western Baffin Bay collected by Canadian research vessel trawl surveys. A total of 2026 sponge specimens were examined, and 93 different taxa were identified with 79% identified to species, of which 2 are new to science, 1 recorded for the first time in the North Atlantic, 16 are new records for the northwest Atlantic, and 10 are new records for the Baffin Bay, Davis Strait and Hudson Strait sponge fauna. Taxonomic distinctness was higher north of Cape Dyer and south of Davis Strait, whereas the number of species reached a maximum in Davis Strait, which represents the southern distribution limit of the arctic sponge fauna along the slope in this region. Five sponge species assemblages were identified, some of which have been observed elsewhere, suggesting that they may be common to the North Atlantic and at the generic level to the global oceans. Two of the Baffin Bay−Davis Strait assemblages were characterized by large structure-forming astrophorids: one, with arctic species, found at midwater depths in Baffin Bay and the other, characterized by boreal species, was found deeper, south of Davis Strait. Another assemblage characterized by glass and carnivorous sponges was found along the continental slope of western Baffin Bay. Candidate target indicator species are provided for future sponge community monitoring.

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 µmol O2 DWsponge h−1 (all values mean ± SD), live particulate (bacterial and phytoplankton) organic carbon (LPOC) removal rates averaged 0.30 ± 0.39 µmol C DWsponge h−1 and dissolved organic carbon (DOC) removal rates averaged 18.70 ± 25.02 µmol 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.