Cold-water coral reefs and adjacent sponge grounds: hotspots of benthic respiration and organic carbon cycling in the deep sea

Cécile Cathalot,Marc Lavaleye,Gerard Duineveld,Tom J S Cox,Dick Van Oevelen,Filip J R Meysman,Tina Kutti

doi:10.3389/fmars.2015.00037

Abstract

Cold-water coral reefs and adjacent sponge grounds are distributed widely in the deep ocean, where only a small fraction of the surface productivity reaches the seafloor as detritus. It remains elusive how these hotspots of biodiversity can thrive in such a food-limited environment, as data on energy flow and organic carbon utilization are critically lacking. Here we report in situ community respiration rates for cold-water coral and sponge ecosystems obtained by the non-invasive aquatic Eddy Correlation technique. Oxygen uptake rates over coral reefs and adjacent sponge grounds in the Traena Coral Field (Norway) were 9-20 times higher than those of the surrounding soft sediments. These high respiration rates indicate strong organic matter consumption, and hence suggest a local focusing onto these ecosystems of the downward flux of organic matter that is exported from the surface ocean. Overall, our results show that coral reefs and adjacent sponge grounds are hotspots of carbon processing in the food-limited deep ocean, and that these deep-sea ecosystems play a more prominent role in marine biogeochemical cycles than previously recognized.

Highlights

Cold-water corals and sponges form complex reef structures on the seafloor (Figure 1), which support a rich community of suspension-feeding fauna and play a crucial role as a refuge, feeding ground and nursery for various commercial fishes (Miller et al, 2012)
Upscaling our Aquatic Eddy Correlation (AqEC) measurements to the whole reef structure provided an average Community Respiration (CR) rate of 122 ± 10 mmol O2 m−2 d−1 (Table 5), whereas upscaled bottom-up CR rates gave a value of 43 ± 7 mmol O2 m−2 d−1
Despite the complex topography of the reef structure and the substantial uncertainty associated with the “bottom-up” CR rates, the AqEC and bottom-up values align very well, and are not significantly different for the sponge ground and bare sediment

Summary

Introduction

Cold-water corals and sponges form complex reef structures on the seafloor (Figure 1), which support a rich community of suspension-feeding fauna and play a crucial role as a refuge, feeding ground and nursery for various commercial fishes (Miller et al, 2012). These reef ecosystems are widespread across the deep ocean (Klitgaard and Tendal, 2004; Roberts et al, 2006), but they face an uncertain future, as the human imprint on the deep-sea rapidly increases (Pusceddu et al, 2014). Data on the energy flow and organic carbon (OC) processing rates within these deep-sea ecosystems are critically needed

Methods

Results

Conclusion