Abundance, oxygen consumption and carbon demand of brittle stars in Young Sound and the NE Greenland shelf

We used sea floor photography to estimate brittle star abundance in Young Sound, NE Greenland and the adjacent shelf. From photos covering a total area of 78 m2 and spanning a depth range from 20 to 310 m we found maximum average densities of >400 ind. m–2 at 40 to 80 m depth. Ophiocten sericeum was the dominant species. However, gradual changes in species and size composition with depth were observed. Average biomass was ~600 mg C m–2 with highest values at sites dominated by the large Ophiopleura borealis (up to 2190 mg C m–2). We measured average individual oxygen consumption of 3 dominant species at ambient temperature (–1.0°C) and salinity in incubation chambers using a fiber-optic oxygen sensor enabling continuous measurements. We established a general relation between individual disc diameter (D, mm) and oxygen consumption (R, μmol O2 h–1 ind.–1): R = 6.0 × 10–4 × D2.60 (R2 = 0.96, n = 33), which facilitated the estimation of community respiration and carbon demand from sea floor images. Peaks in total carbon demand were found in the fjord at 30 m (14 mg C m–2 d–1) and 160 m depth (13 mg C m–2 d–1), resulting from high densities of medium sized (10 to 15 mm disc diameter) O. sericeum, and the presence of the very large (20 to 35 mm disc diameter) O. borealis, respectively. At the other stations values ranged from 0.5 to 8 mg C m–2 d–1. Overall, our results demonstrate that brittle stars, despite very low individual energy requirements, contribute significantly to marine carbon cycling in Young Sound as well as in the shelf areas off NE Greenland.