Role of echinoderms in benthic remineralization in the Chukchi Sea

Abstract.

The role of large, epibenthic organisms in carbon cycling at high latitudes is difficult to assess using standard ship-board collection techniques. We used a remotely operated vehicle equipped with video imaging to examine the distribution and abundance of epibenthic organisms in the northeast Chukchi Sea during June 1998. At each of 11 sites, we collected between 25 and 50 images from a minimum of 20 min of video. We observed 15 different epibenthic taxa, with the echinoderms (Ophiura sarsia, O. maculata, Ophiopholis aculeata, Stegophiura nodosa, and Echinarachinus parma) overwhelmingly dominating the epibenthos. Echinoderm density was highly variable, ranging from 0.2 to 256.6 individuals m^–2 (median=16.3), and echinoderm biomass varied between <0.5 and 4,988 mg C m^–2 (median=737). The highest biomass of ophiuroids recorded (3,388 mg C m^–2) is 30% higher than the highest previously reported from an Arctic shelf. Using a relationship between biomass and respiration developed for deep-sea organisms living at cold temperatures, we estimated respiration rates from <0.1 to 15.0 mg C m^–2 day^–1 (median=1.9). Respiration rates measured on board were several orders of magnitude higher than those obtained from the predictive equation. Further work is needed to assess echinoderm respiration rates accurately under in situ conditions. Even with calculated minimal values for respiration rates, a comparison of epifaunal and infaunal respiration at four stations revealed that echinoderm respiration accounted for as much as 25% of total respiration. High epifaunal respiration rates and biomass values are likely supported by high concentrations of particulate organic carbon carried by Bering Sea water flowing through the eastern Chukchi Sea. Our observations support observations from the Eurasian Arctic that echinoderms dominate the epibenthos of Arctic shelves and that the role of these organisms in carbon remineralization must be considered if we are to generate accurate models of carbon cycling in the Arctic.