Maerozooplankton of a deep sea hydrothermal vent: In situ rates of oxygen consumption1

Abstract

Oxygen consumption rates of mixed macrozooplankton from the vicinity of a deep sea hydrothermal vent system were measured with a three‐chambered slurp‐gun respirometer manipulated by the submersible Alvin at one vent station, clam acres (2,615‐m depth), on the axis of the East Pacific Rise at 21°N. Diffuse warm‐water effluents (≤25°C) along crevices between pillow lava formations were densely populated with epibenthic megafauna. In sharp contrast, the surrounding nonvent area had similar physical features but few visible fauna. Four plankton collections were made in the vent area and two in the nonvent area on two separate dives. Vent and nonvent plankton were dominated, numerically and gravimetrically, by a calanoid copepod, Isaacsicalanus paucisetus. Abundance and biomass of the mixed plankton were highest over the vent area and decreased by as much as two orders of magnitude over the nonvent area. Although weight‐specific oxygen consumption rates of plankton from the vent and nonvent areas, measured at the same ambient temperature (1.6°C) were of similar magnitude (1.68–4.26 µl O2 mg−1 dry wt d−1), both were one to two orders of magnitude lower than published rates for surface‐water mixed plankton. Oxygen consumption rates per cubic meter ranged from 564.5 µl O2 m−3 d−1 at one vent site to 4.3 over the nonvent area. Vent and nonvent rates of oxygen consumption per cubic meter fall within the range of values previously measured for mixed macrozooplankton from surface waters to bathypelagic depths.