Metabolism and chemical composition of zooplankton and hyperbenthos from the Great Barrier Reef waters, North Queensland, Australia

Abstract

Rates of oxygen consumption (R) and ammonia excretion (E) of a total of 22 species of zooplankton and hyperbenthos, which weighed 0.0012 to 26.7 mg dry mass (DM), from inshore and slope waters of the Great Barrier Reef were determined at in situ temperatures (23 to 30°C). Rs ranged from 0.0048 to 118.3 μL O₂ ind.⁻¹ h⁻¹ and Es from 0.00051 to 15.9 μg NH₄-N ind.⁻¹ h⁻¹. Stepwise regression analyses in which the differences in body mass are taken into account revealed that zooplankton and hyperbenthos exhibited comparable R, but the latter showed lower E than the former. As a result, the atomic ratio of R to E (O : N) of hyperbenthos (geometric mean: 53.1) was greater than that (16.4) of zooplankton. No appreciable differences were evident in C and N composition of the bodies between zooplankton-hyperbenthos; total carbon (C) ranged from 18.0 to 47.2% of DM and total nitrogen (N) from 2.4 to 12.7% of DM, with C : N ratios of 3.1–7.5. Judging from C and N composition, protein was the major component of body organic matter of both zooplankton and hyperbenthos. In terms of N-specific R and N, the present zooplankton data are comparable to those published on tropical zooplankton and small fishes with similar body N. Compared with zooplankton, lower specific Es and higher O : N ratios of hyperbenthos were interpreted to reflect their partial or entire dependence on diets characterized by lower N composition (detritus).