Evaluation of chitobiase-based estimates of biomass and production rates for developing freshwater crustacean zooplankton communities

Increasing attention has been devoted to the development of alternative (often bio-chemical) methods for measuring crustacean zooplankton productivity because conventional methods are not globally applicable and rarely practical when community-level rates are required. Here we evaluate the chitobiase method as a rapid, routine and instantaneous method for measuring the productivity of fresh-water crustacean zooplankton communities. Chitobiase, a moulting enzyme, is liberated into water following moulting and production rates are calculated by measuring its turnover rate in the water column. First, using literature-based instar- and stage-specific individual body mass values, we found a common relationship between post-moult body size (and individual chitobiase activity) and the biomass produced between successive moults for common freshwater groups. Secondly, using a time-series of weekly measurements in a North-Temperate lake, we found a good correspondence between the standing activity of chitobiase in the water column (CBA(NAT)) and the biomass sampled by a plankton net and laser optical plankton counter (LOPC). Overall, however, CBA(NAT)-based biomass more closely corresponded to LOPC-based biomass estimates. Lastly, depth-specific biomass production rates and daily production to biomass estimates varied positively with temperature. Daily production to biomass ratios also varied closely with predictions of a taxon-specific temperature-dependent model for freshwater zooplankton.