Rate of chitobiase degradation as a measure of development rate in planktonic Crustacea

We have developed a method to determine development time (molt rate) in bot h single and mixed populations of crustacean zooplankton based on turnover of the chitinolytic enzyme chitobiase in the ambient medium. We examined th e relationship between body size and chitobiase activity released into the medium following molt in three freshwater cladoceran species, Ceriodaphnia spp., Daphnia pulex, and Daphnia magna. Chitobiase activity increased with body length, and a common relationship was observed among all three species (r(2) = 0.82, p < 0.0001). Under steady-state conditions in laboratory cul tures, the rate of decay of this enzyme in the medium was balanced by its r ate of production by molting animals. The rate of decay of the enzyme in th e absence of animals was therefore also its rate of production, which is a measure of the average rate of development of the crustacean zooplankton co mmunity. Development times for a D. magna culture (2x) and a Ceriodaphnia s pp. - D. magna mixed culture were 65.4 vs. 62 h, 59 vs. 67 h, and 46.6 vs. 50 h, respectively, as measured by this "chitobiase method" versus conventi onal molt rate determinations.