Distribution of Digestive Enzymes in Zooplankton during the Spring Bloom in a Nova Scotia Inlet

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Abstract
Nonparametric correlation and principal component analysis were used to examine relations between digestive enzyme activity in zooplankton and qualitative and quantitative measures of particulate organic matter and between enzymes and composition of the zooplankton community. Barnacle nauplii in near-surface (5 m) water during the first part of the bloom caused heterogeneity, which confounded relationships between enzyme activity and potential substrate concentration. Lack of coherence among enzymes in the 5 m zooplankton was also observed. The less variable deepwater community showed intercorrelation among the enzymes measured. At 30 m, enzyme concentrations in Pseudocalanus were correlated with concentration of particles less than 20 μm, which were dominant in the first part of the bloom. Two time-related events significantly affected zooplankton enzyme levels: one was clearly related to the period of dominance of barnacle larvae and the other with an increase in the C:N ratio from around 5 to greater than 7 in midbloom coinciding with a shift in phytoplankton from smaller forms of apparently higher protein content to large colonial diatoms. The results generally support the hypothesis that the amount and chemical composition of food supply can affect zooplankton digestive enzymes, but they also demonstrate the problems of interpretation if community structure is not well defined and spatial and temporal distribution of organisms not carefully circumscribed.