Comparison of mesozooplankton production estimates from Saanich Inlet (British Columbia, Canada) using the chitobiase and biomass size spectra approaches

Abstract

Zooplankton production estimates are necessary to understand the availability and transfer of energy to higher trophic levels in marine food webs. Methods have been developed to quantify zooplankton production; however, they are difficult to compare as they focus on single species, groups, stages, or size classes of zooplankton. We compared 2 methods for estimating crustacean production: the chitobiase method (based on a crustacean moulting enzyme), and 3 empirical growth rate models (Huntley-Lopez, Hirst-Lampitt, and Hirst-Bunker) applied to optically resolved mesozooplankton normalized biomass size spectra (NBSS). Mesozooplankton net samples were collected between March and August of 2010 and 2011 in Saanich Inlet (British Columbia, Canada) and analyzed in the laboratory using microscopy and a bench-top laser optical particle counter (lab-LOPC). Microscope and lab-LOPC estimates of abundance and biomass were in close agreement. Crustacean production estimates were highest using Huntley-Lopez (0.20-185.3 mg C m-3 d-1), followed by Hirst-Bunker (0 .01-18.3 mg C m-3 d-1), chitobiase (0.05-15.6 mg C m-3 d-1), and Hirst-Lampitt (0.03-14.3 mg C m-3 d-1). Hirst-Lampitt-, Hirst-Bunker-, and chitobiase-based estimates of crustacean production and trophic transfer efficiency (TTE) yielded similar patterns/magnitude, while the Huntley-Lopez model was more variable. Estimates showed stronger agreement in 2011 than in 2010, attributed to the shift from El Niño to La Niña conditions. We highlight similarities/differences associated with these techniques and suggest that Hirst-Bunker estimates of production and TTE are most consistent with chitobiase-based values.