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

Lian E. Kwong*, Karyn D. Suchy, Akash R. Sastri, John F. Dower, Evgeny A. Pakhomov

*Corresponding author:

ABSTRACT: Zooplankton production estimates are necessary to understand the availability and transfer of energy for 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, group, stage or size class of zooplankton. We compare two methods for estimating crustacean production: the chitobiase method (based on a crustacean molting enzyme), and three empirical growth rate models (Huntley & Lopez 1992 [Huntley-Lopez]; Hirst & Lampitt 1998 [Hirst-Lampitt]; Hirst & Bunker 2003 [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 optic 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. 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 Huntley-Lopez 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 the Hirst-Bunker estimates of production and TTE are most consistent with chitobiase-based values.