JPR Advance Access originally published online on April 19, 2006
Journal of Plankton Research 2006 28(7):695-705; doi:10.1093/plankt/fbl006
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Correspondence among methods of zooplankton biomass measurement in lakes: effect of community composition on optical plankton counter and size-fractionated seston data
Groupe de Recherche Interuniversitaire en Limnologie et en Environnement Aquatique (GRIL), Départetment de Sciences Biologiques, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec, Canada H3C 3J7
Present Address: Department of Biology, University of Regina, Regina, Saskatchewan, Canada S4S 0A2
* Corresponding Author: alain.patoine{at}uregina.ca
Received August 6, 2005; accepted in principle January 31, 2006; accepted for publication April 4, 2006; published online April 19, 2006
Communicating editor: K.J. Flynn
The effectiveness of the optical particle counter (OPC) to estimate zooplankton biomass depends on the variability in zooplankton shape and the presence of interfering particles. In marine environments where zooplankton are composed of similarly shaped copepods, an average shape is relatively easily obtained. However, in freshwater environments, spheroid cladocerans mix with ellipsoid copepods and make the application of a single morphometric model difficult. To expand the use of the OPC to freshwater environments, we developed new ellipsoid models for three common lake types (eutrophic, mesotrophic, and oligotrophic). In addition, we assessed how closely different size fractions of seston corresponded to zooplankton biomass. When expressed in common dry mass units, OPC- and seston-derived zooplankton biomass estimates showed a 1:1 correspondence with taxonomically derived estimates in productive lakes (r > +0.70, P < 0.001) but not in oligotrophic systems. OPC ellipse models differed among lake sets (major-to-minor axis ratio: 1.5 to 2.7) but were not a simple function of the cladoceran-to-copepod ratio. The seston size fraction that provided the best estimates of zooplankton biomass was smaller in mesotrophic lakes (>200 µm) than in eutrophic or oligotrophic lakes (>500 µm). The presence of algae and rotifers had no detectable influence on OPC and size-fractionated seston estimates. Overall, these analyses suggest that OPC and seston provide reliable estimates of lacustrine zooplankton biomass as long as region-specific ellipse models and size fractions, respectively, are used.