Research Document - 2001/110

Decadal Time-Series of Invertebrate Zooplankton on the Newfoundland Shelf and Grand Banks 1991-1999

By Dalley, E.L., Anderson, J.T., Davies, D.J.

Abstract

The invertebrate zooplankton of the Northeast Newfoundland shelf and Grand Banks was dominated by copepods that comprised over 80% of all the plankton. All zooplankton was low in abundance during the early part of the decade and peaked from 1997 to 1999, coincident with increased nekton abundance. The lower abundances of some smaller species, e.g. O. similis, are negatively biased in the early years by use of a larger mesh (.505 mm). However, even larger zooplankton whose catch should not be biased by mesh size, e.g. larger stages of C. finmarchicus, C. hyperboreus, chaetognaths amphipods, and euphausids, were all low in abundance in the early 90's. The most abundant copepod species were O. similis, followed by Pseudocalanus sp., C. finmarchicus, T. longicornis, and C. hamatus, all of which peaked in abundance from 1997-99. In terms of biomass the most dominant copepod was C. finmarchicus, which peaked in 1999. Although C. hyperboreus was relatively low in numbers compared to other copepods, its biomass, which peaked in 1994, was also significant due to its large individual size. Biomass of Oithona peaked in 1997, Temora in 1999. Cladocerans were the dominant other zooplankton peaking in 1997 followed by Limacina which peaked in 1996 and bivalve larvae which peaked in 1999. The ability of the 2 central or 4 more widespread lines to estimate mean abundance varied with species or group but generally was not reliable as an estimator of overall mean abundance due to relatively wide distributions. This type of pelagic survey with simultaneous sampling of invertebrate plankton and nekton, which is comprised mainly of planktivorous fish, offers potential in elucidating links between the annual productivity cycle and fish recruitment.

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