Plankton variability on the Faroe Shelf during the 1990s

A mixture of neritic copepod species, meroplanktonic larvae, and ichthyoplankton usually dominates the zooplankton on the Faroe Shelf during spring and summer. The ecosystem, however, is very much affected by the interannually variable influx of Calanus finmarchicus. During the 1990s, the plankton production, abundance, and species composition fluctuated greatly, the zooplankton biomass on the Shelf (which is mainly C. finmarchicus biomass) by a factor of 10. When the abundance of C. finmarchicus was high, the abundance of neritic zooplankton was generally low and vice versa. Interannually, there is a strong inverse relationship between zooplankton biomass on the Shelf and new primary production. During the 1990s, new primary production from spring to mid-summer fluctuated by a factor of about 5, inversely related to the zooplankton biomass. The good relationship between primary production and fish reproduction and growth is most likely the result of variable production of zooplankton of a suitable size for fish larvae during spring.