The seasonal development of the zooplankton community in a British Columbia (Canada) fjord during two years with different spring bloom timing

Variability in phytoplankton and zooplankton dynamics were studied during spring and early summer of 2006 and 2007 in Rivers Inlet, a fjord on the central coast of British Columbia, Canada. The onset of the spring bloom was shifted by 3 weeks in 2007 (26 April) compared to 2006 (7 April). The later 2007 bloom was accompanied by a later and lower zooplankton biomass peak and a different zooplankton composition. Mean spring–summer total zooplankton biomass was 57 and 27 mg m−3 in 2006 and 2007, respectively. This was explained by reduced juvenile densities and changes in dominance of most abundant zooplankton taxa in the fjord. Between 2006 and 2007 mean densities of copepod nauplii and calanoid copepodites decreased from 224.3 to 95.8 and from 197.7 to 35.9 ind. m−3, respectively. Adult Calanoidae and Metridinidae decreased in abundance while densities of Acartiidae and Ectinosomatidae increased. We postulate that the later bloom delayed the seasonal increase in zooplankton biomass by inhibiting the survival of early developing stages of certain zooplankton species through a mismatch between their appearance and the spring bloom. This study provides the first baseline observation on the temporal scale of zooplankton phenological changes in the region.