Mesozooplankton community seasonal succession and its drivers: Insights from a British Columbia, Canada, fjord

The mesozooplankton dynamics in Rivers Inlet, a fjord in Central British Columbia, Canada, were studied from March to June of 2008, 2009 and 2010 to assess the interannual, seasonal, and spatial variability in zooplankton abundance and community structure under different physical environments and spring bloom scenarios. Samples were collected fortnightly during 2008–2009 and monthly in 2010 and provide one of the few multi-year zooplankton time series in the region. Two distinct zooplankton communities characterized the observed succession pattern. The winter–spring group was described by the presence of small, year-round omnivorous zooplankton: bryozoan cyphonautes, Microcalanus spp., Microsetella spp., Oithona spp., and Oncaea spp., as well as by large, diapausing copepods such as Eucalanus bungii, Neocalanus plumchrus, and Calanus marshallae and the euphausiids Thysanoessa spinifera. By contrast, the spring–summer community showed an increased abundance of Acartia longiremis, cladocerans, Limacina helicina, Metridia pacifica, Euphausia pacifica, appendicularians, Clione limacina, chaetognaths, polychaetes, Pseudocalanus spp., ostracods, and amphipods. The timing of zooplankton succession was consistently associated with the timing of the spring bloom, and was delayed in 2009 when the spring bloom occurred in May rather than April. The zooplankton succession dynamics are discussed in terms of dominant feeding guild structure to highlight the potential mechanisms of succession. Spatial variability in zooplankton distribution was mainly influenced by river flow and exchanges with adjacent coastal waters.

► We examine seasonal variation in zooplankton composition in a British Columbia fjord.
► We observed a recurrent zooplankton succession pattern in the three years of study.
► The winter–spring community is dominated by small, year-round omnivorous taxa.
► The spring–summer community is characterized by winter omnivorous/spring herbivorous taxa.
► The timing of succession was associated with the timing of the spring bloom.