Broad-scale distribution of the winter protozooplankton community in the North Sea

Protozooplankton (PZP) (here size range: 12-200 mu m) are rarely sampled over a broad scale, especially in ecosystem monitoring programs, despite their trophodynamic importance as grazers in the microbial loop and as prey for larger zooplankton and early life stages of fish. In this study we sampled PZP from Dutch, French, German and Norwegian research vessels taking part in the annual ICES coordinated International Bottom Trawl Survey (IBIS) which provides data on fish stock abundances and status for the entire North Sea. The abundance, biomass, composition and distribution of PZP were examined at 39 stations across the North Sea (from 3.2 degrees W to 7.6 degrees E and 50.5 to 59.8 degrees N) in mid-winter (January-February 2014), a period of the year which is under-investigated so far. Twenty four taxa of dinoflagellates and ciliates were identified. Two groups comprised 89% of the total abundance of PZP: Gymnodinium spp. and other athecate dinofiagellates (68%) and Strornbidium spp. and other naked ciliates (21%). The biomass of PZP at each station ranged between 0.08 and 2.4 mu g C L-1, which is much lower than that reported for spring or summer (>= 100 mu g C L-1) in the North Sea. Relatively small-sized (< 40 mu m) PZP contributed 46% of the total biomass. No significant spatial pattern in the composition of the PZP community was found, although the total abundance of tintinnids was highest in the southern North Sea, an important over-wintering area for marine fish larvae. Using this fish survey (IBTS) as a sampling platform allowed us to obtain a synoptic view of the PZP community over a large area. The present collaborative effort provides an example of how existing monitoring platforms can be augmented in the future to collect relevant data and potential ecological indicators needed to advance the ecosystem-based approach to managing marine systems