Habitat partitioning by fish larvae among coastal, offshore and frontal zones in the southern North Sea

This study compared marine and estuarine larval fish assemblages among nearshore, offshore and frontal habitats of the southern North Sea. In late June and early July 2005, parallel cruises collected larvae along offshore transects crossing tidal mixing and river plume frontal zones in the German Bight, and at shallow nearshore stations within the Wadden Sea and associated estuaries of major tributaries. A mixture of larvae from 17 species occurred including the (then) newly re-established 'southern' clupeids (European sardine Sardina pilchardus and anchovy Engraulis encrasicolus) as well as traditional North Sea species such as horse mackerel Trachurus trachurus, solenette Buglossidium luteum and various species of gobies. Multivariate statistics on taxonomic composition indicated that shallow and deep areas were 2 distinct habitats. Wadden Sea stations had a conspicuously different species composition and low species richness compared to all deeper areas. In deeper waters, species composition was similar regardless of frontal strength, and larger larvae occurred most frequently in the cooler areas of the German Bight. Altered species composition observed at some nearshore stations indicated that frontal dynamics and tidal advection may lead to expatriation of larval fish to presumably less favorable areas. Frontal habitats in the German Bight may not necessarily promote higher survival of larval fish than other areas but appear to form important boundaries between species-rich, deeper waters of the German Bight and relatively species-poor, shallower waters of the Wadden Sea.