SPI-ing on the seafloor: characterising benthic systems with traditional and in situ observations

This work aimed to show that the sea bed of two environmentally-different regions of the North Sea varies both spatially and temporally with respect to their biological communities and bioturbation characteristics. The two contrasting sites studied were north of the Dogger Bank (ND) (85 m) and the Oyster Grounds (OG) (45 m). The physical environment varied between and within sites, mainly influenced by sediment chlorophyll a content and water temperature. Our data revealed that the depth of the apparent Redox Potential Discontinuity (aRPD) layer at OG varied between 2.2 cm in February and 6.5 cm in October; evidence of bioturbation activity (e.g., feeding voids) was observed within the sediment profile. In contrast, at the ND site the aRPD values ranged from 1.7 cm in February to 2.5 cm in May and feeding voids and infaunal burrows were restricted to sediment depths far shallower than those observed at OG. Communities at ND were dominated by a number of surficial-sediment dwelling polychaete species (e.g., Notomastus latericeus, capitellids) while those of OG were dominated by the brittlestar Amphiura filiformis, together with significant numbers of deeper-dwelling taxa such as the ghost shrimp Callianassa subterranea and the bivalve mollusc Corbula gibba. Our data imply that regions of the North Sea which experience dissimilar environmental conditions not only possess different infaunal communities but also contrasting seasonal fluctuations and bioturbation capacities. The ecological implications of these findings, including inferences for carbon and nutrient cycling, are discussed in relation to the wider North Sea ecosystem.