Long-term trends in calcifying plankton and pH in the North Sea.

Relationships between six calcifying plankton groups and pH are explored in a highly biologically productive and data-rich area of the central North Sea using time-series datasets. The long-term trends show that abundances of foraminiferans, coccolithophores, and echinoderm larvae have risen over the last few decades while the abundances of bivalves and pteropods have declined. Despite good coverage of pH data for the study area there is uncertainty over the quality of this historical dataset; pH appears to have been declining since the mid 1990s but there was no statistical connection between the abundance of the calcifying plankton and the pH trends.

The potential of producing heterotrophic bacteria biomass on aquaculture waste.

The effluent from the drumfilter of a recirculation aquaculture system was used as substrate to produce heterotrophic bacteria in suspended growth reactors. The effects of organic carbon supplementation (0, 3, 6, 8 g/l sodium acetate) and of hydraulic retention times (11-1h) on bacteria biomass production and nutrient conversion were investigated. Bacteria production, expressed as volatile suspended solids (VSS), was enhanced by organic carbon supplementation, resulting in a production of 55-125 g VSS/kg fish feed (0.