The effects of climate change on harmful algal blooms and plankton communities in the NE Atlantic.

Climate change has a profound impact on the phenology and abundance o f plankton in the NE Atlantic and North Sea. There is concern that harmful algal bloom (HAB) species may increase, accompanied by negative socio-economic impacts, including threats to human health and marine harvesting. We reviewed historical major UK outbreaks o f poisoning and attempted to examine the epidemiology on a finer scale by linkage o f hospital admissions, GP and pathology records. As expected the incidence o f shellfish poisonings was very low but accurate identification o f poisoning was generally unreliable. The current UK shellfish monitoring programme is the key indicator for monitoring trends in the risk o f human exposure.Using the Continuous Plankton Recorder (CPR) survey, we mapped spatial and temporal trends o f various phytoplankton, including HAB species, and zooplankton (Tintinnids and Calanus). We found fundamental shifts in the relative abundance of diatoms versus dinoflagellates, with a dramatic dinoflagellate decline in recent years. Northward shifts in abundance were found for some Tintinnid and Calanus taxa. Using criteria o f statistical causality, these changes were linked to climate, in particular sea surface temperature and increasingly windy conditions in the summer, with a notable non-linear interaction between these factors. Focusing on Calanus, we showed the strength o f statistical links between abundance and climate variables can wax and wane as the time series lengthens. We found tentative evidence for adaptation o f Calanus to climate change, but not at a level that could reverse overall long-term patterns.Links with climate are often argued to be proxies for unobserved mechanisms that determine species abundance, such as stratification. We developed a new stratification index, covering the whole NE Atlantic from 1970 to 2009. We propose that this has wide applicability in marine climate change studies. Throughout, our work demonstrates the importance o f consistent long-term ecological survey data