While the relative contributions of climate and enhanced nutrients to HAB formation are still under debate there is now a general consensus that ocean climate forcing is the dominant factor.

HABs have increased in some areas of the north-east Atlantic over the past 50 years, as the seas around Great Britain and Ireland have become warmer, especially since the mid-1980s. l There is regional variability within this trend and some places, such as the east coast of Britain, have experienced reduced incidences of HABs.

Expected higher temperatures, which may lead to better growth conditions, and increased stability, leading to increased water clarity in the future, has the potential to favour the growth of some toxic and other HAB species in UK waters.  However, for some HAB species such as Dinophysis, there is still a lack of knowledge on the controls of its life cycle.

The effects of storms (decreasing stability, lower light levels) and increasing nutrients due to greater runoff are less predictable and will most likely favour some species and be detrimental to others.  Some of the UK regions that are likely to be more susceptible to hydroclimatic fluctuations such as the eastern Irish Sea and estuaries such as the Fal are also thought to be vulnerable to elevated nutrient concentrations.

The geographic extent of phytoplanktonPlanktonic marine plants. Click for link to the SAHFOS Marine Climate Change Encyclopaedia species distribution has the potential to change as it has for other species, and the possibility of alien Species that would not naturally occur in a particular ecosystem. species is increased with the changing environment. There are still some uncertainties as to what governs the mechanisms that promote this range expansion.

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What is already happening - Medium

A variety of different HAB species exist which have the potential to impact UK waters. Currently there are very different levels of knowledge about the biological controls of each one. There is a great deal of evidence available on the occurrence of HABs, and general agreement that there has been an increase in the reported number of HABs and that many of these are primarily linked to climatic forcing. Thus this leads to a medium on both axes (amount of information and agreement) as to the level of confidence in what has already happened (the same as in last years report card)

What could happen in the future - Medium

The paucity of long term time series data, coupled with the fact that most observations occur when blooms are already established, means there is little information on the processes that lead to their development and, depending on the species, a sparsity of knowledge on life cycle, cell division and environmental cues. There is therefore a lack of consensus on what the climate change effects are likely to be. Modelling is, in consequence, at an early stage of development although there is now a general consensus that hydroclimatic forcing is the dominant factor behind bloom variability.

The clear linkage with temperature related effects of the dominant group causing blooms means that the level of confidence that HABs may increase with climate change is high. However, because each species is sublty different, there is little consensus on which climate change factors are most important and there is low agreement on the importance of other affects such as nutrient supply.

Thus a moderate for evidence and moderate (it is climate but which elements) for agreement becomes a medium level of confidence overall.

• Understanding the life cycle of the principal species so that predictions can be made as to the likely changes due to climate change.
• Understanding the rate of genetic adaptation to climate change.
• Understanding the mechanisms of dispersion and range expansion of HAB species into UK waters.

At present HABs are major economic problems for shell fisheries in Northern Europe. These species exist in UK waters and can impact the aquaculture industry; at present because of the relatively small size of the UK mariculture industry (compared to Spain and France) economic impacts are restricted to the regional areas in which these mariculture industries are established. Predictions are for the industry to increase and thus any potential increase in shellfish toxin producing HAB species will affect the sustainability of these industries. The possible increase in bloom events such as Karenia mikimotoi or any other phytoplanktonPlanktonic marine plants. Click for link to the SAHFOS Marine Climate Change Encyclopaedia species, that can result in fish kills may have implications for the Irish and Scottish finfish aquaculture industries, which have been impacted by these events in the past.

Robin Raine
Marine Microorganisms Research Centre, National University of Ireland, Galway, University Road, Galway, Ireland

Martin Edwards, Chris Reid
Sir Alister Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, Plymouth, PL1 2PB.

Eileen Bresnan
Fisheries Research Services Marine Laboratory, PO Box 101, 375 Victoria Road, Torry, Aberdeen, UK, AB11 9DB.

Liam Fernand
Centre for Environment,Fisheries & Aquaculture Science (Cefas), Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk. NR33 0HT, UK.