Molecular tools for monitoring harmful algal blooms.

The world's oceans cover 70 % of the Earth's surface, and their dominant populations, both numerically and biomasswise, belong to microscopic protists and prokaryotes. The marine phytoplanktons are major components of both groups and are, by definition, high dispersal taxa with large population sizes. Small photosynthetic organisms are responsible for the bulk of primary production in oceanic and neritic waters. Microalgae in marine and brackish waters of Europe regularly cause harmful effects, considered from the human perspective, in that they cause economic damage to fisheries and tourism. Cyanobacteria cause similar problems in freshwaters. These episodes encompass a broad range of phenomena collectively referred to as ‘harmful algal blooms’ (HABs). For adequate management of these phenomena, monitoring of microalgae is required. However, present day monitoring is time consuming and based on morphology as determined by light microscopy, which may be insufficient to give definitive species and toxin attribution. The public perception of harmful algal blooms is often that of eutrophication, where increased nutrient loading results in large biomass blooms, which have a consequent effect on water quality (anoxia) and the ecosystem through substantial alterations in both the benthic and pelagic ecology. All too often, events that directly or indirectly relate to increased nutrients, such as dead zones in the northern Gulf of Mexico, a huge clean-up operation following an Enteromorpha bloom off Qingdao in time for the Olympic sailing competition in 2008 or the knock-on effects of hydrogen sulphide toxicity caused by rotting vegetation following extensive growth of both macro(Ulva, Brittany coast of France) and micro(Phaeocystis, North Wales, UK) algae, find substantial room in the popular press. What is less well-known is that HABs caused by toxinproducing algae have not only a far more serious impact on the quality of life, but also they are entirely natural. Anthropogenic impacts on toxic HABs are limited to either their global spread through potential transport vectors, such as ballast water of ships, or because of alterations in the coastline resulting from the construction of harbours and marinas, particularly around the Mediterranean coast, which promotes the development of chronic dinoflagellate blooms, such as the paralytic shellfish poisoning (PSP) toxin producer Alexandrium. The global scale of toxin-producing microalgae should not be underestimated. For example, the most serious would be the numbers of human intoxications with ciguatera, caused by the dinoflagellate Gambierdiscus, is currently estimated at some 50,000 per year. Every year, one to two human deaths are linked to the ingestion of PSP toxins. Although these problems are restricted to the tropical/warm temperate sphere of the globe, it demonstrates the urgent need to be able to monitor and prevent toxic HAB events. In Europe, this is effected through a series of directives that require coastal member states to monitor water for toxinproducing species and their toxins in shellfish. Starting with the EU Shellfish Hygiene Directive 91/492/EEC, a series of directives was issued to include newly discovered toxins and stipulating the methods of analysis and maximum permitted levels in shellfish. The most important of these would be 2002/225/EC and 2074/2005 (pertaining to toxin levels and analysis and methods) and more recently 15/2011 Responsible editor: Philippe Garrigues