Defra - Department for Environment, Food and Rural Affairs.

Science Search

Science and Research Projects

Return to Science Search homepage   Return to Project List

Harmful Algae, Nuisance Blooms and Anthropogenic Nutrient Enrichment - ME2208

Phytoplankton is the collective name given to the microscopic floating plants in seas and lakes. Under certain conditions, the abundance of phytoplankton as a whole or of one or more species in particular, can reach a magnitude at which it is visible through discolouration of the sea. Some of these blooms because of the colour of the water have been called 'Red Tides'.

Blooms of some 300 species of the phytoplankton are known as Harmful Algal Bloom (HAB) species in recognition of their potential impact on ecosystem health, human health and the human use of the marine environment. Harmful effects may result from the large biomass (amount of algae) present or the highly toxic compounds produced by some species.

As large biomass blooms decline and cells settle to the sea bed this can result in smothering of plants (sea weeds and sea grasses) growing attached to the seabed in near shore waters. The decomposition of cells uses oxygen and on occasions leads to deoxygenation of bottom water and death of animals living in and on the sediment. HAB species which produce toxins can cause problems even when the phytoplankter (individual species) is present in low numbers (a few hundreds of cells per litre). Toxins can be transmitted to humans via plankton-feeding bivalves such as mussels and cause human illness and in extreme case death. In addition, the regular occurrence of these species causes difficulties for shellfish aquaculture, commercial and recreational harvesting of wild shellfish through temporary prohibitions on harvesting when threshold levels of toxin are detected in shellfish tissue. Toxin producing algae and large biomass blooms have also caused financial loss to the fish farming industry in many countries. Mass mortalities of farmed fish have been caused by direct toxicity, damage to gills leading to asphyxiation (caused by cells with long spines) and oxygen depletion.

Over the last 25 years, a number of reports and scientific publications have reported a putative increase in the occurrence of harmful algal blooms and incidents relating to biotoxins. This has led a search for the probable cause and anthropogenic nutrient enrichment of coastal waters is one which has received much attention. There is however no clear consensus. A link between HABs and enrichment is evident in some coastal waters but not in others. However, it is the presumption that the former is broadly applicable to coastal regions that has led to the view that the occurrence of HABs diagnoses the undesirable consequence of anthropogenic nutrient enrichment.

There is a clear need to examine the scientific justification for this presumption, if HABs and HAB species are to be used as indicators of ecosystem health (e.g. eutrophic as defined by the Urban Waste Water Treatment Directive and OSPAR Strategy to Combat Eutrophication). This is the overall objective of the study proposed, namely to review the relationship between HABs and anthropogenic nutrient enrichment. The aims are to: i) identify examples where enrichment has led to changes in HABs and HAB species; ii) characterise the underlying physico-chemical (ecohydrodynamic) conditions of these coastal regions which support an enrichment effect; iii) use the information gained to determine those ecohydrodynamic conditions under which enrichment is more likely to have an influence on HABs and HAB species dynamics. The relationship between HABs, ecohydrodynamics and nutrient enrichment will be examined in detail using selected phytoplankton data sets from UK, Irish and Norwegian waters.
Project Documents
• Final Report : ME2208: Final report Anthropogenic nutrient enrichment and blooms of harmful micro-algae   (4078k)
• Abstract : What is a Harmful Algal Bloom, and can it be used as an indicator of anthropogenic nutrient enrichment in marine waters?   (357k)
Time-Scale and Cost
From: 2008

To: 2009

Cost: £74,514
Contractor / Funded Organisations
Fisheries Research Services, Agri-Food and Biosciences Institute, Institute of Marine Research, Scottish Association for Marine Science, CEFAS, University of Rhode Island
Ecosystem Functioning              
Environmental monitoring              
Environmental Protection              
Marine Organisms              
Monitoring and evaluation              
Toxic Substances              
Water quality monitoring              
Fields of Study
Environmental Protection - Marine