Harmful algal blooms

2003

YEAR BOOK

Home Page	Table of contents	Index by Author	Index by topics
	Search

The Martin Ryan Institute, NUI Galway

Robin Raine

Harmful algal blooms

Phytoplankton are microscopic organisms and the major form of plant life in the sea. They act as the 'grass' of the sea and are thus the ultimate determinants of the size of fish stocks. They are an important element in the global carbon cycle and are closely connected to global warming and other climatic effects which may be caused by greenhouse gases. Marine phytoplankton can proliferate into enormous concentrations of up to millions of cells per litre when sufficient light and nutrients are available. These events are referred to as blooms. Most blooms are extremely beneficial to the marine ecosystem as a primary source of food for the larvae of commercially important crustaceans and finfish, for the filter feeding bivalve shellfish such as oysters, mussels, scallops and clams, and for virtually every other form of marine life.

Potentially harmful phytoplankton: clockwise from top left - Dinophysis acuta, Alexandrium minutum, Karenia mikimotoi, Pseudo-nitzschia sp(x500).

A very small number of the several thousand phytoplankton species known to exist are potentially harmful. These can cause fish kills, contaminate seafood with toxins, pose a direct risk to human health, or otherwise alter ecosystems in ways that scientists perceive as harmful. These events are known as harmful algal blooms, or HABs. HABs are sometimes incorrectly called red tides, which is a misnomer, as the term 'red tide' refers to only one particular form of potentially harmful event when phytoplankton densities become so high that the sea becomes discoloured. The term Harmful Algal Bloom is likewise not at all precise, as a bloom implies a massive proliferation of phytoplankton cells. Some phytoplankton species contain toxins so potent that only a small number need be present in order to contaminate shellfish seriously enough to render them unsuitable, even dangerous, for consumption by humans.

A major public health problem caused by HABs around the Irish coast is associated with the contamination of shellfish with biotoxins. Ingestion by humans can result in a variety of serious and unpleasant syndromes. These are known as Diarrheic Shellfish Poisoning, for the most part caused by biotoxins present in Dinophysis, Azasparacid Shellfish Poisoning where Protoperidinium is implicated, Amnesic Shellfish Poisoning caused by the presence of domoic acid, a toxin which is produced by the diatom Pseudo-nitzschia, and Paralytic Shellfish Poisoning which results from ingestion of highly potent saxitoxins derived from Alexandrium. Another dinoflagellate, Karenia mikimotoi, is responsible for the formation of red tides which have caused mortalities of both marine fauna and of farmed finfish and shellfish around the coastline. Monitoring for the phytoplankton and their biotoxins is a costly and time-consuming process and is the responsibility of the Marine Institute.

Investigations into the occurrence of HABs have been carried out at NUI, Galway since the late 1980s. Research has shown that many harmful events arise from harmful populations which are carried into inshore areas from the open ocean by currents which are driven by surface winds. This has allowed a predictive element to HAB occurrences based on weather forecasts. The application of remote sensing by using satellite derived images of the sea surface has also been given a thorough appraisal.

A number of HAB projects have recently started within the Martin Ryan Institute at NUI, Galway. These have been funded through the Higher Education Authority Programme for Research in Third Level Institutions (Cycle 3) and the Marine Institute/National Development Plan programme. They involve the development of species specific molecular probes for the rapid detection of harmful species, modelling the dynamics of Alexandrium , and BOHAB: the Biological Oceanography of Harmful Algal Blooms.

Monitoring phytoplankton using traditional light microscopy techniques is a highly skilled and time-consuming process. In addition, the similarity in the appearance of many species within a particular genus means that on occasion more sophisticated identification techniques such as electron microscopy are essential. The development of fluorescent dyes which attach to the nucleic acid of a single species will greatly ease the process. Collaborative work with the National Development Corporation laboratory situated on campus at Galway is currently underway developing probes for Alexandrium and Pseudo-nitzschia.

The life cycle in Alexandrium: the diploid cyst, dormant at the seabed, excysts and forms two haploid vegetative cells, which divide vegetatively until they form gametes, which fuse to eventually produce the diploid cyst; diploid phases of the life cycle are in blue

A common Alexandrium species found in Irish waters is Alexandrium tamarense. A second toxic species, Alexandrium minutum also occurs. The life cycle of this genus is reasonably well understood in that there is a dormant overwintering stage known as a cyst. These cysts overwinter in the sediment where they can remain viable in the anoxic muds of inshore bays for years. When environmental conditions are suitable, the cyst germinates into the vegetative planktonic stage which causes the toxicity. Research is initially focusing on how temperature and an endogenous biological clock affect excystment rates. The annual cycle of the occurrence of this species in the water can then be modelled mathematically.

BOHAB is a three year programme which is aimed at establishing the link between oceanography and the development of harmful blooms along the west coast of Ireland. With partners from the Marine Institute and the Woods Hole Oceanographic Institution, USA, scientists at the Martin Ryan Institute are studying the dynamics of harmful events, specifically looking at the relationship between changes within phytoplankton communities, levels of toxin within shellfish tissue, and oceanographic events. The work incorporates use of the research vessel Celtic Voyager for field studies, the deployment of moored oceanographic instrumentation and studies on the life cycles of harmful species, and is complemented by ongoing research within the partner institutions.

Contact: Dr Robin Raine, The Martin Ryan Institute, NUI Galway; E-mail: [email protected]