thousands of fish in North Carolina and the Chesapeake Bay in the us have been killed by Pfiesteria , a dinoflagellate (unicellular, pigmented, aquatic organisms). This phenomenon is being attributed to an increase in the amount of nitrogen, phosphorus and other nutrients that wash off the land from fertilisers and animal wastes, sewage and effluent pollution in oceans, dam construction, and the increase in water traffic. However, Pfiesteria is only one of the numerous toxic phytoplankton that plague the world's waters.

Ocean blooms, resulting from pigments that are released during photosynthesis, are the most dramatic evidence of phytoplankton activity. Cyanobacteria, commonly known as blue-green algae, is not always blue-green. It derives its name from the variety that inhabits the Red Sea, causing frequent blooms.If consumed, these produce brevetoxins (neurotoxic chemi-cals that harm a protein channel in the nerve cells of muscles, leading to paralysis). Chrysophytes (golden-brown algae) do not produce neurotoxin but do cause brown tides that shade marine plant life and drastically affect the marine food chain (Environment , Vol 39, No 10).

What makes matters worse for scientists trying to deal with the problem is Pfiesteria's complex makeup, which makes it extremely difficult even for simple identification. Scientists have been trying to develop identification techniques based on Pfiesteria's molecular characteristics rather than its appearance.

Recently, the us Geological Survey and the University of Maryland's Center for Environmental and Estuarine Studies have made an interesting discovery in their analysis of sediment samples collected from Chesapeake that date back to thousands of years. They contain many dinoflagellates and other microbes that offer a baseline of environmental conditions to measure against current data.