"The existence of paralytic and diarrhetic shellfish poisons (PSP and DSP respectively) in shellfish is well established.
In 1987, an amnesic shellfish poison (ASP) came to widespread attention as a result of adverse human health effects on consumers of cultured mussels from Prince Edward Island, Canada. The culprit in this case was domoic acid produced by marine algae.
This increased the awareness of the possibility of natural neurological poisons occurring in seafood products, and of the likelihood that there may be other naturally-produced organic compounds posing risks to the health of seafood consumers.
In the last decade, much greater attention has been given to harmful algal blooms (a more all-encompassing term commonly used to describe blooms having a range of adverse effects from purely aesthetic to the production of toxins), partly because of dangers to human health, but more directly because of effects on valued marine species such as cultured finfish.
While the topic of such natural poisons is not of prima facie relevance to marine pollution from land-based sources, the contention that the frequency and ubiquity of unusual algal blooms is increasing has given rise to suspicions that there may be a connection with eutrophication.
These suspicions relate to the increased influx of nitrogen compounds to the ocean resulting from anthropogenic activities, although a direct link with the frequency of unusual algal blooms has not been established.
The transfer of the cysts of potentially toxic dinoflagellates in ballast water from one marine coastal area to another is also of concern: it is discussed below under the topic of invasive species.
Ubiquitous or large-scale eutrophication remains an issue of concern particularly in the context of increased nuisance algal blooms in the coastal zone.
The debate about whether there has been a global increase in the frequency and location of nuisance algal blooms continues. Increasing agricultural production based on the enhanced use of fertilizers could reasonably have been expected to provide increased fluxes of nitrogen and phosphorus into coastal areas through runoff.
However, the declining use of phosphorus compounds in detergents would be expected to result in some decline in phosphorus inputs to the ocean.
Some of the critical questions in this debate are: "Has there been a recent increase of the nitrogen-phosphorus ratio in runoff?" "Is phosphorus limitation of algal growth becoming more common than hitherto?" and "Does phosphorus limitation of growth, as opposed to the more common nitrogen limitation, give rise to metabolic responses in primary organisms that result in the production of toxins?"
Source: GESAMP71:32-33
GESAMP (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/ UN/UNEP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection). 2001. Protecting the oceans from land-based activities - Land-based sources and activities affecting the quality and uses of the marine, coastal and associated freshwater environment. Rep. Stud. GESAMP No. 71, 162 pp. ISBN 82-7701-011-7.