Bio-hazards
Ocean biohazards fall into several categories, of which the most important is the production of toxins by some species of algae under some circumstances. If these organisms proliferate they become known as toxic algal blooms which can have profound effects on seawater ecology and potentially human health.
Harmful algal blooms (HABs)
Algal blooms are an abrupt increase in algae and microscopic plankton. This happens when the light and nutrient conditions are right for growth. Most algal blooms are beneficial to the ecosystem but others can be harmful. Harmful algae are a small but diverse group of species and are found from freshwater to marine waters.
Some HABs produce toxic effects in humans and other animals. The toxic effects can be through shellfish poisoning or through contact with contaminated water. Some HABs have been linked to fish kills causing substantial economic losses to fisheries. Others cause harm through blocking the sunlight, needed by other species to grow, or through depleting oxygen. The term HABs also covers species that create nuisance conditions but are not necessarily toxic. This can include odours and discoloration of waters such as in large ‘brown tides’ or ‘red tides’.
Although their impact is large, the phytoplankton involved can be small; a microscope is needed to identify them. Blooms of some microscopic diatom species such as Pseudo-nitzschia spp. produce domoic acid and cause amnesic shellfish poisoning (ASP) affecting humans and other animals that eat contaminated fish. Other types of diatoms have "glass-like" siliceous spines that they use to float. In some species such as Chaetoceros convolutes the many needle-like spines are particularly irritating to gills and contribute to massive fish kills. Another type of phytoplankton, dinoflagelates have tiny whip like flagella that they use to propel themselves along. The dinoflagellate Alexandrium catanella produces a potent neurotoxin saxitoxin that can cause potentially fatal paralytic shellfish poisoning (PSP) if ingested. Other microscopic dinoflagellates, associated with ‘red tides’ include naturally occurring blooms of Karenia mikimotoi found around the UK coast in summer, which cause massive fish kills in some years. Some blue-green algae or cyanobacteria blooms can look like foam on the surface of lakes. They can produce hepatotoxins (which affect the liver) and affect humans who drink or swim in the water.
The conditions that cause the blooms to occur are not very well known and it is difficult to predict when and where these short lived blooms will occur. It is still not fully understood why some species trigger a production of toxins in some years but not in others. In a warming world there is a danger that HABs may increase as global climate changes may create conditions that favour HABs, such as increased temperature. Eutrophication, with increases in nutrient and pollutant input, may also affect the balance of toxic and non-toxic plankton groups as will the introduction of exotic species from ballast water or aquaculture. We may also notice more blooms as detection and monitoring method improve.
