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Toxic marine microbes

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An Impact Larger Than Life: Associate Professor Shauna Murray, from the Plant Functional Biology and Climate Change Centre at the University of Technology Sydney, is currently a Future Fellow, an Australian research council funded fellowship position that enables her to focus solely on her research for the next four years. Many single-celled marine eukaryotic microbes produce various types of toxins that can cause problems in the marine environment, and for the seafood industry. One algal bloom in Tasmanian last year, caused by a dinoflagellate, Alexandrium tamarense, a type of microalgae, cost the seafood industry $25 million when the neurotoxins the bloom produced found its way into the shellfish food chain.

Scanning electron microscopy image of dinoflagellate Alexandrium diversaporum. Photo by Mona Hoppenrath. 
This affected the oyster, mussel, abalone and rock lobster industries and caused Japan to initially ban all imports of Australian seafood for a year, until the problem was sorted out.
Most states and territories now have monitoring systems to check the health of marine habitats, especially those that are linked to the areas with shellfish farms or shellfish harvesting.

Interestingly, US research has shown that those shellfish living in areas with a history of algal blooms can be less affected by the toxins, compared to shellfish without that history of exposure, which are more susceptible. The blooms are becoming more prevalent in Australia, and while there are a number of causes for this, it seems the increase in aquaculture means that more attention is being paid to areas where the seafood industry operates.
Climate change is also playing a part with certain species moving further south into areas like Tasmania whereas before they were found on the coast of NSW. There also appears to be a lengthening of the time window in which the blooms can occur and when they occur. The triggers for each bloom depend on the species themselves. Some, like the Alexandrium species that affect shellfish, lie as cysts in the sediments under the sea, only blooming when the right temperature, day length and salinity conditions coincide, which might be in September each year, allowing the cysts to germinate and reach the surface. These types of blooms often recur at the same sites at the same times of the year.

Red tide: Accumulation of single-celled dinoflagellate Noctiluca scintillans at Clovelly Beach, Sydney, November 2012. Photo by Gurjeet Kohli.

Other species are fast responders to any kind of increased nutrient levels like those that an oceanic upwelling can create, and still others are very buoyant, accumulating with winds and tides. One such floating bloom of the marine dinoflagellate species Noctiluca scintillans, was very widespread along the Sydney coast in November 2012, its bright red colour leading to the name “the tomato soup” bloom.
The toxins that these marine microalgae produce do protect them from predators like the tiny crustacean copepods, but they also have other uses. One species, Amphidinium carterae, produces toxins that have pharmacological properties, some toxins being antibacterial and some being antifungal. Other species like Karlodinium micrum, are being investigated as treatments for various things like cystic fibrosis.

Oyster farms in the Hawkesbury River, Sydney region. Photo by Hazel Farrell.

Every toxin has different impacts on the food chain. Some are toxic to fish while others are not. The toxin saxitoxin, for instance, which was produced by Alexandrium tamarense, accumulates in mussels is not generally harmful to fish, whereas it is for humans. Korea and Japan have had huge problems with other toxins from blooms that have killed many fish in their large, sea-based fish farms. The toxins can either be water soluble or fat soluble. The water soluble ones like saxitoxin can leave seafood like oysters and mussels relatively quickly, those creatures usually being toxin free in about a week. The fat soluble ones, such as the toxins involved in ciguatera fish poisoning, can take longer to disperse, taking months to disperse from crustaceans like rock lobsters. In either case they have a very large impact on the seafood industry for such a tiny organism.

Training workshop on microscopy and identification of phytoplankton, 2012. Photo by Gurjeet Kohli.

There is still much to know about theses micro algae, especially given that the toxins they produce require a lot of energy. The toxins are also highly complex chemicals, one, maitotoxin, being the most complex natural substances known and produced by one single-celled species of algae.
Associate Professor Murray is currently researching an algae which is causing fish poisoning in many Pacific islands, affecting up to 30% of island populations. The research is looking at the identification, diversity, ecology and abundance of the micro algae, as well as the genetic factors related to the production of toxins in the species.
The impact of such micro-organisms is larger than life.

Associate Professor Shauna Murray was interviewed for A Question of Balance by Ruby Vincent. Images provided by Dr Murray. Summary text by Victor Barry, February 2014.

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