[Coral-List] nutrients/ herbivory/toxic dinos/ciguatera & coral reef health
mark_skinner59 at yahoo.com.au
Thu Mar 27 08:50:26 EDT 2008
Impact of Cigutoxic dinoflagellates on coral reef health degradation, the unseen, & major influence!?
Hypotheses have been put forward as to the reasons for the toxicity of benthic epiphytic dinoflagellates. In terms of evolutionary ecology it would make sense for an organism to protect its host, in this case macroalgae (or turfalgae) from herbivory by fish and invertebrates. Indeed we know that macroalgal secondary compounds deter grazing, and then there is no reason to doubt that dinoflagellate toxins have the same effects. As there appears to be no specificity in host-epiphyte interactions it would appear that selection pressures may work to support the overall dominance of macroalgal over coral reef ecosystems. Toxic dinoflagellates like their hosts are at the bottom of every food chain that they are associated with when a coral reef becomes degraded, for a variety of reasons and macroalgae become more dominant. Whether it be natural succession to algal dominated reefs due to disturbances from cyclonic weather conditions and natural predation or from anthropogenic
causes, from climate change, eutrophication or any combination of influences that may initiate coral reef degradation.
As an hypothesis, the succession/decline of a coral reef to one that is algal (or even more advanced cyanobacterial) dominated is furthered by dinoflagellates as the toxins could be capable of sublethal impacts(such as fecundity) on any of the food web communities that would normally be found on a healthy coral reef. Those toxins could be responsible, through a variety of sublethal impacts, for the potential decline of organisms at higher tropic levels in a coral reef ecosystem subject to degradation. Toxins may also play a role in promoting preferential predation dependent upon factors such as feeding strategies and herbivore physiology. Hence the coral reef succession to algal dominance could be caused by and reinforced by dinoflagellate toxins. The alternate hypothesis to this is that those toxins cold be a byproduct of community change. The end result, the coral reef communitys biodiversity, may be rapidly lost and one output more easily recognised is further
ciguatera fish poisoning outbreaks.
Study has been done on the various toxins that have impacted on mans use of seafood, from ciguatera to the types of shellfish poisoning in terms of identification and their sources. Not surprisingly many of the toxin sources, those genera of toxic dinoflagellates, including Prorocentrum, Gambierdiscus & Ostreopsis, have been found in macroalgal samples from degrading coral reefs and lagoons (first hand study has included Tahiti, Rarotonga, Aitataki, Vita Levu, Palawan, Bali, Pari, Gili Trawangan, Heron, Fraser, Green, Fitzroy, Normanby, Snapper, Magnetic, Hinchenbrook and Double Islands) throughout all tropical regions. Whilst research has leaned towards mitigating the impacts on human health, there must be a greater effort to look into the role of these toxins in coral reef ecosystem management. We hold the conservation of coral reef ecosystems of the highest importance for so many reasons then we do need to take on board more research which will look into the
hypothesis presented here as it may be the key as to why coral reefs may decline in such rapid circumstances. It can take less than a decade for a coral reef to be altered and any reversal to its original condition, let alone its initial degradation, may very well be dependent upon the presence of dinoflagellate toxins.
I am looking to discuss this further with researchers and business operators who have similar concerns, with a view to obtaining support for research which would include the toxic dinoflagellate monitoring of coral reefs either with research already established in coral reef conservation and management or indeed to establish such research either on a local scale, at the GBR and/or further abroad.
Mark Skinner, EnTox , GEOHAB (IOC/UNESCO) endorsed research (mark_skinner59 at yahoo.com.au).
Get the name you always wanted with the new y7mail email address.
More information about the Coral-List