The presence of Gambierdiscus spp. in Pakistan waters; Morphology and species

The cause of ciguatera fish poisoning (CFP) is believed to be toxins produced by a dinoflagellate of the genus Gambierdiscus (Dinophyceae). These species are armoured unicellular , photosynthetic, toxic (as you might of gathered by now) and distributed in tropical waters often in reefs. Their preferred habitat is attached to the surface of algal turf, detritus and sand. In the tropics CFP is a problem surrounding many reef islands, were they rely on fish as a protein source. As mentioned in my last blog post about the physiological responses the symptoms are: gastrointestinal, neurological and cardiovascular. This papers estimate of the amount of annual cases is 50 k, this is much lower than Shoemakers et al. (by 50 k) which is misleading, this may be due to underreporting in the references chosen.

The identification of Gambierdiscus spp. is complex as I could imagine being so small and similar, the species are grouped into two main morphologies: anteroposterior compressed cells e.g. G.toxicus, G.belizeanus, G.australes, G.polynesienus, G.pacificus, G.coralinianus and globular shaped cells such as G.yasumotoi and G.ruetzelri. The purported distinguishing features, which set these groups apart is dependent on the ornamentation and shape and size of cell plates. Munir et al.’s work is the first work to document the presence Gambierdiscus spp. in the northern parts of the Indian Ocean, Pakistan. Their research describes the basic morphology of these toxic benthic dinoflagellates, from two coastal regions one mangrove and one coral habitat.

Five species of Gambierdiscus were found: G. toxicus, G. belizeanus, G. polynesiensis, G. australes and G. yasumotoi. Cells of G. toxicus are described as round from an antapical and apical view and also ventrally flattened. Cell size is 71-96 micrometres dorsoventrally and 62-90 micrometres in transdiameter. Epithecal plates are comprised of 11 pore plates which are variable in shape and size. The plates have various morphometrical defining parameters. G.belizeanus cells are round and also ventrally compressed. They are smaller in size and range from 50-70 micrometres dorsoventrally and 65-69 micrometres in transdiameter. The plate surfaces are aerolated and display dense pores. Cells of G. polynesiensis are elliptical, and cell size is 65-88 micrometres and 56-75 micrometres in dorsoventral and transdiameter respectively. The epithecal plates are different taking on a triangular structure. G. australes cell size is 60-81 micrometres and 48-76 micrometres dorsoventral diameter and transdiameter respectively. The epithecal plates are smooth. Cells of G.yasumotoi are in contrast globular shaped in epical view, and the plates are smooth with numerous pores. Cell size is 49-52 micrometres long, and 43-51 micrometres wide. The authors also document variations in plate measurements and various other identifying morphological characteristics.

The documentation of dinoflagellates off the Pakistani coast recorded 79 different species of dinoflagellates that were not identified to genera level. Defining these species may help in understanding the distributions of toxic species, which have implications for the fishing industry. The species of Gambierdiscus that Munir et al. discovered in Pakistani coastal waters were previously thought only to be found in Atlantic and Pacific waters. There are still regions of the coast where research is not available which could be detrimental to local fishing. The authors note that macroalgae are the preferred habitat for these benthic dinoflagellates, therefore this study drastically underestimates the possible ecological relevance of these species. The aim of their research was to provide evidence of their presence in this region to alert fisheries and resource managers. They advise further research that emphasises documenting the abundance and distribution of these species and potential impacts on fish community structure. They also advise developing databases to promote regional assessments for socioeconomic understanding of the status of these toxic species and for promoting export management. This work is fundamental to understanding the danger of CFP, by raising awareness of its presence. This is an eye opener that demonstrates we really don’t have it all pegged; understanding Gambierdiscus blooms and fish grazing ecology, in conjunction with artificial neural network databases of trophic biomagnifications, could help prevent CFP.

Munir, S., Siddiqui, P. J. A. & Morton, S. L. (2011). "The occurrence of the ciguatera fish poisoning producing dinoflagellate genus Gambierdiscus in Pakistan waters." Algae 26: 317-325.