A newly described toxic algal species on the South Coast
In April 1988 and March 1989, South Africa experienced its two worst recorded abalone mortalities, on the shores of the Betty's Bay Nature Reserve on the South Coast. Among other marine fauna, an estimated 30 and 40 tons of abalone were washed ashore during the 1988 and 1989 events respectively. Not only were adult abalone affected, but 2 day-old larvae and spat (3mm juveniles) also appeared severly affected. Associated with these mortalities were coastal blooms of a previously unrecoded dinoflagellate species, which imparted a dirty olive-green discolouration in False Bay and Walker Bay. |
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| At the same time, an aerosol toxin was also produced, causing beach-goers and seaside residents to suffer respiratory discomfort, including a burning sensation of nasal passages, difficulty in breathing, and eye, nose and throat irritations. Microscopic examinations of water samples of these blooms revealed a Gymnodinium species, which appeared to share several characteristics of a fish-killing dinoflagellate Gymnodinium mikimotoi sensu lato that is common in the northern hemisphere. A recurrent bloom of that species in False Bay in the summer of 1995/96 was particularly noxious to holidaymakers and seaside residents there. However, the concentrations of cells were not high enough to cause any abalone mortalities.
Following the recent revision of the genus Gymnodinium sensu lato, this dinoflagellate was described as Karen cristata Botes, Sym et Pitcher, using light and scanning electron microscopy, pigment analysis and DNA sequencing. The species is identical to the one that appeared in New Zealand waters in 1993. Characteristic features of K. cristata are the apical crest with the straight apical groove, an asymmetric hypocone, wthe central nucleus and that the cell is generally as wide as it is long. Pairwise distance comparison of LSU rDNA sequences of K. cristata with other Karenia species indicate close affinity to another New Zealand species, K. brevisulcata (Chang) G. Hansen et Moestrup. However, there are sufficient differences to warrent the description of K. cristata as a new species.
Monitoring over the past decade has shown that K. cristata is a resident component of the South Coast phytoplankton. Although the toxins of this species remain uncharacterized, its presence pose a continual threat to the operation of abalone farms on the south coast of South Africa.
Article by Lizette Botes
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