M. Chinain et al., Seasonal abundance and toxicity of the dinoflagellate Gambierdiscus spp (Dinophyceae), the causative agent of ciguatera in Tahiti, French Polynesia, MARINE BIOL, 135(2), 1999, pp. 259-267
The benthic dinoflagellate Gambierdiscus spp. is the primary causative agen
t of ciguatera fish poisoning in French Polynesia. However, the initiation
of ciguatera outbreaks and the factors that control ciguatoxin production i
n this dinoflagellate are still poorly understood. In this paper, we presen
t some original data concerning the seasonal abundance and toxicity of natu
ral populations of Gnmbierdiscus spp. based on a long-term survey in a cigu
ateric site of the island of Tahiti. From February 1993 to December 1997, G
ambierdiscus spp. population densities were monitored weekly in the Atimaon
o barrier reef of Papara in relation to temperature and salinity. Densities
peaked at 4992 cells g(-1) in October 1994 and constituted greater than or
equal to 1000 cells g(-1) on several occasions. A total of 58 blooms were
recorded in the area, of which 65% occurred in 1995 and 1996 alone. Our dat
a confirmed the high endemicity of Gambierdiscus spp. in the Papara area. R
efined analysis of our raw data by a principal-component analysis of proces
ses (PCAP) revealed a seasonality in cell densities from February 1993 to M
ay 1995. During this period, Gambierdiscus spp. populations tended to reach
maximum abundance at the beginning and end of the hot season. In contrast,
salinity did not appear to be a determining factor in the seasonal abundan
ce of this dinoflagellate. The noticeable increase in both peak densities a
nd frequency of blooms further noticed in 1995 and 1996 was preceded by unu
sually high water temperatures in January to April 1994, concomitant with a
severe coral-bleaching episode. During the course of the study, a total of
303 x 10(6) cells obtained from 48 successive blooms was harvested. Toxici
ty screening revealed that toxin production was maximum from October 1994 t
hrough December 1996. No correlation was found between toxicity of these bl
ooms and their biomass nor the seasonal pattern of temperatures. It is sugg
ested that the toxicity of naturally-occurring blooms of Gambierdiscus spp.
and, consequently, the severity of ciguatera incidents in a given area, is
mainly dependent on the clonal nature of cells which coexist within local
populations of this dinoflagellate.