Assessment of Ciguatera Dinoflagellate Populations: Sample Variability and Algal Substrate Selection

¹ Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543
² Unite INSERM 303, Marine Station, 06250 Villefranche Sur Mer, France

Preliminary assessment is made of two key components in ciguatera ecology. First, we examined the numerical variability of Gambierdiscus toxicus as an epiphyte on the macroalgae, Dictyota and Galaxaura. Variability was examined by a statistical bootstrap technique to determine the minimum number of samples required to adequately estimate the abundance of G. toxicus at one station and to test for statistically significant differences between two stations. A minimum of 10 replicates were needed at the relatively low G. toxicus abundance found at our study site. Second, we demonstrated the feasibility of conducting controlled laboratory experiments to assess the short-term colonization behavior of G. toxicus on selected macroalgae offered in varying mass and surface area ratios. To assess G. toxicus abundance and distribution, the number of cells per unit of host alga must be standardized. We show that contradictory conclusions can be reached depending on whether the number of dinoflagellate cells is normalized to algal biomass or surface area.