A potentially toxic epiphytic dinoflagellate assemblage on macroalgae was studied for 1 yr in a shallow protected rocky habitat in Palamós (Costa Brava, NW Mediterranean). The assemblage was monitored on 4 macroalgae: Corallina elongata (Rhodophyceae), Dictyota dichotoma, Dilophus fasciola and Halopteris scoparia (Phaeophyceae). The dominant dinoflagellates were Ostreopsis sp., and the accompanying species were Coolia monotis and Prorocentrum lima. The diatom Coscinodiscus sp. was an abundant component of the assemblage. Ostreopsis followed the same seasonal pattern on the 4 macroalgae selected. Substrate was not significantly different for the dinoflagellate assemblages. Ostreopsis was present both in the water column and in the sand concomitant with maximal cell densities on macroalgae. Small-scale sampling revealed that all the epiphytic organisms prefer slightly shaken habitats. While Ostreopsis sp. prefers shaken to slightly shaken waters, Coolia monotis prefers slightly shaken to calm ones. The dinoflagellate assemblage follows a clear seasonal pattern, achieving maximum cell concentration during spring and summer without significant relative changes in the species composition. The epiphytic assemblage was widespread along the Catalan coast and Majorca, although dinoflagellates were found to be more abundant in the Costa Brava. In Corsica, diatoms dominated the assemblage, whereas Ostreopsis sp. was a minor component. KEY WORDS: Ostreopsis · Coolia monotis · Prorocentrum lima · Benthic dinoflagellates · Ciguatera fish poisoningResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 26: 51-60, 2001 between sites (Tindall & Morton 1998). The mixed association of toxic dinoflagellates may contribute to the polymorphism of the clinical features of ciguatera (Yasumoto et al. 1987).Ostreopsidaceae species are widespread in most epiphytic and benthic dinoflagellate communities from ciguatera-endemic regions of the world (35°N to 35°S). Thus, the geographic distribution of Ostreopsis siamensis, O. lenticularis and O. ovata is similar to that of Gambierdiscus toxicus (Tindall & Morton 1998), with 2 notable exceptions: O. siamensis and O. ovata have been reported in the Mediterranean Sea (Taylor 1979, Tognetto et al. 1995. Nevertheless, data are limited on the incidence of Ostreopsis in the waters of the Mediterranean Sea and on the magnitude of potentially toxic epiphytic dinoflagellate assemblage attached to macroalgae.In this study, we quantified epiphytic dinoflagellate assemblages on the Catalan coast, NW Mediterranean. The potentially toxic epiphytic dinoflagellate assemblage associated with macroalgae was examined during an annual cycle in a rocky habitat. In addition, small-scale spatial variability and middle-scale spatial distribution were analysed to shed some light on the epiphytic dinoflagellate assemblages in the NW Mediterranean.The dominant dinoflagellate Ostreopsis sp. could not be assigned to any described species. Thus, a brief description of t...

Harmful benthic microalgae blooms represent an emergent phenomenon in temperate zones, causing health, ecological and economic concern. The main goal of this work was to compile records of Ostreopsis at large temporal and spatial scales, in order to study the relationship between cell abundances, the periodicity and intensity of the blooms and the role of sea water temperature in 14 Spanish, French, Monegasque and Italian sites located along the northern limits of the Mediterranean Sea. General trends were observed in the two considered basins: the north-western Mediterranean Sea, in which higher cell abundances were mostly recorded in mid-summer (end of July), and the northern Adriatic Sea where they occur in early fall (end of September). The sea-water temperature does not seem to be a primary driver, and the maximal abundance periods were site and year specific. Such results represent an important step in the understanding of harmful benthic microalgae blooms in temperate areas, and provide a good base for policy makers and managers in the attempt to monitor and forecast benthic harmful microalgae blooms.

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