Seasonal changes of benthic and epiphytic dinoflagellates in the Veracruz reef zone, Gulf of Mexico

Benthic/epiphytic dinoflagellates were monitored every 2 wk from May to December 2005 in the Veracruz reef zone, Gulf of Mexico. This assemblage was characterized by low species diversity (at least 17 species from 11 genera) and high abundance: Amphidinium cf. carterae (41 172 cells g -1 substrate wet weight), Prorocentrum lima (29 756 cells g -1 ), Coolia monotis (2724 cells g -1 ), Ostreopsis heptagona (1202 cells g -1 ); P. lima was the dominant species. Clear sea- sonal population dynamics occurred, with the highest abundance in May-June, and the dynamics differed at 2 neighbouring sampling sites. In August to December dinoflagellate abundance de- creased considerably. Most of the epiphytic dinoflagellates did not show any significant preference for a macrophyte substrate (23 macroalgal and 2 seagrass species) or for any species or major algal group, although the seagrass Thalassia testudinum appeared to be the most abundant and perma- nent host species. The highest abundance of P. lima occurred on the chlorophyte Ulva fasciata (30 879 cells g -1 ) and T. testudinum (31 467). Dinoflagellates were usually scarce on dead coral (Acro- pora sp. and Millepora alcicornis) fragments (0 to 5039 cells g -1 ) and surface bottom sediments (2 to 84), and were slightly more abundant on living Diploria strigosa (329 to 1830) and more numerous in a fringing reef zone compared to a reef lagoon near an offshore island. Dinoflagellate abundance was not correlated with any measured physical or chemical parameter (temperature, salinity, pH, dis- solved oxygen, nitrates, nitrites, ammonium, phosphates, precipitation or wind speed and direction). There is a high potential for outbreaks of ciguatera in the studied area.