Dinoflagellate, Diversity and abundance in two Belizean Coral Reef-Mangrove Lagoons: A test of Margalefs Mandala

Abstract

Dinoflagellates are frequently abundant in the coral-reef mangrove lagoons off the coast of Belize. Margalef predicted that marine environments with low turbulence and high nutrient inputs would favor dinoflagellates. A long-term study of coral-reef mangrove embayment cays of Belize, including this study, has shown that these systems contain abundant dinoflagellate species. Consistent with Margalef’s prediction, these habitats are protected from wind mixing, show a high degree of stratification, and have restricted water exchange with surrounding oligotrophic waters of the open barrier-reef system. This limited water exchange favors retention of dinoflagellate cells and the trapping of nutrient rich organic material that is rapidly recycled providing a relatively high-nutrient environment. Species-specific blooms are a common feature of these systems. In the study, the ecology and diversity of dinoflagellate species from two nutrient-enriched habitats, Douglas Cay and The Lair at Twin Cay, were examined in detail. A comparison of the species composition from both sites showed that Douglas Cay contained coastal planktonic and offshore oceanic dinoflagellates while The Lair at Twin Cay contained mainly benthic dinoflagellates. A total of 19 bloom-forming species were observed in these systems during three two-week studies. The morphology of eight of these bloom-forming species is illustrated in Scanning Electron Microscopy (SEM) photographs. These include Bysmatrum caponii, Dinophysis caudata, Gonyaulax grindleyi, Peridinium quinquecorne, Gonyaulax polygramma, Gonyaulax spinifera, Lingulodinium polyedrum, and Pyrodinium bahamense var. bahamense. Approximately half of the bloom-forming dinoflagellates are known toxin producers. The congruence between Margalef’s prediction and the distribution of dinoflagellates in these naturally eutrophic systems suggests that increased nutrient inputs in oligotrohic portions of the Caribbean will favor a shift in species dominance toward dinoflagellate species. The effect will be most pronounced in bays or other regions where turbulence is likely to be reduced. This species shift may have consequences for food web dynamics and the prevalence of dinoflagellate toxins in the food chain. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 1 Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington D.C., 20560. 2 NOS/NOAA, Center for Coastal Fisheries Habitat Research, 101 Pivers Island Road, Beaufort, North Carolina, 28516. Manuscript received 29 July 2005; revised 22 August 2005.