Structure of the Macroalgal Community Associated with the Seagrass Halodule wrightii Ascherson in the Abrolhos Marine National Park, Brazil

Abstract

The Abrolhos region of Brazil is recognized for its ecological importance and richness of endemic species. Between Redonda and Siriba, two small islands in the Abrolhos archipelago, there are dense populations of macroalgae associated with seagrass (Halodule wrightii) beds. Samples of the community were collected by SCUBA divers in August and December 1995 and April 1996. Forty-nine taxa of macroalgae were found associated with the seagrass at the study site. Nine macroalgae were recorded for the first time for the Abrolhos National Marine Park and four taxa are reported for the first time for Bahia State. Macroalgae were found growing on dead corals and rocks, as epiphytes on incrusting calcareous algae (rhodoliths or maerls), as epiphytes on Udotea flabellum, episamic, or growing unattached. In terms of richness per substratum: unattached > on calcareous algae, epilithic or on Udotea > episamic. In terms of biomass per substratum: episamic > unattached > on Udotea > epilithic > on calcareous algae. No significant differences in richness were found between times, but macroalgal diversity and evenness were greater in August 1995 than at other times. The seagrass biomass did not vary seasonally but the seaweed biomass did. Seagrass was the largest component of macrophyte biomass in August 1995 and April 1996. However, in December 1995 macroalgal biomass was double that of the seagrass and was significantly higher than in August 1995. Rhodophyta was the richest division > Phaeophyta > Chlorophyta. The macroalgal community in the seagrass beds at Abrolhos was considered to be rich and diverse and contained a disproportionately high number of taxa of Phaeophyta (19 %), when compared to the whole Brazilian flora.