COMMUNITY STRUCTURE OF INFRALITTORAL MACROALGAE OF THE EXPOSED SIDE OF CABO FRIO ISLAND (RIO DE JANEIRO, BRAZIL)

Abstract

An infralittoral community dominated by benthic macroalgae was studied on the external side of the Cabo Frio Island in Arraial do Cabo (Rio de Janeiro State). For the present study, phytosociological methods‚ rarely used in Brazil, were employed. The collected samples, referred to as “parcelas”, correspond to the total sampling of a given area, along with the substratum, and phytosociological parameters (e.g. number total of species) and field information (e.g. depth, wave movement etc.). For most of the studied depths and areas, the community proved composed of different strata: a crustose erect one forming a canopy, an arbustive one with several entangled species, and one or two epiphyte strata are formed between the canopy algae. This work allowed to identify a continuum which reflects on its extremes two different and very distinct associations: a Pterocladiella capillacea-Cheilosporum sagittatum association, which characterizes the rocks of the shallowest areas. The ecological groups taking part in it are mainly photophilous infralittoral algae under strong wave action and infralittoral epiphytes, and not the sciaphilous groups as suspected initially. The characteristic species (mosr predominant but not exclusive) of that association are Pterocladiella capillacea, Cheilosporum sagittatum, Arthrocardia flabellata, A. gardneri, Ceramium tenerrimum, Ulva rigida, and Protectocarpus speciosus. The other association, Acrosorium uncinatum-Rhodymenia delicatula (?), is composed by the typical ecological groups of sciaphilous biotopes. Algae belonging to this association have shorter thalluses, live under weak sunlight and are not under strong wave action. Characteristic species of this association were: Acrosorium uncinatum, Callophyllis microdonta, Peyssonnelia capensis, Plocamium brasiliense, Ceramium comptum, Rhodymenia delicatula (?), Ulvella lens and Dictyota menstrualis.