Millepora alcicornis (Cnidaria: Hydrozoa) as substrate for benthic fauna

Abstract

Universidade Federal do Ceara - Departamento de Biologia (Bloco 906 Campus do Pici, 60455-760 Fortaleza, CE, Brasil) *E-mail: hmc@ufc.br More than half of the world´s species live inside or on other organisms, where they find conditions favorable to their growth (TOWNSEND et al., 2006) and the majority of hard substrata, including the coralline ones, are colonized by perforating and fouling organisms (ZUSCHIN et al., 2001). The living corals create a variety of habitats for a large number of species, giving support for sedentary organisms and food or shelter for mobile ones (REED; MIKKELSEN, 1987; DIAZ-CASTANEDA; ALMEDA-JAUREGUI, 1999). Many taxonomic groups are found associated with corals, including non-colonial organisms such as Crustacea, Mollusca, Polychaeta and Sipuncula, and colonial ones such as Porifera. Each colony forms a community whose members live in a close relationship, though to establish the limits between the diverse types of interactions is not always easy (DAJOZ, 2005). The purpose of this study is to test the hypothesis that the diversity and density of the macrofauna associated with live colonies of Millepora alcicornis is correlated with the volume of the colony in the “Area de Protecao Estadual dos Recifes de Coral (RN)” in Northeastern Brazil. The study area (Maracajau Reef) is located 5 km from the beach, being 9 km in length and 2 km in width, with depths that vary from 1 to 4 meters at low tide (FEITOSA et al., 2002). The waters of the area are warm (average 28oC) and calm during most the year (MMA, 2003). The samples were collected in July and November of 2004 and February of 2005, when 26 reefs where Millepora alcicornis colonies had been located were marked with buoys, by snorkeling. Later, by SCUBA diving, one colony of each reef was chosen randomly and samples were collected from it. The colonies were placed in plastic bags to prevent the loss of the vagile fauna and then extracted from the substratum with the aid of hammer and chisel. Later, the samples were fixed in 4% formalin solution for 24 hours. Each colony was examined, in the laboratory, for removal of the vagile epifauna. In order to measure the colonies´ respective volumes, they were placed in containers with a known volume of water. The colonies were carefully broken up, with hammer and chisel, and the animals carefully removed to prevent damage. The organisms found were preserved in 70% alcohol before sorting and identification. The macrofauna was analyzed with the use of Shannon-Weaner´s diversity (H'), Pielou´s equitability (J´) and Margalef‘s species richness indices, using the Primer 5 (Windows 5.2.4.) program. The density (ind./cm³), the number of individuals (n) and the number of species (s) were compared to the size of the colonies and the epifauna was compared with the infauna, by means of Spearman´s correlation coefficient (r), using the Statistical program (Windows 5.0). Ninety-five (95) non-colonial species and 1,234 organisms were found in association with Millepora alcicornis . Collected colonies had a volume that varied from 130 to 3146 cm³ (863 ± 647 cm³) and a density that varied from 0.01 to 0.27 ind./cm³ (0.07 ± 0.06 ind./cm³). The individuals (n) and species (s) numbers correlated significantly with the colony volume (p 0.05). The animals found in this study belonged to six taxa (Crustacea, Echinodermata, Mollusca, Nemertea, Polychaeta and Sipuncula. The non-colonial organisms found in association with Millepora alcicornis belonged mainly to the taxon Crustacea that occurred in 93% of the samples, followed by Polychaeta (76%), Mollusca (69%), Sipuncula (42%), Echinodermata (38%) and Nemertea (7%).