Branqueamento do coral escleractínio síderastrea stellata dos recifescosteiros da Paraíba e taxonomia e cultivo dos microssimbiontes associados.

Abstract

The main purpose of this work was to study the bleaching phenomenon and the seasonal changes of color patterns in colonies of Síderastrea stellata of the costal reefs of Picãozinho in the State of Paraíba, northeastern Brazil, from September, 2008 to May, 2009, as well as to characterize the seasonal cycle of the zooxanthellae hosted by health colonies of this scleractinian during this period. We also study the microsymbionts hosted by this coral species, emphasizing the taxonomy and culture of the diatoms (bacilariophyceans), in samples collected in the coastal reefs of Cabo Branco, João Pessoa, PB, in the years 2007, 2008, and 2009. For the study of the zooxanthellae the tissues of four healthy fragments of S. stellata collected during low tides were water picked and processed in the laboratory using a Fuchs—Rozenthal counting Chamber and an optical microscope. Unialgal cultures of epibiont diatoms hosted by S. Stellata were obtained by inoculating aliquots of the extracted coral tissue in culture media. The remaining material were submitted to the oxidation process for cleaning the diatoms frustules and mounted on permanent slides. Examinations of these materials were conducted in an optical microscope. Of the 560 colonies monitored was found healthy, pale, bleached, and purple colonies, with the highest frequency of pale colonies (445%) and the lowest for the purple colonies(5.4%). The data show that the bleaching and changes in color patterns seen in S. stellata are applicants on the reefs of Picãozinho, and these phenomena have destabilized the symbiotic association between corals and their zooxanthellae. It was found that more than one of the environmental variable studied affects the seasonal dynamics of the zooxanthellae of S. stellata, since these dinoflagellates exhibited distinct patterns of seasonal variation in terms of population density, mitotic index and cell diameter. We also demonstrate that S. stellata host a high diversity of epibiont diatoms. It was computed in the studied materials a total of 1.136 specimens of diatoms belonging to 39 genera with 28 species identified. The most frequent genera were Amphora, Cocconeis, Cyclotela, Díploneis, Grammatophora, Paralia, Navicula, Nitzschia, Synedra, Surirella and Trachyneis. Seasonal differences were found in diatoms assemblages, with the highest number of species recorded in the rainy season. The laboratory experiments performed with cultures of Cylindroteca closterium and Entomoneis alata has demonstrated a high growth potential of these species, which reached considerable densities in a few days of cultivation. The culture data and taxonomic results showed that the diatoms hosted by S. stellata are opportunistic; taking advantage of the nutritional conditions provided by the mucus secreted mucus the coral species. Laboratory data added to the taxonomic studies show that the epibionts of S. stellata are opportunistic, taking advantage of rapid nutritional conditions provided by the host available in the mucus secreted by it. Seasonal differences were observed in the population of these microorganisms when periods of drought and rainfall were analyzed, and in the dry season there was a considerable reduction in the number of species found attached to coral. These findings confirm the importance of symbionts as biological indicators of environmental quality. Understanding patterns of growth and maximum yield of diatoms isolated from cnidarians may bring new light to the ecology of the host, especially during periods of environmental perturbations.