SANTANA, J. K. S.; DA SILVA SANTANA, JORDANA KALINE; http://lattes.cnpq.br/2952313296363161; SANTANA, Jordana Kaline da Silva.
Resumen:
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.