Search

Over large areas of the Brazilian continental shelf, coralline algal rhodoliths provide habitats with high community diversity. In order to understand the role of rhodoliths in structuring the poorly studied infauna of these habitats, we determined seasonal patterns of their size and shape related to the associated biota, and experimentally tested the influence of living substrata in the Abrolhos Archipelago marine protected area. Samples (n = 20) were randomly collected from a rhodolith bed using cores (~1.7 L) during three seasons of the year. Subsamples were sorted by grain size, dry weight, degree of thallus branching, and associated invertebrate taxa. Live and dead rhodoliths with invertebrates removed and control samples with invertebrates present (n = 6) were transplanted inside baskets into the bed to test substrate associations. Transplanted samples were compared with natural ones directly collected from the rhodolith bed after nearly three months. The most common rhodolith-forming species was Mesophyllum erubescens. Polychaetes were usually the dominant taxon, making up 63% of the total infauna. The most common infaunal species was the polychaete Exogone dispar. There was a general seasonal trend of a reduction in invertebrate abundance from autumn/winter to spring. Amphipods were dominant in autumn (70% of sample) but half as abundant in winter and spring when their population density was similar to that of polychaetes (49%). Ophiuroids and molluscs were less abundant (up to 1% and 5% of the total sample). Polychaete abundance was significantly lower in live than in dead transplanted rhodoliths, whereas amphipods showed no difference. Variation in infaunal abundances was related to variability in habitat heterogeneity due to changes in rhodolith size and shape resulting from changes in water turbulence. The calcareous thalli of rhodoliths not only build complex calcareous gravels but also affect community diversity providing a refuge for infaunal groups. [ABSTRACT FROM AUTHOR]

Some species of sea urchins feature large variation in pigmentation. This variability may be the result of phenotypic plasticity or it may be associated with genetic divergence between morphs. Paracentrotus gaimardi exhibits five colour morphs (pink, brown, green, grey and black), which often occur side by side on the same rock. We studied genetic divergence between these morphs in three populations on the coast of Brazil. A fragment of the region encoding the mitochondrial ATPase 8 and 6 mitochondrial genes, a fragment of the intron of a nuclear histone and the entire nuclear gene coding for the sperm protein bindin were analysed. Mitochondrial DNA was differentiated between the pink and all other morphs, but the histone intron was similar in all colour morphs. In bindin, nine codons were found to be under positive selection and significant differences of allelic frequencies were observed in almost all pairwise comparisons between colour morphs. Although the molecular differentiation in bindin is not large enough to suggest reproductive isolation, some degree of assortative mating within morphs seems to be occurring in this species.