37 research outputs found
Seasonal influence of drifting seaweeds on the structure of fish assemblages on the eastern equatorial Brazilian coast
Abstract The present study compared fish assemblages in two adjacent areas, one with drifting algae (A) and another without it (WA), in order to assess seasonal changes in diversity and composition. Both areas were located in São Cristóvão beach, Rio Grande do Norte state, on the semi-arid North-Northeastern coast of Brazil. A total of 4988 individuals were caught, the most species-rich families being Scianidae, Ariidae, Engraulidae and Carangidae. Species richness and abundance were slightly higher in site A, but diversity and evenness were higher in site WA. However, with the exception of evenness, such differences were not significant at any time during the study. Species composition was also similar between the two sites over the year. Nevertheless, in spite of the similarities, seasonal changes of environmental conditions, particularly rainfall, seemed to influence fish assemblages differently in the two areas. This may have led to changes in assemblage structure, causing the differentiation of the communities in the dry season. The present study presents evidence that fish assemblages in habitats with and without drifting seaweeds are not static and may become more similar or different, depending on the environmental conditions, suggesting that there is a complex relationship between primary productivity, trophic level and the structure of fish assemblages
Looking at the soft-bottom around a coastal coral reef: the impact of terrigenous input on Polychaeta (Annelida) community
Abstract Erosion on coral reefs produces fragments of the constructor organisms that are scattered all around, thus enlarging the reef boundaries. Statistical modelling approach was used to investigate whether the Polychaeta community around Sebastião Gomes reef (Abrolhos Bank, Brazil) is influenced equally by sediment characteristics and/or by position related to the reef, that are variables related to the terrigenous input influence. In July 2007, a period dominated by winds that resuspend fine sediment from the land to coastal reefs, sediment samples were taken on four transects perpendicular to the reef (S, W, N and E) and a total of 121 species of polychaetes were recorded. The most abundant species was the carnivorous Goniadides carolinae and the model selected for it approximates to the best models fitted for both total macrofauna and polychaete abundance. These models represented higher abundance in coarse carbonate sediments on windward reef faces, where there is almost no terrigenous sediment. On the other hand, the Polychaeta richness did not depend on the transects. Sebastião Gomes reef is one of the many coastal reefs from Abrolhos Bank, whose healthy is probably in danger because of the increase of mud related to human activities, as deforestation and, recently, mining waste
On defining the “edge” of a seagrass bed
Need for a definition of the “edge” of a seagrass bed: The edge is the basis for: 1. Total acreage of seagrass. 2. Change detection, both by groundbased transects and mapping from aerial photos. 3. Seagrass restoration targets; assessments of progress may be based on a comparison of the deep edge of grass beds to the target depth