diversity

Abstract:

Understanding the patterns and processes that govern the functional structuring of communities along spatial scales is still a challenge in community ecology. Functional diversity is the result of the action of abiotic and biotic filters that regulate the presence and contribution of functional attributes inside the assemblages. Large-scale studies demonstrate that reef fish fauna has a high degree of functional redundancy, where the addition of species does not normally result in new functions in local assemblages. However, niche theory predicts that species tend not to overlap in resource use, a pattern that can be exacerbated at small scales. In this context, the aim of this study is to investigate how the functional structure of reef fish assemblages respond to area increase in three locations in the western Atlantic Ocean subject to a wide gradient of species richness: Curaçao, Abrolhos and Atol das Rocas. More specifically, the relationships between the indices of functional richness (FRic), functional evenness (FEve) and area were evaluated. Based on niche theories and efficient use of resources, we hypothesized that as area increases, new niches become available, and therefore new species are sampled. Likewise, it is expected that functional richness will increase as the sample area increases. On the other hand, evenness may decrease, since larger areas can accommodate more functionally similar species and concentrate greater accumulations of functional entities in certain areas of the functional space, decreasing the FEve. For this purpose, species occurrence data were gathered from checklists and occurrence and abundance data from 40 m² visual censuses. Species were classified into eight functional attributes. For each metric, FRic and FEve accumulation curves were constructed using an extension of the Gower dissimilarity matrix and Principal Coordinate Analysis (PCoA). Functional indices were calculated from randomization of sample units (visual censuses) and contrasted with null models. We found that increases in the sample area lead to an increase of FRic and a decline of FEve, regardless of local species richness. Also, small sample areas are characterized by high FEve (i.e., functional entities are more evenly distributed in the functional space). Regardless of the species richness, the functional spaces are relatively similar between the three locations, suggesting that even isolated reefs have communities that present a minimal functional structure to maintain the functioning of the ecosystem. These patterns may be related to the optimization of resource use in isolated and poorly connected areas, a mechanism to reduce local competition. The combination of limiting similarity and the best use of available resources result in a high functional equitability ? when the functional entities are more evenly distributed in space. These processes, therefore, may have shaped the functional structure of communities in isolated reef systems sampled.

https://repositorio.ufsc.br/handle/123456789/242634

With the SCUBA diving industry growing at a reate of 7% per annum and a major qualifying agency havig just certified its 10 millionth diver, an increasing amount of direct pressure is being placed on marine organisms. In many tropical areas, diving tourism is concentrated in a small area and is often seen to be having an impact on bethic organisms....This study looks in detail at the role of SCUBA activity in coral divesrity maintenenace, and assesses its significace as a disturbance to the reefs of Bonaire

Seagrasses, marine flowering plants, are widely distributed along temperate and tropical coastlines of the world. Seagrasses have key ecological roles in coastal ecosystems and can form extensive meadows supporting high biodiversity. The global species diversity of seagrasses is low (b60 species), but species can have ranges that extend for thousands of kilometers of coastline. Seagrass bioregions are defined here, based on species assemblages, species distributional ranges, and tropical and temperate influences. Six global bioregions are presented: four temperate and two tropical. The temperate bioregions include the Temperate North Atlantic, the Temperate North Pacific, the Mediterranean, and the Temperate Southern Oceans. The Temperate North Atlantic has low seagrass diversity, the major species being Zostera marina, typically occurring in estuaries and lagoons. The Temperate North Pacific has high seagrass diversity with Zostera spp. in estuaries and lagoons as well as Phyllospadix spp. in the surf zone. The Mediterranean region has clear water with vast meadows of moderate diversity of both temperate and tropical seagrasses, dominated by deep-growing Posidonia oceanica. The Temperate Southern Oceans bioregion includes the temperate southern coastlines of Australia, Africa and South America. Extensive meadows of low-to-high diversity temperate seagrasses are found in this bioregion, dominated by various species of Posidonia and Zostera. The tropical bioregions are the Tropical Atlantic and the Tropical Indo-Pacific, both supporting mega-herbivore grazers, including sea turtles and sirenia. The Tropical Atlantic bioregion has clear water with a high diversity of seagrasses on reefs and shallow banks, dominated by Thalassia testudinum. The vast Tropical Indo-Pacific has the highest seagrass diversity in the world, with as many as 14 species growing together on reef flats although seagrasses also occur in very deep waters. The global distribution of seagrass genera is remarkably consistent north and south of the equator; the northern and southern hemispheres share ten seagrass genera and only have one unique genus each. Some genera are much more speciose than others, with the genus Halophila having the most seagrass species. There are roughly the same number of temperate and tropical seagrass genera as well as species. The most widely distributed seagrass is Ruppia maritima, which occurs in tropical and temperate zones in a wide variety of habitats. Seagrass bioregions at the scale of ocean basins are identified based on species distributions which are supported by genetic patterns of diversity. Seagrass bioregions provide a useful framework for interpreting ecological, physiological and genetic results collected in specific locations or from particular species. © 2007 Elsevier B.V. All rights reserved.