Reefs

Seagrass meadows cover about 0.05-0.15% of the world’s ocean and are some of the most productive systems on Earth. Direct and indirect human-derived impacts have led to significant seagrass declines worldwide and the alteration of services linked to their biodiversity. Effective conservation and the provision of sustainable recovery goals for ecologically significant species, such as green turtles (Chelonia mydas), are limited by the absence of reliable information on seagrass extent. This is especially true for the Wider Caribbean Region (WCR) where many conservation initiatives are under way, but impaired by the lack of accurate baseline habitat maps. To assist with such a fundamental conservation need using high resolution remote sensing data, both environmental and methodological challenges need to be tackled. First, the diversity of environments, the heterogeneity of habitats, and the vast extent of the targeted region mean that local expertise and field data are seldom available. Second, large-scale high-resolution mapping requires several hundred Landsat 5 and 7 images, which poses substantial processing problems. The main goal of this study was to test the feasibility of achieving Landsatbased large-scale seagrass mapping with limited ground-truth data and acceptable accuracies. We used the following combination of methods to map seagrasses throughout the WCR: geomorphological segmentation, contextual editing, and supervised classifications. A total of 40 Landsat scenes (path-row) were processed. Three major classes were derived (“dense seagrass”, “medium-sparse seagrass”, and a generic “other” class). Products’ accuracies were assessed against (i) selected in situ data; (ii) patterns detectable with very high-resolution IKONOS images; and (iii) published habitat maps with documented accuracies. Despite variable overall classification accuracies (45-85%), the resulting thematic maps were deemed acceptable to (i) regionally provide, following their critical evaluation, an adequate baseline for further large-scale conservation programs and research actions; and (ii) regionally re-assess carrying capacity estimates for green turtles. They certainly should represent a drastic improvement relative to current regional databases.

The number of no-take marine protected areas (here referred to as no-take areas, NTAs) on coral reefs has increased considerably in recent decades. Coincident with accelerating degradation of coral reefs, expectations of the benefits that NTAs can provide for coastal societies and sustainability of marine ecosystems has grown. These include increasing abundance of reef organisms both inside and outside NTAs, protecting key ecosystem functions, and providing social and economic benefits through improved ...

Uranium (U) pollution of the surface water and groundwater of the Wonderfonteinspruit (WFS) catchment caused by gold mining over more than a century has been an ongoing concern for several decades. Triggered by a recent increase in media attention, political pressure on governmental authorities has mounted to assess the associated health risks and implement appropriate mitigation measures. However, owing to the complexity of the catchment arising from the presence of a multitude of dischargers, a complex karst hydrology and large-scale modifications thereof by deep-level gold mining, most attempts to address the issue to date have been limited to uncoordinated ad hoc studies generally suffering from a lack of temporal and spatial representivity of the underlying data. Part 2 of a series of 2 papers aimed at quantifying the extent of mining-related U pollution in the WFS catchment, this paper addresses the pollution of surface water, groundwater, as well as mine effluent. Based on cl...

Even though mining-related uranium (U) pollution in the Wonderfonteinspruit (WFS) has been an ongoing concern since the mid-1960s, media attention has increased considerably recently, focusing on pollution-related health risks that unsettle the general public. In view of recent findings that U might be more toxic than previously thought, such concerns need to be addressed. This even more so as South Africa has embarked on a nuclear expansion programme aimed at, amongst others, extending mining and processing of U. This is Part 1 of a series of papers aimed at the quantification of the extent of U pollution in the WFS, in order to provide a factual base for subsequent risk assessments. This paper provides an overview of recent findings on U toxicity with specific reference to drinking water, together with a critical examination of related international and South African guidelines. Based on a brief description of the study area and the impacts of mining over the past decades, the ori...

ABSTRACT Several factors have contributed to the continuing degradation of reefs worldwide. However, local anthropogenic threats are the most serious and lasting causes for the devastation of coral reefs. The ecological relationship between biomes and anthromes provide us an interesting field of current studies. In Guarajuba Beach at the northern coast of Bahia there is a reefs complex which has been studied since the 80s. These reefs are suffering modifications due to the installation and continuous expansion of a tourist residential complex. Therefore it is an interesting study subject of the relation between biomes and anthromes represented here by coral reefs and urban occupation. Our main objective is to initiate the evaluation of urbanization effects on the coral reefs in Guarajuba Beach, based on the study of the urbanization process with the support of historical series of air images and sediment composition analysis, comparing them with results obtained before the occupation process. In these studies the sediment composition does not show big differences from those observed by Nolasco (1987); however there is a displacement towards the front of the reef, which is considered as an urbanization effect, as well as the destruction of dune areas and salt marshes nearby. On account of this process the concentration of organic fragments, which indicates reef origin predominance, appear displaced towards the ocean when compared to that observed in 1987 profiles.