BackgroundThe rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin.Methodology/Principal FindingsSatellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles.Conclusions/SignificanceThermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.
In November 1984, non-treated Prudhoe Bay crude oil and dispersed Prudhoe Bay crude oil were intentionally released into two separate sites, representative of near shore mangrove, seagrass and coral ecosystems, as part of the TRopical Oil Pollution Investigations in Coastal Systems (TROPICS) field study in Bahia de Almirante, Panama. Data on the relative effects of non-treated crude oil and dispersed crude oil on these ecosystems (compared to a reference site) were acquired and analyzed over various periods (30 days, 3 months, and 2.6, 10, 17, 18, and 20 years). In the short term, the oil caused mortality to invertebrate fauna, seagrass beds, and corals at both sites. At the non-treated crude oil site, there was also significant mortality to the mangrove forest. Twenty-year observations and mangrove substrate core samples reveal the continued presence of oil and diminished mangrove repopulation, as well as substrate erosion, at the non-treated crude oil site. No oil was detected and no long-term impacts were observed at the dispersed crude oil and reference sites. These results provide baseline scientific data for developing a Net Environmental Benefit Analysis (NEBA) of dispersant use in nearshore tropical systems. This paper is a review of TROPICS data and its application to NEBA preparation. Data and NEBA from the 20-year TROPICS study clearly show that the use of dispersant in the near shore environment is a sound strategy for both minimizing environmental damage to tropical ecosystems and for providing the best opportunity for recovery and repopulation in this environment. Results of this work should be applicable to similar tropical ecosystems.
The salt marshes on the Brittany coast of France have undergone a number of changes and have been influenced by man-made and natural factors since the Amoco Cadiz spill of March 1978. This work catalogs the ecological changes which have occurred over the past eight years and presents original data on the present state of these marshes. The recovery of Brittany coastal marshes began following cleanup operations which were often damaging to marsh and marsh substrate. The physical and toxicological properties of the oil also were damaging in the short term, especially to annual species. Natural recovery began primarily by invasion of exposed areas with annuals and rhizome spreading of perennials. Within four years, an almost logarithmic recruitment process was begun by annuals followed by perennials. Pioneer and opportunistic species increased, facilitated by partially vegetated substrates available for seed and seedling retention and by increased seed and rhizome production. Man-induced restoration was also important and was done largely by planting wild or cultured stock. The final stage of marsh recovery, as existing today, is the emergence of perennial species of high and low marsh at elevations and tidal exposures typical for their growth. These successional changes in a marsh following a major oil spill (and various other man-made impacts) provide an understanding of the complex processes involved in marsh recovery. This understanding allows the formulation of planning guidelines to predict the long-term impacts of future incidents and to make proper recommendations for cleanup and restoration to aid the recovery process.
Oil spills occurring in freshwater (and upper estuarine) environments produce different effects than similar spills in marine environments, and thus require different considerations in protection and cleanup. Freshwater spills are primarily land- or river-based, and retention time of the oil in the environment takes one of two extremes, either very brief or very long. As in the marine environment, spills in marshes (predominantly grasses and sedges) are generally most destructive, especially when marshes have little or no flushing. The return of the marsh to a natural state is dependent upon the amount and type of oil, the amount of flushing, the type of vegetation, the type of cleanup, and the potential for natural revegetation (recovery). Spills in swamps (predominantly shrubs and trees) are influenced by similar factors and by the amount and type of understory vegetation. Spills occurring in marsh and swamp habitats in rivers are much less destructive and frequently result in oiling of the outer fringing vegetation rather than pooling or oiling of interior vegetation. Case studies of spills on the Cape Fear (North Carolina), Columbia (Washington), and St. Lawrence (New York) Rivers and in southern swamps (Louisiana and Texas) are given as examples of some points concerning freshwater spills. International examples are given by considering Nigeria and other countries. Suggestions for protection and cleanup are developed from these case studies.
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