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.

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Abstract:The community structure of most Caribbean reefs has changed dramatically since the 1980s. Invoking a chemistry analogy, in 1994 Hughes termed the change a "phase shift" to describe the change from a coral dominated habitat to one dominated by macroalga on the north coast of Jamaica over a period of 17 years. The loss of live coral cover is exemplified by the demise of Acropora spp. in Discovery Bay, Jamaica. Dense, monospecific high relief thickets of Acropora palmata (elkhorn coral) and A. cervicornis

SynopsisUsing a 3 m beam trawl, catch variation in the fish and prawn assemblage of the Labu estuary, Papua New Guinea was investigated during July and December 1981 and September 1984. About six times more organisms, three and a half times the biomass and twice as many species were caught per trawl at night than during the day. The greatest number of species, individuals and biomass were caught just after dusk. With the exception of Secutor ruconius, there was no significant difference in the catches trawled at ebbing and flooding tides. Over twice as many individuals of S. ruconius were caught during ebbing tides. Alignment of trawl direction in relation to the tidal current did not have a significant effect on the fish catch, but affected the prawn (Metapenaeus demani) catch. It is postulated that most species are not carried to and fro by tidal currents, but maintain their position in the estuary with respect to the substratum. Only prawns appeared to be carried by the currents. This study indicates that the most representative trawl results in terms of species diversity and abundance in shallow estuaries may be obtained at night and, that in estuaries with a small tidal range, tidal direction and velocity have 'little influence on catch. It also indicates that analyses of demersal nekton assemblages from daytime only estuarine trawl surveys must be approached with caution.