Biodiversity of Coral Reefs: What are We Losing and Why?

SYNOPSIS. Coral reefs are threatened by numerous anthropogenicimpacts, some of which have already had major effects worldwide.These unique tropical environments harbor a high diversity ofcorals, reef invertebrates, fish and other animals and plants.In most taxa, the species diversity of reef-associated organismsis poorly understood because many of the species have yet tobe collected and described. High coral mortality has been associatedwith natural events such as hurricanes, predator outbreaks andperiods of high temperature, but has also resulted from excessnutrients in sewage and from specific pollutants. Reef coralsand associated organisms are also threatened by the possibilityof global warming which will result in rising sea levels andperiods of increased temperature stress, and which may alsobring increased storm frequency and intensity. Although therecent extensive episodes of coral bleaching in the Caribbeanand eastern Pacific cannot be causally related to global warmingat this time, the close link between bleaching and temperaturesuggests that global warming will result in severe changes incoral assemblages. Major reef destruction has followed outbreaksof the predatory seastar Acanthaster planci in the Pacific.Although this is considered part of a natural disturbance cycle,there are indications that altered land use patterns and reductionof predators on this seastar by human activities may have increasedthe severity of outbreaks. Recreational and commercial use ofreefs has also increased, and has caused extensive damage, especiallynear areas of high population density. One of the most obviousand widespread losses to reef biota is the reduction in fishpopulations from intense overfishing in most reef areas of theworld. Coasts without adequately managed reefs have sufferedintense overfishing for both local and export purposes, to thepoint where the positive effects of fish on those reefs havebeen compromised. The combination of these destructive factorshas altered reefs in all localities, and many that were onceconsidered protected by distance and low population densityare now being exploited as well. On the positive side, improvedunderstanding of ecological processes on reefs combined withconcerted conservation efforts have managed to protect someextensive areas of reef for the future.     

The Energetics of Asexual Reproduction and Colony Formation in Benthic Marine Invertebrates

There are several formsof individual and colon) organizationavailable to benthic marine invertebrates with indeterminategrowth In particular anthozoan coelenterates exhibit three suchforms of organization 1 solitary individuals without asexualreproduction 2 colonies or clonal groups with determinate polypsize and indeterminate colony size and 3 colonies or clonalgroups with both indeterminate polyp size and indeterminatecolonyor clone size The last group includes species where asexualreproduction is continuous and those where it is limited toa single season of the year A model is presented which definesthree optimal sizes for indeterminately growing organisms 1optimal size for a solitary individual 2 optimal size of a polypwithin a colony and 3 optimal size at asexual division The optimaare derived by maximizing the difference between energy intakeand energetic cost Simulations allow prey size and habitat qualityto vary and derive predictions of optimal size and organizationfor each case Individual and clonal growth rates are modelledfor the case where asexual reproduction is limited to a singleseason and poly p sizes within clones are compared The modelpredicts that the three torms of organization among anthozoanpolyps are related primarily to the size distribution of prey