Scientific research needs The scope of work needed to address the issue of ecosystem consequcnces of biodiversity in coral reefs is, in broad terms, similar to that identified for other marine ecosystems (Butman and Carlton 1993): (I) research on the determinants of species distribution and abundance, and (2) biology and ecology of species that play a pivotal role in the maintenance and generation of diversity as it relates to community and ecosystem function and stability.
As in other ecosystems, the success of crucial aspects of this work will rely on improvement and expansion in several related areas which are currently deficient. For example, there are still many reef groups and locations for which taxonomic treatises arc unavailable or sub-standard, and there remain fundamental questions regarding the distinctions between species. These questions - which are germane to the assessment and monitoring of species diversity and the analysis of its origins, as well as its implications for ecosystem function - can now be approached using genctic probes unavailable only a few years ago. All are aspects which are integral to the DIVER-SITAS program concerned with the broader issues of biodiversity throughout the biosphere (Grassle et ai. 5990; di Castri and Younes 1996).
Coral reefs provide a number of challenges and opportunities in addressing this scope of research. For both individuals and for multidisciplinary collaborations within and among institutions and countries, they include a combination of comparative and experimental approaches:
• experimental reduction of diversity of some reef areas over a period of time while monitoring structure, dynamics and ecosystem processes of the simplified and control (unmodified) systems;
• comparative studies of these types on "pristine" reefs and reefs of the same type in the same region which have already been subjected to natural or unplanned perturbations which have resulted in reduced diversity;
• comparative studies on reefs with strong natural differences in biodiversity due to their geographic locations and environmental settings;
• "a cross-biome experiment" in which, in the manner of the Hubbard Brook experiment (Borman and Likens 1979), terrestrial scientists investigate various aspects of catchment transformation under management, and marine scientists investigate the consequences for populations, communities and processes in adjacent estuaries, coastal waters and reefs.
Applications to management of coral reefs The basic issue for management is to discriminate between human impact, which can be managed, and the natural variation of ecosystems. The ecological structure and function of a coral reef in any particular location will be the result of the long-term (over geologic time) interplay between natural factors upon which (in recent time) human impact has been superimposed. Inter-disciplinary studies conducted over the full range of regional development of reefs and encompassing the time scale of ocean processes will provide the best opportunity to identify thresholds and rates of responses of reefs to global change, and to evaluate the success of our attempts to manage them for sustainable use. Study of the Quaternary history of fossil coral reefs, like those undertaken on Quaternary vegetation patterns, may also shed light on the natural responses of reef ecosystems to perturbations at local (tectonic) and global (sea level and climate fluctuation) scales.
Application of research findings to management objectives aimed at sustaining proper ecosystem function and services will require a quantitative and predictive understanding of many of the issues raised in this chapter. Quantitative studies are needed to understand: the real threats posed by terrestrial input in specific contexts (e.g. the extent of the influence of Hallock and Schlager's (1986) "nutrient halo" at river mouths under conditions of flood and low flow); mechanisms and thresholds leading to state changes and wide population fluctuations in "faciiitator"popu!ations (Done 1992a; Knowlton 1992); the domains of water quality, hydrodynamics and grazing pressure that maintain certain reef states, and the areas over which such domains exist. Additional efforts should also be directed toward elucidating patterns of hydrodynamic closure, reef interconnectedness and population replenishment. Ecological models are needed to predict the responses of coral reefs under different scenarios of growth in human populations, urbanization, industry and agriculture, and under different regimes of management.
The need for international collaboration There are strong practical arguments for strengthening international collaboration and communication among reef scientists, oceanographers and terrestrial researchers. Extreme pressure on coral reef biodiversity and function already exists on coral reefs in many parts of the world. However, the natural replenishment of the depleted reef resources in one country may rely on the reproductive output of reefs in another, and the conditions for maintenance of biodiversity and ecosystem function may be strongly influenced by land use practices and runoff. Thus individual reefs cannot be either managed or understood in isolation from other reefs, or from adjacent marine or terrestrial habitats. For these reasons, existing intergovernmental arrangements, including those among developing tropical countries where most coral reefs occur, and between developing and developed nations should be supported and strengthened. Networks of marine laboratories are a readily available infrastructure to carry out synoptic, standardized protocols of observations on the structure and function of coral reefs within coastal zones. The network is a powerful tool for the development of meso-scale remote sensing of the coastal zone, particularly land-sea interactions, interplay of coastal and oceanic processes, and regional patterns of marine biological diversity. The CARICOMP network of Carribean marine research laboratories, parks and reserves (Ogden 1987) is one such arrangement which links nations bordering the Caribbean sea. This network provides a useful model for information sharing, cooperation and coordination among coral-reef scientists.
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