Ramifications For Coral Reef Ecosystems And People In A Rapidly Changing Climate

The key question for coral reef ecologists is how changes in the abundance of reef-building corals will affect those thousands of other species that are totally dependent on the coral framework for food, shelter and reproduction (Fig. 10.5). While defining the full set of relationships between corals and other reef organisms goes beyond the space allowed here, it is important to outline some of the ways that the highly interconnected coral reef ecosystem are likely to be affected by climate change.

Several studies have now demonstrated that impacts of coral bleaching and mortality on reef fish populations include local extinctions, reduced taxonomic distinc-tiveness and species richness, and a loss of species within key functional groups. Several studies reveal that fish diversity is directly affected by the loss of corals. Using data from Pacific and Indian Ocean studies, it is clear that fish populations appear highly sensitive to changes in coral cover, with 62% of fish species declining in abundance within three years of disturbances that resulted in greater than a 10% decrease in coral cover. Particular species appear to be more sensitive than others, with coralivorous (coral eating) species being the most sensitive. The response of other less coral dependent reef fish is not clear. Several studies have shown that the number of herbivorous fish may increase after the coral mortalities associated with mass bleaching events, primarily due to the increase in algal turfs, which are the preferred food of these fish species.

Our current understanding of how coral reef organisms other than fish are influenced by the loss of corals from reefs is limited. It is clear that other organisms are equally susceptible to the projected changes in coral cover. Obligate crab fauna that live in corals (such as Pocillopora spp., for example) disappear from corals that have

Figure 10.5 The effect of changing global conditions has ramifications on reef-building corals and on the organisms that live in association with coral reefs. The increasing mortality of corals leads to a loss of reef function and services, which leads to reduced biodiversity and effects on fish populations, among other things. These changes have ramification for the humans dependent on coral reefs through effects on tourism, resources for coastal populations and protection of coastal infrastructure from storms. Maintaining reef resilience through protection of herbivore populations is one possible way to improve the recovery of coral reefs after coral bleaching. It is important to understand that increasing uncertainty does not mean that the problem does not exist. Rather it highlights the fact that we know things will change but have little detailed information on the nature of the changes or their magnitude. (Figure: D. Kleine and O. Hoegh-Guldberg.)

Figure 10.5 The effect of changing global conditions has ramifications on reef-building corals and on the organisms that live in association with coral reefs. The increasing mortality of corals leads to a loss of reef function and services, which leads to reduced biodiversity and effects on fish populations, among other things. These changes have ramification for the humans dependent on coral reefs through effects on tourism, resources for coastal populations and protection of coastal infrastructure from storms. Maintaining reef resilience through protection of herbivore populations is one possible way to improve the recovery of coral reefs after coral bleaching. It is important to understand that increasing uncertainty does not mean that the problem does not exist. Rather it highlights the fact that we know things will change but have little detailed information on the nature of the changes or their magnitude. (Figure: D. Kleine and O. Hoegh-Guldberg.)

bleached or die. Many other species form tight relationships with corals and hence are likely to be lost from coral reefs as coral abundance declines. There may also be an important density threshold in which some coral dwelling species require their coral colonies to be clustered closely so that they can access mates for reproduction.

The changes that are set to occur on coral reefs will also affect humans with direct and indirect dependence on them. This topic is clearly important and deserves considerably more space than a concluding paragraph (Fig. 10.5). Australia's coral reefs are currently an important economic engine for its communities and coastal economies, generating over $6 billion per annum from GBR tourism alone. Great Barrier Reef tourism is highly dependent on its key competitive advantage of having the reputation of being the most pristine coral reef on the planet. This reputation allows the Australian tourism sector to compete with other tourist destinations in South-East Asia, the western Indian Ocean and the Caribbean that are closer to most international tourist domiciles in terms of travel time. Analysis of the potential effect of loosing that competitive edge through the deterioration of coral reefs on the Great Barrier Reef through climate change indicates that the costs could be significant. Estimated impacts vary depending on market characteristics and factors such as international trends and politics, but if one uses the proportion of the income that is due to people coming to Australia to see our Great Barrier Reef, it is clear that climate driven reef degradation could potentially reduce international tourist income by as much as $8 billion over the next two decades.

Reefs also have major importance to people in developing countries, with over 100 million people subsisting on coral reefs as a source of food. While the details of the socio-economic impacts from climate change will vary, countries like Indonesia, Fiji and other Indo-Pacific countries could all potentially face declining coastal resources. This decline would have flow-on consequences resulting from the need to find alternative livelihoods for the many millions of people that live in coastal zones in Asia and the Indo-Pacific. Understanding the economic and social ramifications of climate change on coral reefs will consequently be critical for preparing people, industries and governments for the changes that seem almost certain to occur over the next 50 years.

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