C2.2.4 Impact of coral mortality on reef fisheries (Chapter 5, Box 5.4)
Coral reefs and their fisheries are subject to many stresses in addition to climate change (see Chapter 4). So far, events such as the 1998 mass coral bleaching in the Indian Ocean have not provided evidence of negative short-term bio-economic impacts for coastal reef fisheries (Spalding and Jarvis, 2002; Grandcourt and Cesar, 2003). In the longer term, there may be serious consequences for fisheries production that result from loss of coral communities and reduced structural complexity, which result in reduced fish species richness, local extinctions and loss of species within key functional groups of reef fish (Sano, 2004; Graham et al., 2006).
C2.3 Multiple stresses on coral reefs
C2.3.1 Non-climate-change threats to coral reefs of small islands (Chapter 16, Box 16.2)
A large number of non-climate-change stresses and disturbances, mainly driven by human activities, can impact coral reefs (Nyström et al., 2000; Hughes et al., 2003). It has been suggested that the ‘coral reef crisis’ is almost certainly the result of complex and synergistic interactions among global-scale climatic stresses and local-scale, human-imposed stresses (Buddemeier et al., 2004).
In a study by Bryant et al. (1998), four human-threat factors – coastal development, marine pollution, over-exploitation and destructive fishing, and sediment and nutrients from inland – provide a composite indicator of the potential risk to coral reefs associated with human activity for 800 reef sites. Their map (Figure C2.3) identifies low-risk (blue), medium-risk (yellow) and high-risk (red) sites, the first being common in the insular central Indian and Pacific Oceans, the last in maritime South-East Asia and the Caribbean archipelago. Details of reefs at risk in the two highest-risk areas have been documented by Burke et al. (2002) and Burke and Maidens (2004), who indicate that about 50% of the reefs in South-East Asia and 45% in the Caribbean are classed in the high- to very-high-risk category. There are, however, significant local and regional differences in the scale and type of threats to coral reefs in both continental and small-island situations.
Figure C2.3. The potential risk to coral reefs from human-threat factors. Low risk (blue), medium risk (yellow) and high risk (red). Source: Bryant et al. (1998)
Recognising that coral reefs are especially important for many Small Island states, Wilkinson (2004) notes that reefs on small islands are often subject to a range of non-climate impacts. Some common types of reef disturbance are listed below, with examples from several island regions and specific islands.
1. Impact of coastal developments and modification of shorelines:
- coastal development on fringing reefs, Langawi Island, Malaysia (Abdullah et al., 2002);
- coastal resort development and tourism impacts in Mauritius (Ramessur, 2002).
2. Mining and harvesting of corals and reef organisms:
- coral harvesting in Fiji for the aquarium trade (Vunisea, 2003).
3. Sedimentation and nutrient pollution from the land:
- sediment smothering reefs in Aria Bay, Palau (Golbuua et al., 2003) and southern islands of Singapore (Dikou and van Woesik, 2006);
- non-point source pollution, Tutuila Island, American Samoa (Houk et al., 2005);
- nutrient pollution and eutrophication, fringing reef, Réunion (Chazottes et al., 2002) and Cocos Lagoon, Guam (Kuffner and Paul, 2001).
4. Over-exploitation and damaging fishing practices:
- blast fishing in the islands of Indonesia (Fox and Caldwell, 2006);
- intensive fish-farming effluent in Philippines (Villanueva et al., 2006);
- subsistence exploitation of reef fish in Fiji (Dulvy et al., 2004);
- giant clam harvesting on reefs, Milne Bay, Papua New Guinea (Kinch, 2002).
5. Introduced and invasive species:
- non-indigenous species invasion of coral habitats in Guam (Paulay et al., 2002).
There is another category of ‘stress’ that may inadvertently result in damage to coral reefs – the human component of poor governance (Goldberg and Wilkinson, 2004). This can accompany political instability; one example being problems with contemporary coastal management in the Solomon Islands (Lane, 2006).