Modern Tropical coral reefs are under threat, mainly as a result of human activity. All of the destructive factors work together to reduce the resilience of the reef. Resilience is the ability of an ecosystem to absorb recurrent disturbances and retain the same function, structure and feedbacks (Walker et al., 2004). Resilience is lost through complex interactions of a combination of threats. Once a reef has lost it resilience it will exhibit a phase shift from the coral dominated system, often towards an algal dominated reef (Knowlton, 2001). The phase shift generally occurs relatively quickly in healthy looking reef (Ostrander et al., 2000), because the reef’s resilience is ‘eroded’ away by background threats such as increased nutrients. The actual phase shift is triggered by a new or short term destructive force such as hurricanes, crown of thorns outbreaks, bleaching etc. (McManus and Polsenberg, 2004) (Figure 8).

The reduction in grazers because of over-fishing, and increased nutrient concentrations are dominant factors leading towards phase shifts, hence it is important to manage fish stocks and urban/agricultural runoff (McCook, 1999; Hughes et al., 2007). Marine protected areas and no take zones are important for the regulation of fish pollutions and hence allowing areas of a reef to recover after a disturbance (Hughes et al., 2003).

Figure 8- The sudden nature of a phase shift. Adapted from Hughes (2008)

On the other hand small scale disturbances can be beneficial for the reef (Sebens, 1994) because they open up patches for the development of fast colonising species so the low diversity climax community does not occur (Connell, 1978), but once the disturbance becomes large and frequent the biodiversity becomes very low and a phase shift is more likely to occur.

To conclude our reefs are under serious threat as a result, either direct or indirectly, of our actions. If we don’t act now global coral reefs could be lost. In order to save the coral reefs action needs to be taken to reduce climate change and manage the reefs on a local scale such as diverting sewage elsewhere, managing fish stocks, and reducing the damage we create on reefs.

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