The scale of human impacts on reefs has grown exponentially and pollution from agriculture and land development has been one of the main causes of the significant decreases in abundance of coral reef species (Hughest et al., 2003). The runoff of soils, fertilisers and pesticides from agriculture have significantly affected coral reefs (De’ath et al., 2012).
On some reefs, overfishing and added nutrients from activities on land has caused an ecological shift from corals dominating the ecosystem to seaweed species dominating. Figure 12 shows the runoff directly from land into the open ocean, only a few hundred yards from a coral reef.
Coral reefs live in very nutrient poor waters and are very sensitive to change, meaning an increase in nutrients due to runoff could be extremely damaging (Pastorok and Bilyard, 1985).
Increased runoff due to urbanization and the release of toxic substances can decrease the salinity in the water and lead to coral bleaching (Moberg et al., 1997). Bleaching is the loss of the symbiotic zooxanthellae on the corals (Brown, 1987). Due to the disturbed symbiosis and bleaching of coral reefs, the nutrition and growth will be affected (Richmond, 1993).
Therefore, the ability to deliver services and goods to humans will be reduced.