Nutrient loading occurs when an influx of nutrients, such as dissolved inorganic nitrogen (N) and phosphorus (P), enter a coral reef system (Reopanichkul et al., 2009; McCook 1999). Depending on the locality, there can be several different sources of nutrient flux with the most common ones being untreated sewage discharge (Reopanichkul et al., 2009) and fertilizer runoff from agriculture (WRI, 2011). In areas with tourism development, unsustainable landscaping practices can also add to fertilizer runoff (WRI, 2011).
Local stress from sedimentation refers to the amount of sediments entering coral reef systems and the associated amount of suspended particles at any given time (Rogers, 1990). Increased sedimentation results from coastal development and watershed land-use change. Specifically, near shore dredging activities for beach nourishment, port construction or urban land reclamation can increase the amount of suspended particles in the water and real estate development along the shore destroys natural sediment traps like mangroves and wetlands (Rogers, 1990). Further inland and upland, deforestation greatly increases erosion and sediment influx to the watershed (WRI, 2011).
Chronic overfishing was not immediately recognized as a threat by coral reef researchers (Hughes, 1994). However, growing coastal populations and their associated consumption of seafood has driven fisheries down the food chain from larger predatory species like snappers, triggerfish, and groupers, to smaller herbivorous reef grazers like parrotfish and sturgeonfish (Hughes, 1994).
Direct physical contact as a result of various human activities can abruptly and severely damage coral reefs. This includes dislodging of coral, fracturing of the reef structure, and pulverization of the calcium carbonate skeleton of corals (Jaap, 2000). Physical damage comes from the hull and anchor impact of vessels, and certain types of fishing such as trawling and dynamite fishing (Jaap, 2000).d susceptibility to other stressors