Currently, 2.5 billion people (40% of the world’s population) live within 100 km of the coast,ref adding increased pressure to coastal ecosystems. Coastal development linked to human settlements, industry, aquaculture, or infrastructure can cause severe impacts on near shore ecosystems, particularly coral reefs. Coastal development impacts may be direct (e.g., land filling, dredging, coral and sand mining for construction) or indirect (e.g., increased runoff of sediment and pollutants).
Construction projects in coastal cities and communities may be built on land reclaimed from the sea. In many areas, wide shallow reef flats have been reclaimed and converted to airports, industrial, or urban lands. Dredging activities (e.g., deep-water channels, harbors, marinas) and dumping of waste materials in the coastal and marine environment can also damage and even destroy adjacent coral reefs.
Deforestation and clearing of vegetation can result in increases in sedimentation in coastal waters. For example, mangroves stabilize shorelines, trap sediments and filter pollutants and their removal results in coastal erosion and release of organic material and sediments that can wash onto and smother corals and change the water chemistry.
Land clearing and construction projects may change the natural drainage patterns, resulting in freshwater, nutrient, and sediment runoff onto adjacent reefs. Sedimentation can directly smother a reef or increase turbidity in the coastal waters, which reduces light available to corals and their symbiotic zooxanthellae. Corals depend on their zooxanthellae to generate food photosynthetically, therefore light deprivation can cause corals to starve. While some coral reefs thrive in turbid water, the reefs are typically less diverse and are more restricted in depth ranges than those in clear water.ref The combination of suspended, re-suspended, and deposited sediment can limit coral growth, feeding patterns, photosynthesis, recruitment, and survivorship.
Coral reefs are naturally adapted to low-nutrient waters, so the addition of nutrients can be particularly harmful for coral reef communities. Excess nutrients promote growth of macroalgae that can overgrow corals and prevent larval recruitment.
Sewage is one of the most widespread pollutants, and many countries with extensive coral reefs have little to no sewage treatment. For example, Southeast Asia, the Pacific, and the Caribbean discharge 80-90% of their wastewater untreated into the sea. ref Additionally, toxic chemicals from industries (e.g., mining), aquaculture, and agriculture, as well as households, parking lots, gardens, and golf courses wash into coastal ecosystems. Water treatment plants and power plants may also discharge chemicals into the coastal zone, significantly altering the water chemistry in these areas.
Impacts from Coastal Development
These include the following:
- Construction projects (piers, channels, airstrips, dikes, land reclamation, etc.) — can kill corals directly
- Degradation of coral reefs — can result in lost tourism revenue in countries that depend on reef-based tourism and also can reduce fish populations
- Coastal construction — can cause chronic sedimentation, sewage effluent, industrial discharge, and changes in water flow and runoff, which can adversely affect coral growth rates and metabolic activities as well as directly kill corals
- Removal of reefs — can result in beach erosion, land retreat, and sedimentation
- Sedimentation — can smother reefs or increase turbidity in coastal waters, thus reducing light needed for coral growth and survival
- Pollutants — can lead to increases in coral disease and mortality, cause changes in coral community structure, and impede coral growth, reproduction and larval settlement; for example, nutrient runoff can lead to algal blooms which can stifle coral growth
- Mining of coral for construction materials — can lead to long-term economic losses in terms of lost benefits for fisheries, coastal protection, tourism, and food security and biodiversity
As coastal populations increase and natural coastal protection is degraded or lost, sea-level rise and changes in storm patterns are likely to increase the effects of harmful coastal development activities. Local impacts of land-based sources of stress will occur in combination with global and regional stressors, such as climate change, land-use practices, and freshwater inputs, further threatening the survival of coral reef ecosystems. For example, increases in storm impacts linked to climate change could exacerbate run-off of sediments and other pollutants.
Reducing the effects of coastal development is critically important; it threatens nearly 25% of the world’s coral reefs, particularly in Southeast Asia, the Indian Ocean, and the Atlantic.ref The impacts of coastal development can be drastically reduced through effective planning and land use regulations. For example, planning and management approaches can include land-use zoning plans and regulations, protection of coastal habitats (such as mangroves), coastal setbacks that restrict development within a fixed distance from shoreline, watershed management, improved collection and treatment of wastewater and solid wastes, and management of tourism within sustainable levels.
Reefs at Risk Revisited (pdf, 6.4M)