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Global Biodiversity Outlook 3

Coastal and marine ecosystems

Current path:

Demand for seafood continues to grow as population increases and more people have sufficient income to include it in their diet. Wild fish stocks continue to come under pressure, and aquaculture expands. Progressively fishing down the marine food web comes at the expense of marine biodiversity (continuing decline in marine trophic index in many marine areas). Climate change causes fish populations to redistribute towards the poles, and tropical oceans become comparatively less diverse. Sea level rise threatens many coastal ecosystems. Ocean acidification weakens the ability of shellfish, corals and marine phytoplankton to form their skeletons, threatening to undermine marine food webs as well as reef structure. Increasing nutrient loads and pollution increase the incidence of coastal dead zones, and increased globalization creates more damage from alien invasive species transported in ship ballast water.

Impacts for people:

The decline of fish stocks and their redistribution towards the poles has major implications for food security and nutrition in poor tropical regions, as communities often rely on fish protein to supplement their diet. The impact of sea level rise, by reducing the area of coastal ecosystems, will increase hazards to human settlements, and the degradation of coastal ecosystems and coral reefs will have very negative impacts on the tourism industry.

Alternative paths:

More rational management of ocean fisheries can take a range of pathways, including stricter enforcement of existing rules to prevent illegal, unreported and unregulated fishing. Scenarios suggest that the decline of marine biodiversity could be stopped if fisheries management focuses on rebuilding ecosystems rather than maximizing catch in the short-run. Fishery models suggest that modest catch reductions could yield substantial improvements in ecosystem condition while also improving the profitability and sustainability of fisheries. The development of low-impact aquaculture, dealing with the sustainability issues that have troubled some parts of the industry, would also help to meet the rising demand for fish without adding pressure on wild stocks.

The reduction of other forms of stress on coral systems may make them less vulnerable to the impacts of acidification and warmer waters. For example, reducing coastal pollution will remove an added stimulus to the growth of algae, and reducing overexploitation of herbivorous fish will keep the coral/algae symbiosis in balance, increasing the resilience of the system.

Planning policies that allow marshes, mangroves and other coastal ecosystems to migrate inland will make them more resilient to the impact of sea level rise, and thus help to protect the vital services they provide. Protection of inland processes including the transport of sediments to estuaries would also prevent sea level rise from being compounded by sinking deltas or estuaries.

  • United Nations
  • United Nations Environment Programme