Oceans

Oceans comprise 76% of the tropics by area. Tropical oceans are generally shallower and warmer than in other regions and tend to be lower in nutrients hence support lower densities of marine organisms. They do, however, support the most biologically diverse marine ecosystems on the planet.

Oceans, and in particular coastal marine waters, are fundamental to the health and wellbeing of many communities in the tropics with a large proportion of the human population dependent on marine resources for sustenance and livelihoods. Valuable income is also generated from coral reef and beach associated tourism. Oceans also provide important global protective, regulatory and supporting ecosystem services with their role as a carbon sink, in climate regulation and in nutrient cycling.

Fish are the primary source of animal protein for many coastal communities worldwide. Communities that rely on small-scale fisheries are largely located in the tropics and about half the wild marine fish catch is taken by these small-scale operations. Commercial operations are also increasingly influential in the tropics. Sustainable management of marine catch is essential to maintain the ecological integrity of oceans as well as providing a sustainable resource for coastal communities into the future.

Globally, wild marine catch quadrupled between the 1950s to when it peaked in the mid-1990s. Since then catches outside of the tropics have declined or stabilised despite increasing fishing effort. By comparison, exploitation of wild marine resources in the tropics has grown rapidly over the past 60 years. Although lower in overall fish biomass, the tropics’ share of the overall global wild marine fish catch is increasing. Greater demand for seafood from a growing and increasingly affluent population, combined with better technology and greater fishing effort by international vessels in tropical waters, means pressures on marine fish stocks are likely to increase further.

Aquaculture is the cultivation of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants under controlled conditions. Increased aquaculture production is associated with a transition to more sustainable fishing practices. Assuming continued population growth and constant per capita demand for seafood, responsible aquaculture represents the best hope of both meeting demand and halting the decline of wild stocks.

In 2010, the tropics produced 36% of reported global aquaculture production, up from 26% in 1950. The rapid growth in tropical aquaculture, particularly of monocultures, has had negative environmental effects, including impacts on water quality and the introduction of invasive species. However, significant improvements are being made in productivity and environmental practices, including placing a greater emphasis on diversifying types of fisheries used.

The vast majority of coral reef systems are located in the tropics. They are the most biologically diverse marine ecosystems and provide a range of goods and services to tropical nations. For many nations, coral reefs are important for fisheries, provide protection to coasts and are an important source of income through tourism.

Coral reefs in all tropical regions are suffering from increased local and global threats. Impacts on reefs increased markedly between 1998 and 2010 with about 80% of all tropical reefs now considered to be at medium or high risk of damage.

The main local threats to reefs include coastal development, overfishing, destructive fishing practices, pollution and sedimentation. Increased water temperatures and ocean acidification are the greatest global threats. Loss of coral reef systems is having wider ecosystem and human well-being ramifications because of declining fish populations and erosion of protective services offered to coastal communities.

Mangroves are important nurseries and habitats for marine life. They help filter pollutants from land-based run-off and help protect nearby coral reefs, seagrass beds and coastal infrastructure. The tropics host nearly 95% of the world’s mangroves by area and 99% of all mangrove species.

Mangrove forests have decreased in area since 1980 in all tropical regions. The greatest threats to mangroves include illegal forestry, coastal development, impacts from aquaculture and pollution. Loss of mangroves increases the risk of adverse impacts of extreme weather events on coastal communities and contributes directly to losses of fisheries resources. Some tropical nations have recognised the value of mangrove ecosystems and are improving legislative protection as well as initiating reforestation efforts to improve coastal mangrove systems.