Marine Heat Waves Are Putting Caribbean Fisheries In Hot Water

Small-scale fisheries are a critical component of the social and economic and fabric of coastal communities in the Caribbean and are key to the region’s food security, with annual fish consumption ranging between 10 and 35 kg/capita per year (FAO, 2014). But marine heat waves (MHW) or extended periods of anomalously warm ocean temperatures¹ can have major impacts on marine biodiversity and ecosystems, and are a significant threat to the regional fisheries sector. A 2019 study in journal, Nature Climate Change, reports that coral reefs in the Caribbean have been among the hardest hit by heat waves, and the Food and Agriculture Organisation has found that the Caribbean fisheries sector is most vulnerable to climate change in the world. (Monnereau, 2017)

According to a September article in journal, Science, as global warming makes oceans hotter, marine heat waves (MHW) have become at least 20 times more likely. “The duration, intensity, and cumulative intensity of most documented, large, and impactful MHWs have increased more than 20-fold as a result of anthropogenic climate change,” say the authors.

Marine heat waves and other environmental extremes, have been shown to have stronger impacts than gradual changes over longer time periods. The impact of these extreme conditions can be devastating to ecosystems, affecting species mortalities, causing changes in the structure and types of species that exist within the ecosystem and lowering the productivity of marine life.

Hurricanes

Warm ocean waters are known to strengthen tropical storms and hurricanes, resulting in an increase in the frequency of category 4 and 5 hurricanes in recent years. Marine heat waves exacerbate these effects.

Hurricanes have been known to affect ocean habitats up to 300 feet below the surface and hurricane-induced tides can create immense damage to the structure of coral habitats on which reef fish rely for their existence. Waves can also bring up colder waters, with less dissolved oxygen from the deep, causing marine animals to suffocate and die.

Major hurricanes also impact fisheries through damage to fisheries-related resources. Hurricane Maria in Dominica, for example, destroyed more than 40 percent of fishing vessels and gear, as well as ice machines, locker rooms and other infrastructure, disrupting value chains for an extended period. (Monnereau)

Coral reef bleaching

Persistently high sea surface temperatures contribute to coral bleaching by causing corals to expel vital algae that can lead to death. Marine heat waves have been found to kill corals quicker than typical bleaching events, due to a build up of bacteria that causes them to breakdown more rapidly.

There are more than 800 species of coral throughout the world’s oceans with about 60 of these species found in the Caribbean. Because corals are unable to relocate to cooler waters, they do not fare as well as mobile species, such as fish, making them more vulnerable to death. As reefs provide both habitats and resources for many interdependent species, the impacts cascade across the ecosystem.

Depletion of fish stocks

While reefs only make up about one per cent of the ocean floor, they are home to 25 per cent of marine life and are associated with approximately 500 to 700 Caribbean species of fish.

Marine species respond to heat waves by moving into unoccupied habitats, either deeper or further from shore. As they change their location, fish catches are altered. Further, given the degradation of their habitat, the health and mortality of reef fish can be negatively impacted if they do not relocate.

Studies have shown that temperature-induced mass coral bleaching has resulted in the decline of reef fish in Cuba, and reductions in the biomass of herbivorous Caribbean reef fish due to increases in sea surface temperatures. The decline in sardine populations has been linked to climate-induced reduction in phytoplankton productivity in the southern Caribbean and the size and availability of flying fish and mahi mahi (known as dolphin fish in the region) has been impacted by climate-induced sargassum influxes. (Monnereau, 2017)

Iris Monnereau and Hazel Oxenford predict that “changes in availability of high-value species (e.g. spiny lobster, conch, shrimp and snapper) will have particular impact on the harvest sector (both small-scale and semi-industrial) as fishers productivity and catch per unit of effort will go down.” (2017)

The implications

A relatively new area of research, marine heat waves have far reaching effects on the environment, livelihoods and food security in the Caribbean region. Monnereau and Oxenford predict that “reef-associated fisheries, already severely degraded, and on which the region is heavily reliant, will be hardest hit by current and near-future climate change impacts” such as marine heat waves.

These predictions are a cause for concern, given the strategic significance of the sector.

Caribbean fisheries provide an essential source of protein to Caribbean people and contribute to regional livelihoods, particularly in coastal communities, with at least 64,000 persons directly employed in small-scale fisheries and aquaculture and a further 180,000 people involved in related activities. From the perspective of trade, annual exports of fish and seafood from the fifteen nation CARICOM region have been estimated at $400 million (2016).

A decline in fisheries would have consequences for employment, food security, foreign exchange, culture and other industries, including tourism. Reducing the climate vulnerability of the sector is therefor of utmost strategic value.

The Food and Agriculture Organisation’s CC4FISH ‘Climate Change Adaptation of the Eastern Caribbean Fisheries Sector’ project supports adaptation measures across the fish chain in Antigua and Barbuda, Dominica, Grenada, St. Kitts and Nevis, Saint Lucia, St. Vincent and the Grenadines, and Trinidad and Tobago to improve climate resilience.

SASAP, Saint Lucia’s Sectoral Adaptation Strategy and Action Plan for the fisheries sector “seeks to strengthen the sustainability of Saint Lucia’s fisheries and fishery-dependent businesses and the security of fisheries-dependent livelihoods under a changing climate” and is currently in the proposal stages of an implementation project organised by the Food and Agriculture Organisation and Global Affairs Canada.

With more than 90 per cent of planetary warming taking place in the ocean and given the sector’s many social, economic and environmental dependencies, the need to enhance the climate resilience of Caribbean fisheries is paramount.