Zoom sur les pêches : changement climatique et pêche côtière dans le Pacifique

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How does the ocean temperature rise in the Pacific region affect food security of Pacific islanders? 

There is no simple, or single, answer to this question as outcomes and effects will be variable across such a vast region as the Pacific islands. Climate change effects will also be influenced by local factors such as pollution, dredging/reclamation, overfishing and over population. Therefore, while relatively pristine or healthy systems will still suffer from climate change effects, they might be expected to display more resilience than areas where anthropogenic (human-caused) impacts are greater and more chronic.

From a coastal habitat perspective, the most overt impact of rising ocean temperatures on Pacific Island Countries and Territories (PICTs) has been the increase in the spatial and temporal extent of “mass coral bleaching” events. Global and regional scale coral bleaching has become more common with extensive mortality of hard and soft corals happening due to bleaching events over multiple years. The flow-on effects of losing such large amounts of core coral habitat are being more frequently documented with evidence that fish and invertebrate communities, which rely on coral reef ecosystems for their survival, are being fundamentally changed. 

As well as being a key source of food and shelter for communities, coral reefs also buffer the erosion effects of waves and swells on island shorelines. Degraded coral reefs not only support less fish and invertebrates, but they also become less effective at moderating shoreline erosion around island communities. This situation is escalating because rising ocean temperatures are also causing sea levels to rise, which works in tandem with eroding reef systems to cause more frequent inundation of coastal land and higher levels of erosion. Drowning of land has direct effects on agricultural output, another mainstay of food security in the PICT’s.

Warming ocean temperatures are also a key driver of weather and climate across the region with storms, cyclones, swells and rain all heavily influenced by temperature. More powerful cyclones will speed up the impacts of degrading coral reefs and rising sea levels, as well as increasing damage to critical infrastructure and lives. Communities that regularly deal with extensive damage will not have the energy or resources to spend on ensuring their food security. On atolls, the rising sea levels, combined with increasing frequency and intensity of storms, are already causing saltwater intrusion into the freshwater lenses and taro patches.

Water temperature is a key component of modulating ocean acidity, with increasing temperature increasing the acidity of sea water. The effects of ocean acidification are many and varied with the chemistry behind ocean acidification considered a driver of multiple effects. Organisms that produce a calcium-based skeleton, such as corals, clams, oysters and lobsters, are vulnerable to a more acidic environment due to a reduced uptake of calcium carbonate, resulting in thinner skeletons that are more prone to damage. Water chemistry is critical to so much of the life cycle of marine organisms with documented effects on, for example, fertilization rates, larval development, and the ability of fishes to avoid predation. Changes to the chemistry of seawater due to climate change are already having a significant effect on marine productivity and the global carbon cycle upon which life depends.

On the grandest scale, increasing water temperatures are affecting the global movement of the cold oceanic deep water which underpin the current systems of the world. These currents drive the current climate patterns and if significant changes occur to these systems, it is unlikely they will be reversed, even if global warming processes are substantially reduced.    

Impacts on Pacific people reliant on fishing for their livelihoods and food? 

Substantial loss of coral reef habitats and associated ecosystems (seagrass meadows for example have suffered badly from heat waves and also cyclone-related turbidity) will reduce the habitat needed for many species of fish and invertebrates to recruit to, shelter in and feed on. This will lead to substantial changes in the abundance and distribution of many species that are part of food fish assemblages across the Pacific. 

Continued loss of coral reef habitats will inevitably lead to a permanent shift in the type of fish and invertebrate communities that inhabit ‘coral reef’ ecosystems, with a likely rise in herbivorous animals taking advantage of an increased dominance by algae, which will replace corals.

Many invertebrates, which are a large part of fishers’ catches, are also likely to become more vulnerable through a combination of heat stress, reduced calcification of their skeletal structures and greater exposure to storms and cyclones.

A potentially more significant issue are the effects of climate change on the early and relatively less well studied parts of the life cycle of fish and invertebrates. Changes to the reproductive capacity of fishes and invertebrates, the access to food when they are part of the plankton and their ability to grow and recruit successfully to their adult habitats are all possible under changing climate conditions. Very small differences at the beginning of the life-cycle can have very profound changes on adult populations and their ability to persist.

Perhaps the largest affect will be on social and socio-economic systems within the Pacific which are so intrinsically bound to the sea. Large changes in the availability of marine protein could have major flow-on effects which could de-stabilize work-life systems that have been in place for millennia.

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Andrew Halford

Chargé de recherche halieutique principal (pêche côtière), Division pêche, aquaculture et écosystèmes marins, CPS