Climate: large-bodied fish not punching their weight


When it comes to resisting environmental hazards, size does not equal strength. On the contrary: large-bodied fish suffer the most from increases in temperature and human activity, as shown by an international study conducted in the Indo-Pacific. For instance, the populations of some parrotfish or large groupers could drop more than two-thirds below critical climate impact and anthropogenic thresholds.

The biodiversity of fish is declining throughout the world. The most vulnerable species are the subject of special attention from scientists.

Large but not strong

Faced with climate change and the anthropogenic pressure applied on tropical coastlines, large species are the most vulnerable, such as certain types of parrotfish and groupers. Furthermore, this is the first time that the dual impact of mankind and the climate on the biodiversity of coral ecosystems has been demonstrated thanks to local observation data.

These results are the fruit of a study conducted on a vast ensemble of coral reefs in the Pacific and the Indian Ocean, published in the journal Nature Communications. This involves a large team of French scientists from IRD, the Universities of Montpellier and New Caledonia and EPHE. The researchers have united, in one of the world’s largest reef fish databases, over 10,000 scuba diving observation centres. This corresponds to several million fish from hundreds of different species.

A decrease in the population by two-thirds

The researchers, using models, have estimated the factors which play a role in the abundance of these reef fish. Four factors highly significant: the size of the species, the size of their area of distribution, variations in the water temperature and the density of the human populations in the surrounding area. Of the 240 species analysed by the scientists, the abundance rate of fifteen of them, among the most geographically restricted and measuring over 50 cm when they reach adulthood, falls by more than 67% when climate change and the development of human activities exceed certain critical thresholds.

Food safety in jeopardy

This observation is all the more alarming as large-bodied fish directly meet the food and economic requirements of many emerging countries in addition to the role they play in ensuring the good health of the reefs. In some regions, these species are heavily exploited e.g. the blue parrotfish and large groupers and their numbers are now low particularly in the areas with the highest level of diversity such as in the “Coral Triangle” area. This area features the planet’s greatest marine biodiversity between Malaysia, Indonesia, the Philippines and the Solomon Islands representing 1% of the Earth’s surface.

These results highlight the need to pay special attention to these most vulnerable species. Building this knowledge into conservation strategies could help reduce the human impact on these threatened populations.

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