Fishermen in Haiti and some African countries could lose their livelihoods as ocean acidification causes a decline in mollusc populations, a study has found.
Human industrial activities release carbon dioxide, which dissolves in sea water, increasing its acidity. This higher acidity damages the mollusc stocks on which many fishermen in Gambia, Haiti, Madagascar, Mozambique and Senegal rely.
Fishermen in Bissau, Guinea-Bissau. Overfishing has depleted once-bountiful African waters.
"Laboratory studies show that animals that make hard shells and skeletons out of calcium carbonate minerals have a more difficult time doing so when ocean acidification lowers the carbonate concentration in sea water," said Sarah Cooley of Woods Hole Oceanographic Institution, United States, the study's lead author.
There is a clear link between increasing ocean acidification and decreasing carbonate production for shells in molluscs such as clams, scallops and conches.
"It takes more energy for these animals to create and maintain calcium carbonate structures, so they have less energy for other important life functions like reproduction, growth and metamorphosis," she added.
The study, published in Fish and Fisheries last month (7 July), says that mollusc fisheries will decline most in poor countries that are already struggling with protein deficiencies.
It assessed countries' vulnerability by looking at their reliance on mollusc fisheries, their capacity for aquaculture and their projected population growth. Aquaculture may help control factors such as acidity levels, helping nations to adapt.
It found that, 10-50 years from now, many developing countries will face smaller mollusc harvests, with the five countries mentioned above to be hit the hardest. This leaves a narrow window of opportunity for policymakers to devise strategies that allow fishermen to continue benefiting from mollusc fisheries.
Molluscs are a high-quality source of protein and exporting them generates income for some developing countries, Cooley said. In Madagascar, for instance, fishing provides seven per cent of the gross domestic product (GDP) and generates nearly half-a-million jobs, according to 2005 data.
But a combination of nutritional, economic and oceanographic factors, such as protein loss, erosion of income, climate change and ocean acidification, makes these nations particularly vulnerable, Cooley said.
In Madagascar, the effects of ocean acidification and climate change are already being experienced, according to Jean Maharavo, acting director of science at the Ministry of Higher Education and Scientific Research.
"My recent work shows a close correlation between decline in shellfish harvests and environmental decline in the southwestern parts of the island," he told SciDev.Net.
Urgent measures are needed to protect submarine areas and to ensure the sustainability of mollusc stocks, he said, adding that alternatives to mollusc fishing must be found.
Cooley said that, for adaptation to be successful, vulnerable nations must also include pollution, overfishing and climate change in their plans.