Food security problems caused by climate change and ocean acidification will hit small island and coastal nations hardest, environmental group Oceana said on Monday.

The Comoros islands in the Indian Ocean headed the non-profit group’s rankings of nations most vulnerable to the combined effects of higher carbon dioxide emissions and ocean temperatures, and the increasing acidity of the world’s water.

Nations that depend heavily on seafood as a source of protein may face increased food insecurity, with shellfish like oysters, clams and mussels particularly vulnerable, it said.

Togo, the Cook Islands, Kirbati, and Eritrea rounded out the report’s top five.

“Most of the nations that will suffer have done very little to cause climate change,” the study’s author, marine scientist Matthew Huelsenbeck, said, noting those hardest hit rely on small-scale fishermen who are not equipped to chase retreating fish into colder, deeper, and more distant waters.

The report coincided with the third ‘Symposium on the Ocean in a High CO2 World’ in the Californian coastal town of Monterey, which is addressing increased ocean acidification.

The Intergovernmental Panel on Climate Change is due to report in 2014 on ocean acidification, which the symposium estimated had advanced by 30 percent since the start of the industrial revolution.

Climate change was projected to worsen over the next half-decade, and fishing industries in the United States and developed nations would suffer too, the Oceana report showed.