Fishermen like Jose da Cruz have made their living for decades hunting for crabs among Brazil‘s vast coastal mangrove forests, dense thickets of twisted plants in deep black mud that grow where freshwater rivers meet the brackish Atlantic Ocean.

Da Cruz, who is known by the nickname Vampire because of his distinctive teeth, doesn’t use a rod and reel or a net. Instead, he parks his half a metre wide boat at the shore of the Caratingui River and wends his way on foot through the tangle of mangroves to dig out crabs with his hands from the dark muck.

He slowly begins to blend into his surroundings as he becomes increasingly caked in mud, sometimes lying flat to submerge his arm in search of crabs. He pulls out two of the spikey-legged creatures, larger than his hands.

The four or five dozen crabs he catches in a day will earn da Cruz about 200 reais ($50) a week, enough to get by, he said.

But this tenuous livelihood is facing a series of threats, including rapid alterations to the environment caused by climate change, and da Cruz’ average daily catch is half of what it was 10 years ago. In that time, the water line has advanced three metres inland from where it used to be, according to da Cruz.

Climate scientists lend credence to da Cruz’ interpretation of what he sees. Rising water levels, they say, are a sign of global warming, which also causes water temperatures to rise, killing off some marine life.

Globally, scientists have warned that water temperatures are increasing far faster than expected, which drives rising sea levels. Climate change and human development are putting nearly one million species, a large share of which live in marine environments, at risk of extinction, according to a report published this year.