SHINNECOCK NATION, Southampton, N.Y. — A maritime people who once spanned a large swath of the eastern Long Island shore, the Shinnecock Indians have been hemmed into a 1.5-square-mile patch of land on the edge of a brackish bay. Now, because of climate change, they’re battling to hold on to what they have left.

Rising seas are threatening to eat away at the Shinnecock lands. But the tribe is using everything at its disposal to calm the waves and restore a long, slim beach at the edge of Shinnecock Bay: dredged sand, sea grasses, beach grasses, boulders, oyster shells.

It’s a forever battle. Climate change is swelling and heating the world’s oceans at an accelerating pace. Inevitably, the Shinnecock will have to bring more sand to replenish what the rising tide keeps washing away. More grass will have to be planted. This spring, Shavonne Smith, director of the tribe’s environmental department, wants to expand the oyster reef designed to dissipate the energy of the waves.

“We have an inherent responsibility to protect the homeland,” Ms. Smith said on a recent Monday morning walk along the shore. “It’s not the type of thing where you can work against nature. You work with it.”