Crabs, worms, some algae, and small crustaceans. Black Prickleback live close to shore in rocky areas with algae cover. They are primarily found in the lower intertidal and shallow subtidal zones.
Small ones are common in the tidepools.
They don't get any longer than twelve inches. Spawning takes place from February to April off the central California coast and in late April to May off British Columbia. Black Prickleback make nests underneath boulders in the lower intertidal areas. As a female lays an egg, a male fertilizes it, and the pair shapes each fertilized egg into a sphere. Females lay 738 to 4,070 eggs.