Hexagrammos decagrammus, commonly known as the kelp greenling, is a marine fish found along the rocky coastlines of the northern Pacific Ocean. It exhibits sexual dimorphism, with males displaying a striking pattern of blue spots on their heads. The species thrives in kelp forests, contributing to the ecosystem by preying on small invertebrates and serving as prey for larger predators.

Hexagrammos decagrammus, commonly known as the kelp greenling, is native to the northeastern Pacific Ocean. Its geographical distribution ranges from the Aleutian Islands in Alaska, down the coasts of British Columbia, Washington, Oregon, and California, and as far south as La Jolla, California.

The kelp greenling is typically found in nearshore, rocky coastal environments where kelp forests are abundant. These environments offer a complex structure of rocky reefs and kelp beds, providing both shelter and feeding opportunities. The species thrives in cold, temperate marine waters, where water temperatures generally range from 5°C to 15°C (41°F to 59°F).

Hexagrammos decagrammus occupies a niche as a benthic predator within kelp forest ecosystems. It primarily feeds on a variety of marine invertebrates, including crustaceans, mollusks, and small fish. The kelp greenling plays a role in controlling the population of these invertebrates, contributing to the ecological balance within its habitat.