Cohen Island is approximately 0.3 miles (0.5 km) across and is located at the northern entrance to Eldred Passage on the eastern shore of Kachemak Bay, about 8 miles (13 km) south of Homer, Alaska. The island was named by William Healey Dall of the U.S. Coast and Geodetic Survey after a local trader operating there in 1880. Eldred Passage, which is about 0.7 miles (1.1 km) wide, lies southeast of Yukon Island. This waterway was named for Sarah Eldred, the wife of Marcus Baker, a naturalist and explorer. Baker was hired by Dall to collect topographic and hydrographic data.

The rocky seabed around Cohen Island is home to bull kelp, an annual brown alga that forms extensive forests along the eastern Pacific coast, from central California to the eastern Aleutians. These forests thrive in waters generally less than 60 feet (18 m) deep. Kelp forests are highly productive ecosystems and serve as crucial shallow-water habitats, supporting a wide food web that includes algae, invertebrates, fish, seabirds, and marine mammals. In Kachemak Bay, the density of bull kelp forests varies yearly, but they consistently appear, especially along the southern shore, in narrow dense bands due to the steep nearshore bathymetry. The northern shore offers more shallow water habitat, resulting in larger but less dense kelp forests.

The abundance and distribution of kelp forests in Kachemak Bay and elsewhere depend on various factors, including water salinity, sedimentation, currents, and interactions with other plants and animals. Sea urchins, aggressive herbivores, can significantly limit algal growth and decimate kelp forests when present in large numbers. Sea otters, which feed on sea urchins, play a crucial role in controlling urchin populations. In regions where sea otters were hunted to near extinction, urchin populations surged, creating “urchin barrens,” areas devoid of kelp. Conversely, the recovery or reintroduction of sea otters in these regions has led to the resurgence of healthy kelp forests. Read more here and here. Explore more of Cohen Island and Kachemak Bay here: