This type of kelp has not been observed in this location before, and is spread all over the north end of Zachary Bay.
Mandy Lindberg, Fisheries Research Biologist with the National Oceanic and Atmospheric Association (NOAA), writes:
That is the Giant Kelp, Macrocystis pyrifera. Its northernmost distribution is normally Prince William Sound with larger beds west in the Kodiak Archipelago. It could have been inadvertently introduced by visiting vessels or oceanographic currents. It appears the trend of warmer waters in the Gulf of Alaska are allowing it to persist. This species is not a nuisance species but rather a valuable habitat and commercial species forming diverse canopies of kelp forests. It will be good to keep tabs on this bed to see if it remains in the future.
Comments from LEO Editors:
Giant kelp (Macrocystis pyrifera) can be found from Alaska down to Baja California, and is a perennial kelp species that can live up to seven years. Kelp forests provide a source of food, and prey habitat, for a variety fish, marine invertebrates, and marine mammals. Marine mammals and sea birds may also seek shelter in kelp forests during strong ocean storms, and fish species such as herring and Atka mackerel use kelp to spawn. Source: Glacier Bay National Park and NOAA National Marine Sanctuary "Kelp Forest" informational pages. Sarah Ingram and Erica Lujan
See also: Jordan A. Hollarsmith, Alejandro H. Buschmann, Carolina Camus, Edwin D. Grosholz. Varying reproductive success under ocean warming and acidification across giant kelp (Macrocystis pyrifera) populations. Journal of Experimental Marine Biology and Ecology, 2020; 522: 151247 DOI: 10.1016/j.jembe.2019.151247