Kelps also provide valuable spawning and nursery grounds for numerous species of fish and shellfish, which go on as adults to become the foundation for many commercial and recreational fisheries, such as the Atlantic cod, Gadus morhua. These smaller fish then attract larger predators like seals, sharks, and sea birds who hunt around the kelp canopies.
Threats and changes to kelp forests
Globally, kelp forests are increasingly threatened by a variety of human impacts, including climate change and fishing/hunting, harvesting, eutrophication.
Being a cold-water species, kelp forests are sensitive to elevated temperatures. As ocean temperatures increase as a result of greenhouse gas emissions, massive kelp forest die-offs are increasingly likely, with their return questionable. In some places, such as in Australia and Tasmania, we have already seen that kelps have not returned to areas they were once abundant.
Fishing through kelp forests using destructive methods like bottom trawling has also been implicated in dramatic declines of kelps, such as in the UK, while predator removal from fishing/hunting has likely changed ecosystem structure in many kelp forests. Few large animals graze on fresh kelps except for sea urchins; however, these animals can devastate a kelp forest, grazing until only denuded rocks, or barren grounds, are left. When urchins are removed, vegetation often rapidly returns, although the animals take longer. The reason for this overgrazing is still under debate but, in most cases, it is probably caused by predator removal leading to an increase in urchin populations. The most well-known example of this comes from the west coast of Canada and the United States, where sea otters were extensively hunted. As their population declined, urchin populations increased and grazed down the kelp forest. After the hunting of otters was stopped, the kelp forest returned.