Sunlight streams through a canopy of leafy, stemmed structures that tower above the ground from tens to hundreds of feet. Their leafy blades wave slowly while small, spiny animals crawl even more slowly around their bases. A furry animal darts through the green after one of the spiny creatures, and a teeming school of fish passes overhead. Wait . . . fish in a forest?
The picture I was painting above was of a forest of the sea specifically known as a kelp forest. These kelp forests are aptly named, since like any forest on land, they support their own ecosystems: they grow in dense thickets and are a source of food as well as potential shelter from predators and severe weather. Examples of organisms they support include whales, seals and sea lions, sea otters, a variety of seabird and shorebird species, sea urchins, starfish, and a litany of fish species.
Above: Kelp forest ranges. Image credit Maximilian Dörrbecker (Chumwa), CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0 via Wikimedia Commons
Kelp forests typically occur in cold and nutrient-rich waters, which are usually also shallow and give the kelps good sunlight. Kelps have been known to grow incredibly fast and tall in good conditions. Some, like the giant kelp species of the genus Macrosystis, can grow up to two feet a day and heights height of over 200 feet. Kelp species' knack for fast growth gives them an advantage in rough environments such as storms, after which they can quickly rebound.
Kelps are complex! Let's take a closer look at what they are below.
Kelps are not true plants. Kelp actually refers to certain macroalgae--that is, single-celled algae that grow together in large plant-like structures. All kelps are made of a kind of algae classified as "brown algae," named for the pigments they use for photosynthesis (brown algae don't always look brown, however)! Like plants, kelps get energy from sunlight, have leaf-like "blades", stem-like "stipes", and root-like "holdfasts" to anchor them to the ocean floor. However, kelps don't always primarily depend on their root-like holdfasts for nutrients, have a complex vascular system (veins) to transport water and food, or depend on their leaf-like blades to get energy from sunlight--each one of the algal cells that compose a kelp body often share these tasks! Some have air-filled gas bladders on their blades to hold themselves upright, too.
Left: Photo credit Clark Anderson, CC BY-SA 2.5 via Wikimedia Commons https://creativecommons.org/licenses/by-sa/2.5
Right: Photo credit Gustavo Gerdel, CC BY-SA 4.0 via Wikimedia Commons https://creativecommons.org/licenses/by-sa/4.0
Global warming has been a problem for kelp in recent decades; as ocean temperatures rise, the waters of their usual home ranges become nutrient-poor with the changes in temperature and the kelps wither for lack of food. Human impacts also play a big role in their recent troubles; one large factor we impose is overharvesting key species associated with kelp forests, which shifts the local food web's balance against the very presence of the kelps themselves. The key species we've upset are sea otters and lobsters; they feast on sea urchins, which, if left unchecked, turn kelp forests into wasted barrens.
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