The Kelp Forests
Like the coniferous trees that make up that habitat on land, kelp thrives in cold conditions and grow in uniform abundance. The larger kelp forests are found in waters with temperatures no higher than 20°C (68°F), extending right to the edges of the Arctic and Antarctic Circles. Kelps are gigantic seaweeds and, like most of their smaller relatives, they require firm foundations on which to attach themselves. For this reason, they are only found around rocky coastlines where the seabed is solid or formed from large boulders.
Kelp Forests anchor themselves with structures known as holdfasts. These look like the root bundles of plants (kelp are algae, which are members of a related but distinct kingdom) but unlike them, kelps play no part in absorbing water or nutrients. Their sole purpose is to grow into cracks and crevices, filling them so that the kelp itself cannot be dragged away and washed ashore or swept out to sea.
Above the holdfast is the long, rope-like but flexible stem called stipe. This is immensely strong and has to be in order to withstand the buffeting of storm-driven waves. Growing from the stipe or extending from its end, depending on the species, are great strap-like fronds packed with photosynthesizing pigment. In some kelp, these can each stretch for dozens of feet. From holdfast to the tips of their most distant fronds, some kelp can measure nearly 200 feet (60m) long.
Kelp maintain their upright position in the water by means of large air-filled bladders. These ensure that the fronds receive as much light as possible, maximizing their ability to produce food. At low tide, the fronds are openly exposed to the air, but they never dry out. This is due to the presence within them of large quantities of algin, a substance they produce which is incredibly water retentive.
Various types of kelp occur in different parts of the world but all of them possess the same basic structure. In most of the areas where they are found they tend to form almost uniform submarine forests, dominated by a single species. In this way, they again closely mirror the forests of taiga that divide broad-leafed forests from tundra on land. Kelp adds a new and rare dimension to the underwater world, one of vertical structure. Creatures in kelp forests are not just restricted to the seabed or the open water. They also live on and among the fronds themselves. Sea snails munch away at the surface of kelp fronds, along with small isopods, the marine equivalent of leaf-eating insects.
The number of animals kelp forests support is surprisingly high. Different species prefer different zones. Senorita fish, for example, rarely venture far from the bottom, while topsmelt, as the name suggests, form small shoals in the canopy. Some creatures, such as the Pacific white-sided dolphin, regularly visit in search of food but do not live in the forests exclusively. Others are almost never found anywhere else.