AquaMarine Life

Kelp forests occur in cold, nutrient-rich water and are among the most beautiful and biologically productive habitats that you can find in the marine environment. They are found throughout the world in shallow open coastal waters, and the larger forests are restricted to temperatures less than 20ºC, extending to both the Arctic and Antarctic Circles.

A dependence upon light for photosynthesis restricts them to clear shallow water and they are rarely much deeper than 15-40m. The kelps have in common a capacity for some of the most remarkable growth rates in the plant kingdom. In southern California, the Macrocystis can grow 30 cm per day.

Kelp forests are very productive and support areas of high plant biomass. This is an infrared-sensitive air photograph, taken with a view towards the shoreline; chlorophyll is visualized as a “false color” red. The intense red indicates rocky benches covered by the seaweed Hedophyllum, whereas the wispy red represents subtidal kelps.

Kelp forests on the east coast of North America have fewer species but often are quite lush, and support rich communities of benthic invertebrates. They range southward to Cape Cod and occur only sporadically southward to the eastern tip of Long Island, New York. Urchins are important grazers and may reach densities sufficient to eliminate the kelp forest.

This Alaskan kelp forest site is dominated by Laminaria groenlandica (foreground). If urchins are relatively sparse and disturbance infrequent, this species tends to take over. It is a perennial, and shades out other species, including the annual Nereocystis luetkeana, which can grow to the surface, if it can get a start from the bottom. When Laminaria is sparse this is possible, but when it is very dense, thalli shade out newly established sporelings of Nereocystis.

Nereocystis luetkeana often dominates northeastern Pacific kelp forests. It has a long stipe that is attached often to a small rock and is kept aloft by a gas-filled float. The fronds extend from the float. This makes for a very unstable arrangement and strong storms often uproot the plant. This kelp is an annual, so more low-lying perennial seaweeds can take over simply by outshading Nereocystis when the sporelings begin to grow from the bottom.

In the Pacific northwest, subtidal kelps are dominated by Agarum fimbriatum, a leafy laminaria-like plant. Their dominance may relate to their high concentrations of secondary compounds that defend them from urchin grazing. From the surface, however, you will probably more likely notice the enormous fronds and floats of Nereocystis luetkeana.
Kelp forests are rich in animal species.

Large number of suspension feeders found on kelp forest bottoms can be associated with kelp detritus, by means of similarities in abundances of a number of stable isotopes. The reason for benthic abundance may also relate to the concentrated settlement of planktonic larvae beneath kelps, where water flow is relatively more sluggish than in more exposed hard bottoms. Recent research shows that suspension feeders such as mussels and serpulid polychaetes grow well when fed particles of kelp.