Kelp forests

 
Kelp is the largest and most structurally complex of all brown algae. It grows along rocky shores just below the low tide mark. Kelp is incredibly fast growing (with records of it growing 200m in a summer season) and forms multifaceted forests which teem with animals.

Giant kelp (Macrocystis pyrifera) forest, Santa Catalina Island, California. Photo courtesy of R. Cimberg

?If in any country a forest was destroyed, I do not believe nearly so many species would perish as would here, from the destruction of kelp? Charles Darwin, 1860.

The tropics are, for the majority, devoid of kelp. Vast forests occur along the Pacific coast of the US and off the Japanese coasts.
Kelp is harvested commercially for food and for other substances, like alginates, which are used as thickeners. It is big business world-wide and is cultivated in huge farms. Unfortunately the naturally occurring forests of kelp are facing the same pressures that many of the marine ecosystems around the planet are also pressurised by. Pollution and sewage from increased urbanisation has taken its toll on many kelp forests, as have pollution from heavy metals and oil. The removal of top predators, such as otters, that decrease sea urchin populations has lead to kelp being overgrazed and eliminated from some areas.