Kelp forest

Kelp forests are incredibly productive and dynamic underwater ecosystems.

They consist of high densities of brown macroalgae known as kelp. These forests cover large parts of the world's temperate and polar coastlines. While they only cover 0.1% of the Earth's total surface, they account for 0.9% of global primary productivity. This high productivity makes them essential to marine life. They provide complex habitats for many different organisms.

An individual kelp organism is called a thallus. The structure of a thallus includes three main parts. First, the holdfast is a root-like mass. It anchors the kelp to the sea floor. However, it does not absorb nutrients like true plant roots do. Second, the stipe acts like a stalk. It extends vertically from the holdfast to provide support. Third, the fronds are leaf-like attachments. These fronds are the sites for nutrient uptake and photosynthesis. Many species also have pneumatocysts. These are gas-filled bladders that provide buoyancy. They help the kelp stay upright in the water column.

Kelp forests are organized into different layers or guilds. Canopy kelps are the largest species. They often create floating layers that reach the ocean surface. Stipitate kelps extend a few meters above the sea floor. They often grow in very dense groups. Prostrate kelp species lie low along the ocean bottom. Below these, a benthic assemblage exists. This includes other algae and organisms living on the seafloor. This structure creates microenvironments. There is a sunny canopy, a shaded middle, and a dark seafloor.

Different genera of kelp live in specific global regions. Macrocystis, or giant kelp, grows in the Pacific Ocean. It can grow 30 to 60 centimeters vertically in one day. Laminaria is common in the Atlantic Ocean and near China and Japan. Ecklonia is found in Australia, New Zealand, and South Africa. The northeastern Pacific has the highest diversity. It contains more than 20 species from California to Alaska. Most kelp avoid tropical waters because they lack nutrients. However, scientists found thriving kelp in the deep waters of the Galapagos Islands.

Scientists study kelp forests to understand trophic ecology. This is the study of how energy moves through food webs. There are two main types of ecological processes. Bottom-up processes are driven by abiotic factors. These include light and nutrients like nitrogen and phosphorus. Oceanographic upwelling helps this process. Upwelling brings cool, nutrient-rich water to the surface. This allows kelp to grow rapidly. This growth then supports herbivores and larger consumers.

Top-down processes involve predators controlling the ecosystem. A famous example occurs in Alaskan kelp forests. Sea otters are a keystone species here. They eat herbivorous sea urchins. If otters are removed, urchin populations grow too large. These urchins then overgraze the kelp. This can turn a lush forest into a barren landscape. This loss of structure affects many other species. Many animals rely on the kelp for protection or food.

Human activities can cause significant kelp forest degradation. Overfishing is a major concern for nearshore ecosystems. Removing certain fish can release herbivores from population regulation. This leads to more grazing on the kelp. Climate change also affects these environments. In places like Tasmania and Northern California, kelp forests have nearly disappeared. To help, humans use marine protected areas. These areas limit fishing impacts. They also help buffer the ecosystem from other environmental stressors.