Kelp forests are similar to forest ecosystems on land, and are thought to have first appeared about 23 million years ago. Despite their similar appearance to plants, kelps are large algae, known as macro-algae. Some species can reach heights of 150 feet (45 m), and under perfect underwater conditions, can grow 18 inches (45 cm) in a single day. They grow in large, dense groups and host a wide variety of marine biodiversity. These forests also provide nesting, spawning and feeding grounds for many fish and marine invertebrate species. These underwater forests are some of the most dynamic and ecologically productive marine habitats in the world, occurring in colder ocean waters. Kelp thrives in nutrient-rich waters, and because they require sunlight to generate food and energy, kelp forests are always coastal and require shallow, clear water.
A structure called a ‘holdfast’ fixes the kelp to the rocky seabed. The holdfast supports a long stipe that grows upward through the water column. At the top, a gas-filled bulb floats with tendrils that extend outward throughout the stalk. This complex shape and structure provides a habitat for many different marine species. Kelp forests are dynamic, meaning they can appear and disappear based on oceanic conditions and the population sizes of marine herbivores.
Large kelp forests are important producers of oxygen, and they assist with sequestering carbon from the atmosphere. Researchers estimate that densely grown kelp forests are possibly more productive at removing carbon from the atmosphere than similarly sized forested areas on land. These forests also protect coastlines from erosion by breaking the flow of water.
Kelp forests provide ecosystem services to humans, including the fishing industry, ecotourism and the production of kelp bio-products. Therefore, not only are kelp forests important for marine creatures, they are also important for the health of humans and the planet. Unfortunately, we are at risk of losing large swathes of these underwater forests.
Species interactions within the kelp forest
Since kelp forests host a great marine biodiversity, they are also the home to thousands of interactions between different marine species. Should one species be removed from or introduced to the system, the entire system could collapse. Due to human impact, such as overfishing and unsustainable harvesting of marine resources, kelp forest food webs are constantly being altered by the loss of keystone species, such as sea stars, rockfishes, sea otters and seals.
The waters are warming
It is well-known that the world’s oceans are warming. Warm waters cause direct problems for many marine species – most notably resulting in the bleaching of coral reefs – but one of the significant indirect impacts is the resulting interactions between species. As waters are warming, species start to migrate to water within their preferred temperature range. Researchers have found evidence of predominantly poleward migration – meaning as the ocean temperatures rise, species are moving towards the cooler waters of the north and south pole. As species migrate to these new areas, they interact with established species that they have never interacted with before. These resultant interactions have a major impact on both the established species and the migratory species. Herbivores, such as urchins, and some tropical fish that can overgraze on kelp, are traveling south towards cooler waters, and are having a devastating impact on kelp forests.
Sea Urchins are destroying entire forests
Due to a phenomenon called “Sea Star Wasting Disease”, sea star species within kept forests are disappearing. Although scientists are still unable to determine what is causing the disease – or even if it is a disease at all – the disappearance of predatory sea stars are allowing their main prey, sea urchins, to flourish. Sea urchins have a voracious appetite for kelp and other algae, and without sea stars to predate on the urchins, their numbers are increasing exponentially. Despite their appearance, urchins are able to move swiftly across the seabed, grazing on kelp holdfasts and stipes. They are able to breed quickly, and are destroying entire kelp forests in their wake. This is resulting in what is known as ‘urchin barrens’ – oceanic dead zones where no kelp is able to survive. Once urchin barrens are established, it is difficult for kelp to reclaim the area, even if the urchins are removed. Some urchins are so good at feeding on the rocky substrate that even a small number of urchins can maintain a large barren. The resultant chain reaction on other marine species is catastrophic, as an entire habitat and ecosystem is lost.
Tropical fish and kelp forests
An Australian study published by the University of New South Wales has found that a small increase in ocean temperature can result in kelp deforestation. The kelp is not directly affected by the rising temperature, but hungry tropical fish are entering the kelp forests in search of food. The study found that the proportion of kelp showing signs of predation from fish increased from 10% in 2002 to 70% in 2008, while the proportion of tropical fish in the same ecosystem increased from 10% to more than 30%. Kelp was unable from regenerating due to fish feeding on the regrowth.
Other threats to Kelp Forests
Unfortunately, sea urchins and tropical fish are not the only threats to kelp forests. Human activity such as overfishing, pollution and climate change are directly and indirectly impacting on these underwater habitats. Runoff from agricultural areas, including pesticides, herbicides and other pollutants, are entering our oceans and can be damaging to these important and fragile ecosystems. Climate change and increasing ocean temperatures also promise to pose a threat to kelp forests, as kelp and other macro-algae is predominantly found in colder waters, and may not be able to adapt and evolve. Along with warmer water, climate change also brings more severe and frequent storms, which can be very destructive to these underwater forests. Severe storms can wipe out large areas of kelp forest by ripping the kelp from the seafloor.
These diverse and complex underwater ecosystems are key to the survival of many species in our oceans, and it is thus critical that they are protected. Organizations like Mission Blue have been working to place protections on kelp forests, and thereby also protecting other marine species. Throughout the world, many projects have been enacted to attempt to restore kelp forests through methods such as kelp planting, removal of invasive species, and reintroduction of keystone species.