Kelp forests
Kelp forests are large seaweeds (or macro algae), commonly found in temperate and polar oceans, but in 2007 they were also discovered in tropical waters near Ecuador. They occupy rocky habitats along the nutrient rich sub-littoral zone; part of the coast found at the end of the continental shelf that is always covered in water, despite the tide. Like trees of a terrestrial forest, species of kelp form a variety of habitats and are an extremely productive basal species for complex communities; making them hotspots for biodiversity.
Luscious green kelp forest at Catalina Island, California and Australian leafy sea dragons, Phycodurus eques
The morphology of kelp is simple. It has very little tissue specialisation which means the whole plant can photosynthesise and absorb nutrients. Air bladders draw the blades to the surface to maximise their exposure to sunlight, and the holdfast acts as an anchor to rocky substrate. The stipe is a stem like structure originating from the holdfast, giving rise to the fronds. Within the stipe are conductive tissues that allow nutrients from the upper parts of the algae to be transported to the lower parts. These tissues are unique to kelp. Along with planktonic algae, kelp is the primary producer of its ecosystem. Giant kelp grows up to 45cm per day, providing nutrients within and beyond its ecosystem.
The kelp forest community is shaped by the architecture of the brown algae, which forms three main horizontal layers. The forest floor is inhabited by sea urchins and sea stars, sheltered within the holdfasts. The fronds provide shelter and a feeding ground to many marine species of fish, crab and sea-dragons. The leafy sea-dragon is highly specialised at camouflaging itself against kelp fronds and crabs use the fronds to cling to, awaiting their prey. The canopy is the spawning ground and a sunlit, sheltered nursery for many important species of fish. Grebes dive for fish in the kelp forests and sea otters famously wrap themselves in the canopy fronds as they feed.
The problem
Kelp deforestation has been observed worldwide. Scientists estimate that giant kelp beds of eastern and south-eastern Tasmania declined by 95% between 1967 and 1997; thus illustrating the vulnerability of these habitats.
Ecosystem disturbance has had catastrophic effects on kelp forests. Indirect deforestation is ultimately caused by over-fishing of species that predate kelp herbivores. When predators are removed from an ecosystem, the populations of animals that would otherwise form their prey, are allowed to increase. In the case of kelp forests, the animals that tend to increase are those that feed on the kelp. Sea urchins (Echinoidea) feed on the holdfast and the blades. When their population increases, due to the removal of their predators (sea otter), kelp consumption can outweigh growth, resulting in ‘urchin barrens’, where kelp has been completely deforested. Predator species vary between kelp forests, but this effect of community structure disruption has been observed globally.
Direct deforestation for kelp is also a threat. In many countries there are laws in place to encourage sustainable harvesting of kelp, but often the ecosystem is still compromised. In California, 50% of a kelp canopy can be removed per day, threatening juvenile fish. Norwegian kelp forests are harvested on a 4-year rotational basis with a trawler, removing the kelp by its holdfast. In Norway, kelp forests are an important nursery for cod, but large scale removal of kelp forests frequently occurs. In part, this is likely to explain why cod is on the Norway red list of endangered species.
Demands for alginates are likely to increase as the human population rises. Increasing numbers of people are also migrating to coastal areas and so water pollution by contaminants, including toxicants and nutrient run-off, are likely to become more common. Furthermore, rising sea temperature is likely to cause changes in species abundance at different levels of the food chain; this will have serious impacts on the community structure.
Group of sea urchins and a diver amongst a kelp forest
The importance of kelp forests and why we should care
“…if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of kelp” – Charles Darwin, 1845
The species that depend on kelp are phyletically diverse; meaning they represent many different phyla (i.e. the rank that follows Kingdom in the taxonomic grouping system that is dependent on evolutionary relatedness). Kelp forests support ten or more animal phyla which is extremely significant, given that terrestrial forests have an average of 3 associated animal phyla. Fish stocks in the deeper ocean depend on the kelp forest canopy, which provides a sheltered nursery for many species, such as cod and wolf fish.
Kelp forests provide further supporting services to the outside biome, by regulating carbon. The International Union for Conservation of Nature (IUCN), suggests that kelp forests can store as much as 60 million tons of carbon that could otherwise contribute to oceanic acidification, or increasing atmospheric levels.
Kelp has a short lifecycle and it sheds its fronds frequently. This makes nutrients available to planktonic algae, which resides at the base of the food web, with kelp. This food web extends through numerous trophic levels, extending to higher vertebrates, such as birds and sea otters. Its nutrients are even transported to the lower seashore, which again demonstrates this ecosystem’s importance within its biome. Scientists have estimated that kelp forests are as productive as tropical rainforests and this productivity is reflected in the amount of species that exploit the kelp’s nutrients.
Kelp has been harvested by humans for millennia. Today, kelp provides alginates (a substance found in its cell walls), which are used in the manufacture of medicines and in food products. Additionally, the biodiversity and unique landscape of kelp forests make them a popular setting for divers and nature enthusiasts.
The solution: what we can do
Ultimately, the world’s government’s need to collaborate to protect our oceans and to then begin restoring damaged kelp forests. Marine Protected Areas (MPAs) are areas of the coast and ocean that are protected. They are an important conservation strategy and will help to protect the biodiversity of kelp forests. The United Nations Convention on Biodiversity (CBD), targeted global coverage of MPAs to reach 10% by 2020. It was hoped that this target would be reached by 2012, but efforts did not prevail. Please sign the Wildlife Trust’s petition, to raise awareness of the importance of MPAs. To learn more about MPAs, click here.
It is important that governments are made aware of the value of kelp forests as an ecosystem, so that they become a priority for the designation of MPAs. Kelp surveys are being carried out globally by volunteers ,so that scientists better understand the true value of kelp. The Californian kelp industry is believed to be worth up to $250 million per year, but kelp provides many ecosystem services which mean that it’s true economic value may be much greater. There are organisations encouraging participation in kelp surveys globally and residents of the UK can sign up here.
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