- Kelp forests grow along more than a quarter of the world's coastal strips and constitute one of the largest ecosystems on the planet in terms of biodiversity. However, these key habitats are disappearing due to warming oceans and other effects caused by humans.
- The recent sudden disappearances of vast kelp forests along the coastal strips of Tasmania and California have highlighted how little we know about protecting or restoring these essential marine ecosystems.
- Scientists are looking for new ways to help kelp recover but promising small-scale successes need to be significantly developed to address massive kelp losses in some regions.
- Global interest in studying algae for food, carbon dioxide storage, and other uses may help improve ways of reintroducing kelp into the wild.
Hidden underwater, kelp forests grow along more than a quarter of all coastal strips in the world, fostering biodiversity so rich that naturalist Charles Darwin believed it could rival tropical rainforests. Equally invisibly, these critically important habitats are disappearing due to warming ocean currents, pollution, overharvesting, and other human-caused effects.
While knowledge has been gained from kelp cultivation in Pacific Rim countries over the centuries, regional declines in kelp forests and recent sudden disappearances from large areas where kelp once thrived have highlighted how little conservationists know about protecting or restoring these critical underwater forests, says Karen Filbee-Dexter, a marine ecologist at the University of Western Australia who studies the impact of climate change on kelp.
“Kelp forests are underreported and understudied compared to other coastal ecosystems,” says Filbee-Dexter. “We need to understand them better. They constitute one of the largest plant habitats for marine species on Earth and the data show very clearly that they are changing very rapidly”.
The first alarm bells for researchers were marine heat waves that suddenly devastated entire kelp forests along the coast of Tasmania in 2011 and Northern California in 2014. As the towering thalli and blades of kelp disappeared, so did many of the marine species they supported for sustenance. With the disappearance of fish, abalone, and lobster, they have had to close the commercial fisheries with a turnover of several million euros. In addition, the loss of extensive kelp forests reduces the protection afforded to coastal communities against storm surges and eliminates an important carbon sink. Scientists believe that the world's kelp forests store between 61 and 268 teragrams (61 to 268 megatonnes) of carbon per year.
The good news is that scientists are finding ways to successfully reintroduce algae. However, these newly discovered methodologies need to be developed considerably (and rapidly) to compensate for the massive losses that have occurred in some regions, such as Australia, Norway, Nova Scotia (Canada) and California (USA).
The challenges of scientific kelp management
Kelp has been in the news lately due to its remarkable carbon sequestration capacity. So far, most of the attention has been on cultivated kelp, but whether it is wild or cultivated, what scientists are discovering could help all types of kelp thrive in a world of rapid climate change.
There are over 100 species of kelp (large brown algae that live in cold, deep waters around the world), but most studies so far have focused on just two varieties: the endangered giant kelp macroalgae which form vaults in the water ( Macrocystis pyrifera ) and the nematocysts ( Nereocystis luetkeana ). These dense underwater forests can grow rapidly up to 40 meters in height, creating a complex habitat that extends from the seabed to the surface of the sea.
Some of the underlying causes of forest decline are clear. Currents that warm the oceans and marine heat waves, for example, push kelp, which usually lives in cold waters, out of their physiological comfort zone if the water temperature rises above 20 °C, in which case they die. Coastal development, pollution, and sedimentation, which worsen water quality, increase the challenges for their survival. However, it is not always clear why stressed kelp disappears in some places but still thrives in others.
This is partly due to the difficulties involved in studying such forests. Often it can even be difficult to find them. In the past, kelp forests were detected by ships, small planes, and satellites. However, not much data is collected with these methods. Only the once-forming kelp is visible from the surface of the water, and although giant kelp is perennial, the nematocysts die off in winter and reappear in summer, making them difficult to spot. Kelp can also move: Severe storms can uproot entire forests overnight.
Accurate maps are essential for better management of these forests, as they provide warnings of declining forests as well as an essential baseline for monitoring recovery and restoration projects, says postdoctoral researcher Sara Hamilton who works in Davis for the University of California. Without a real assessment of the situation, it is also difficult to regulate the harvesting of wild seaweed for commercial purposes in a sustainable way.
Worldwide, according to 2019 data from the Food and Agriculture Organization of the United Nations, over one million tonnes of kelp is harvested each year. Much of it, around 40 percent, is harvested off the coast of Chile, with wild brown algae being marketed for various purposes such as biotech uses and food production as well as pharmaceuticals and textiles.
Countries that regulate kelp harvesting often set maximum annual amounts of biomass that can be harvested, but regulations can also pose problems. When Hamilton analyzed the management of kelp crops in Chile, California, and British Columbia (Canada), he found that the absence of a regularly updated kelp inventory in all three areas constitutes a "significant obstacle" to effective management.
“There is good research in the literature focusing on kelp forest life but we need to go one step further and gain scientific insights into how we can manage them effectively,” says Hamilton.
For example, in Chile, the harvesting of seaweed is governed by a complex set of management systems including marine protected areas where harvesting is prohibited, i.e. exclusive access areas controlled by consortia of local fishermen, and open access areas unprotected. Tracking kelp across crops may not always be accurate, Hamilton notes.
Also, scientists don't know exactly how much kelp can be harvested before forests are too weakened to grow again. Although the amount of kelp harvested in California and British Columbia is much lower than in Chile, Hamilton says regulators in those areas rely on self-reports for commercial harvesting, which may not be reliable, and only loosely track recreational collection activities (which create large data gaps) that are performed for personal purposes.
Similar to the conclusions of the Hamilton analysis, in the United States, the California Department of Fisheries and Wildlife published 2022 a report on the improvement of the situation on neroocysts and giant kelps including recommendations for more accurate monitoring and a better understanding of the impacts of harvesting activities as well as the roles of the main predators living in kelp forests. Similar environmental concerns have led to a new law in Washington State (US) aimed at protecting and restoring approximately 4,000 hectares of nematocyst forests and seagrass meadows by 2040.
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