Conserving coastal habitats: a new synthesis of evidence for kelp

This blog post was written by Dr Anna Berthinussen, a consultant at Conservation First and a Conservation Evidence synopsis author

Beautiful, majestic, towering… these are not words most people would associate with seaweed, unless of course they have had the pleasure of observing the natural wonder of a kelp forest! These vast underwater habitats, which form in cool, nutrient-rich coastal waters, are comprised of dense stands of large brown seaweeds called kelps. Although kelp are classified as algae rather than ‘true plants’, they share some similarities in structure and function. For example, kelp anchor themselves with root-like ‘holdfasts’ to rocky surfaces on the seabed and have tall hard stalks (stipes) that grow towards the light and support leaf-like structures (blades). Kelp can also be incredibly fast-growing, with some species (such as the aptly named giant kelp Macrocystis pyrifera) growing up to 60 cm in a single day and reaching dizzying heights of over 45 m!

These hidden forests beneath the sea may be less conspicuous or less well-known than their terrestrial counterparts, but they certainly rival them in terms of their size, biodiversity and productivity. Kelp forests are found along 30% of the world’s coastlines, and recent research has shown that they can be larger and just as productive for sustaining life as the Amazon rainforest [1]. These underwater ecosystems provide crucial shelter, food and nursery grounds for a diverse array of marine life, including thousands of species of fish, invertebrates, marine mammals, and other algae. Humans have also used kelp for centuries as food, medicine, and fertiliser. Today, kelp and its derivatives (such as alginate, a thickening agent) are used in numerous products from pharmaceuticals and cosmetics to toothpaste and ice cream!

Kelp forests also provide many other vital ecosystem services. They act as natural coastal defences, buffering the impact of storms and protecting coastlines from erosion. They remove nutrient pollution from the marine environment, capture huge quantities of carbon from the atmosphere, and contribute significantly to fisheries and tourism. Recent research estimates that kelp forests generate approximately $500 billion annually in ecosystem services such as these [2]. However, kelp forests are threatened by rising sea temperatures, pollution, destructive fishing practices, and changes in nutrient availability and predation dynamics. In many areas, overgrazing by sea urchins has turned dense kelp forests into barren seascapes. Drastic kelp declines have been reported globally, with over 95% loss in some regions, prompting an urgent worldwide call for action [3].

A global evidence synthesis for kelp conservation

For kelp forest restoration to be effective, it is imperative to understand which interventions do and don’t work. To help answer these questions, we have produced a global synthesis of evidence for kelp conservation. This synthesis gathers, in one place, available studies testing the effectiveness of any kelp conservation action, with each piece of evidence summarized in a clear and concise paragraph.

The synthesis includes over 100 kelp genera, including those belonging to the order  Laminariales (often referred to as ‘true’ kelps), as well as other large seaweeds that are widely known as ‘kelp’ and provide similar ecological functions (orders Fucales, Tilopteridales and Desmarestiales). We have created a list of 127 potential conservation actions, which include anything from cultivating kelp in a laboratory to transplanting kelp and installing artificial reefs, and from creating protected areas to removing predatory sea urchins or reintroducing sea otters. To obtain the evidence, the Conservation Evidence project has carried out extensive systematic searches of the literature over many years. This included screening over 1.2 million publications within over 700 journals and report series, in 17 different languages [4].

The resulting synthesis includes 216 summaries from 110 publications, which provide evidence for the effects of 40 conservation actions, all of which are available in the searchable online Conservation Evidence database. You can also view the synthesised studies grouped by action in the spreadsheet below. We hope that this freely available resource will be a valuable asset to anyone working in kelp conservation. The synthesis also highlights actions for which there is insufficient evidence to assess effectiveness for kelp conservation –we found no evidence at all for 87 actions – therefore providing a framework for targeted research.

What comes next?

At present, the evidence synthesis for kelp conservation has been published as an online database rather than a full Conservation Evidence Synopsis. We are currently seeking financial support to broaden the scope of this synthesis to include other groups of subtidal, habitat-forming vegetation. This collation of evidence on the evidence of actions is urgently needed – to inform conservation practice and policy, and to guide research activity.

One such group is seagrasses: marine flowering plants that form expansive meadows in shallow coastal waters. Like kelp forests, seagrass meadows are highly productive and biodiverse habitats that provide similar ecosystem services, such as protecting coasts, reducing marine pollution, acting as carbon sinks, and providing critical shelter, food and nursery grounds for fish, invertebrates, sea turtles and birds. However, seagrass meadows face similar threats to kelp and are declining at an alarming rate [5].

We have already laid much of the groundwork for a full synthesis through systematic searches of the literature and the creation of a synopsis framework (including a comprehensive list of conservation actions). We have around 350 studies on seagrass conservation in our literature repository, which are ready and waiting to be read and summarized! We hope to be able to incorporate these studies into a full synthesis on Marine Vegetation Conservation in the near future.

If you think you can help us with this project, please get in touch!

This synthesis was made possible thanks to funding from The Dulverton Trust and Cartier for Nature.

References

[1] Pessarrodona A. et al. (2022) Global seaweed productivity. Science Advances, 8, 2465. https://doi.org/10.1126/sciadv.abn2465

[2] Eger A.M. et al. (2023) The value of ecosystem services in global marine kelp forests. Nature Communications, 14, 1894. https://doi.org/10.1038/s41467-023-37385-0

[3] Eger A. et al. (2024) The Kelp Forest Challenge: a collaborative global movement to protect and restore 4 million hectares of kelp forests. Journal of Applied Phycology, 36, 951–964. https://doi.org/10.1007/s10811-023-03103-y

[4] Sutherland W.J. et al. (2019) Building a tool to overcome barriers in research-implementation spaces: the Conservation Evidence database. Biological Conservation, 238, 108199. https://doi.org/10.1016/j.biocon.2019.108199

[5] Unsworth R.K. et al. (2019) Global challenges for seagrass conservation. Ambio, 48, 801–815. https://doi.org/10.1007/s13280-018-1115-y