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UK seaweeds face an uncertain future in a warming ocean
The conservation status of Britain’s seaweeds has been revealed for the first time.
While just 7% are currently considered threatened, there’s simply not enough information to reveal the true picture.
Seaweeds are vital for health of our planet, but we are unaware of just how threatened they might be.
While we know that climate change, invasive species and pollution are having an impact on the marine macroalgae, the difficulty of studying them due to their wide range of lifestyles and shapes makes it hard to know the exact impacts on individual species.
A recent analysis looking to understand the conservation status of seaweeds in Britain faced this issue with over half of species considered to be ‘Data Deficient’, meaning there’s simply not enough information to know how at risk these algae are.
Professor Juliet Brodie, a seaweed specialist from the Natural History Museum who led the study, says, ‘Our analyses revealed that some very common species have experienced large declines, but because they’re so numerous they still appear to be abundant.’
‘We need to monitor seaweed populations in the long term so that we can identify when certain populations are declining, and why. More widely, a better understanding of seaweeds will ensure the continuation of vital marine ecosystems.’
The findings of the study were published in the journal Biodiversity and Conservation.
The coasts of Scotland are particularly rich in seaweed species. Image © Claire Pegrum, licensed under CC BY-SA 2.0 via Geograph.
What threats do seaweeds face?
With more than 644 different species identified so far, the waters around Britain are a hotspot for seaweeds. Researchers describe the UK’s coast as a ‘Goldilocks zone’ where conditions are just right for a wide range of different species to thrive.
Similar to corals in warmer waters, the most important role that seaweeds play is providing the structure of marine habitats. Seaweeds can provide shelter, food and support for a variety of different plants and animals, with kelp forests being particularly important around the UK.
‘Without seaweeds, life in the sea would be very different, and could be almost barren in places,’ Juliet says. ‘They have a key role in protecting coastal regions from storms and erosion as they form a protective barrier around the coastline that can dampen the effects of the waves.’
‘More importantly, however, they are fantastic primary producers in our seas, absorbing a lot of carbon from the atmosphere which drives marine ecosystems. They’re well adapted for this, and kelp forests are more productive than many ecosystems on land.’
These marine environments, however, are changing because of the climate crisis. To stay in their preferred temperature range seaweeds have been slowly moving poleward.
‘In the southwest, our main forest-forming kelp, Laminaria hyperborea, is declining in some places and other species are moving in from further south to fill those gaps,’ Juliet says. ‘While many arrivals are benign, the arrival of invasive species, such as wakame, could pose a risk to native species as they spread onto the shore and around the coast.’
Wakame (Undaria pinnatifida) is considered one of the worst invasive species in the world. Image © Juliet Brodie.
While the majority of Britain’s kelp forests are relatively secure for the moment, those in more southerly countries provide a warning of things to come. For example, Portuguese kelp forests have declined by as much as 70% as the oceans have become too warm for many species to survive.
As seaweeds decline, this reduces their ability to capture carbon, provide shelter, and provide other important ecosystem services.
Aside from temperature, carbon dioxide emissions also contribute to making the sea more acidic as carbon dioxide dissolves into the water. While some species appear to be quite resilient, calcifying seaweeds will suffer as levels of the minerals they need to grow decline.
Even fleshy seaweeds like bladder wrack, one of the most common species found along the UK’s coastline, might be affected. Recent research has shown that acidification makes this seaweed more fragile, making it more likely to break apart in stormy weather.
With such a wide array of threats facing them, it’s more important than ever to find out how seaweed species are faring. However, doing so is easier said than done.
As more carbon dioxide is emitted, kelp forests will become increasingly threatened. Image © Martin Prochazkacz/Shutterstock.
The difficulty in studying seaweeds
The gold standard in conservation is the International Union for the Conservation of Nature’s (IUCN) Red List, which is used to sort species based on their extinction risk, ranging from Extinct to Least Concern.
Two further categories, Not Evaluated and Data Deficient, are given to species that haven’t yet been assessed for the list or where there isn’t enough evidence to classify them.
For the seaweeds, which are often overlooked in favour of more charismatic marine species, this makes it a challenge to classify them. While Juliet’s paper found that only one seaweed recorded in Britain has become locally extinct and just 1% are Critically Endangered, this obscures the fact that 55% are Data Deficient.
These species might be in danger of extinction, but at the moment there simply isn’t enough evidence to say so. Part of the issue with this is the challenge of identifying different seaweed species.
‘The Red List has a series of criteria which focus on changes in certain aspects of a species,’ Juliet explains. ‘For instance, population reductions over a period of 10 years, or three generations, are one indicator that a species is under threat.’
‘Seaweeds, however, have a variety of distinct life stages that can reproduce sexually or asexually, and can look very different from one another. This makes it difficult to classify them based on generation time.’
Identifying a species is a particular problem, as has been highlighted by the Big Seaweed Search. This community science project asks members of the public to photograph the seaweeds they find in their local area, but around 15% of submissions misidentify the species. For some species, the misidentification rate can be as high as 90%.
Some seaweeds form calcified crusts on rocks, rather than growing into fleshy forms. Image © Juliet Brodie.
While mistakes can be corrected, it raises the question of how accurate historical records are, which are critical to provide the baseline data which can be used to track how a species’ distribution or population may have changed over time.
‘Around 50 of the UK’s seaweed species have only ever been seen when they were collected, while 36 haven’t been seen for over a century,’ Juliet says. ‘While this could mean that these species are now extinct, it could be that they’ve simply been misidentified or overlooked.’
To help address these concerns, Juliet and her co-authors have called for a concerted effort to study seaweed around the globe. This will help to build up the data needed to classify more seaweeds on the Red List.
Even then, it’s unlikely that this will fully address all the issues. It’s possible that the Red List criteria may have to be adjusted for ‘non-standard’ groups like seaweeds so that their extinction risk can be better understood.
As the conservation status of more seaweeds become known, this information could influence decisions about new marine protected areas, and direct targeted replanting of threatened populations. This will give seaweeds the best chance of surviving the turbulent centuries to come.
