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National Marine Week: Climate change & moving species ranges

©️ Penny Dixie

For National Marine Week, some of our Coastal & Marine interns were inspired to write a blog about climate change and moving species ranges. Read their thoughts and research on all things sea level rise and changing climate patterns.

How is climate change affecting species’ movement? 

Climate change is expected to lead to warmer seas, sea level rise, increased flood and drought frequency, and ocean acidification.

Our oceans are changing:

  • Sea surface temperature: Global sea surface temperatures reached a record high in February 2024 of 21.06 °C between 60°S–60°N 
  • Sea level rise: The sea has risen by an average of 4.5 millimetres/year between 2013 – 2021
  • Ocean deoxygenation: Oxygen levels are expected to decrease by 3-4% by 2100 
  • Ocean acidification: PH has decreased by 0.1 units. This may not seem like much but the pH scale is logarithmic which means that the pH has dropped by 30% since the pre-industrial era.

Alongside these shifts in our climate patterns, there are changes in the underwater ecosystem. Increased warming, loss of oxygen and change in pH, tests the physiological limits of marine species. These changes may be happening at a rate that marine life cannot adapt to.

Increased magnitude and frequency of stressors means organisms’ tolerance limits are tested. Changes in sea surface temperature, sea level rise, oxygen levels, and pH levels will affect how marine life is able to deal with their conditions.

Increasing sea surface temperatures and marine heatwave frequency threatens mussels’ thermal limits. As sea levels are rising due to the combination of glaciers melting and increased flooding, this may lead to lower salinities. Increasing temperatures and lower salinities could affect the physiology of the organisms and potentially disrupt cellular processes. Just like your body deals with the stress of being out in the sun for a while or not drinking enough water – the bodies of marine organisms get stressed too.

Increasing ocean temperatures are also impacting oxygen availability. In warmer water there is less oxygen, and the warmer water is more buoyant. This results in less mixing of the oxygen-rich surface water to deeper waters which decreases oxygen availability. On top of this, in warmer waters, organisms require more oxygen. Imagine being in a hot climate and not being able to breathe.

Ocean acidification, due to rising CO2 levels, is an environmental stressor that is a bit harder to picture. More acidic environments impact organisms' ability to build structural integrity. For example, our beautiful corals may not be able to build their structures. Existing shells, such as that of a mollusc, may even begin to dissolve.

These drivers may all act as single stressors, but it should be recognised that the simultaneous effects of multiple stressors could be positive or negative. To stay in an area aligning with their required conditions, species must: adapt or move. 

How is climate change driving a migration of species?

It is amazing how nature finds a way- one way of dealing with these environmental stressors is to: just keep swimming. What is meant by this? Some species are migrating to more favourable regions. For example, there has been a documented migration of species to higher latitudes.  

Annual latitude change graphs

Figure 1. Graphs showing the annual change in latitude (movement in miles and depth (feet) of 41 marine species along the Northeast coast, 58 marine species in the Bering Sea, and 58 marine species along the Southeast coast. The multi-region average consists of 157 unique species. Changes in the centers of biomass have been aggregated across all species and by region. For each region, the change in latitude and change in depth are set at zero for the base year 1989. (NOAA, 2024). Data source: NOAA (National Oceanic and Atmospheric Administration). (2024). DisMAP data records. Distribution Mapping and Analysis Portal. Retrieved May 6, 2024, from https://apps-st.fisheries.noaa.gov/dismap/DisMAP.html

In addition to environmental changes altering suitable conditions (i.e. temperature and oxygen), habitat loss and prey movement can also drive species’ migration. As sea temperatures rise, fish have begun migrating poleward or to deeper water to reach colder regions which are more favourable.

Changes in conditions have impacted ecological communities. Habitat-forming species have been impacted by these changes. We have heard of the threats of coral bleaching but closer to home climate change is also threatening seagrass meadows, oyster reefs and kelp forests. These are all vital habitats that support a variety of marine species. Seagrass meadows, for example, are nursery grounds for many juvenile fish and are a biodiversity hotspot. Charismatic seahorses hide in seagrasses too!

This begs the question: Where do you go when your home disappears?

In our local community in Kent, we can see non-native species changing the habitats as well. Pacific oysters and mussel beds are competing for space and pacific oysters are forming on mudflats and chalk reefs. All these changes can cause loss in the suitability of the original habitat, altering the ecological community, and rearranging the food web.

A juvenile oyster attached to a mussel shell.

©️ North East Kent Scientific Coastal Advisory Group

Movement of prey is another driver of species’ migration. For example, the location of oceanic white tip sharks is impacted by the quantity and distribution of their prey. For predators, there may be plenty of fish in the sea- but they’re not always where they used to be!

Our beloved and charismatic marine mammals are an example of species appearing in parts of the world where they haven’t been before. As temperature conditions have shifted, and prey distribution has altered, different regions are now more suitable for these species. In the UK, we have seen an increase in strandings of warm water adapted cetaceans, such as common dolphins, short-beaked dolphins and striped dolphins. Meanwhile, there has been a decrease in cold-water species, such as Atlantic white-sided and white-beaked dolphins in the same regions. This displays a shift in the distribution of these UK marine mammals in connection to limited habitat availability.

A single dolphin breaching out of water.

©️ Chris Gomersall/2020VISION

How might you notice these changes?

In the UK, we might notice changes in species’ ranges on our plate- particularly if you’re a fan of fish and chips!

A report published by Cefas highlighted that commercially important fish species, such as Atlantic cod or haddock, are currently, and will continue to, experience a decrease in UK suitable habitat due to warming waters. Specifically, they are predicted to display a substantial northward shift by 2060. This is likely driven by Cod’s narrow thermal limits, meaning warmer waters can reduce cod foraging activity, sexual development and spawning time. Additionally, the northward distributional shift could also be driven by cod following the movement of their prey. In fact, fishers in Kent have stated that Cod fishing has not been successful, or even completely impossible, for over 10 years.

For UK fishers, this presents a challenge: as their target species move northward, some boats may have to travel further distances to fulfil their quotas. What’s more, some fishers may experience a reduction in catch if species’ distributions move across political boundaries. These climate impacts will therefore increase pressures on the UK fishing industry.
 

A fishing boat out at sea on a grey day.

©️ Chris Gomersall/2020VISION

However, just as cod and haddock are experiencing a decrease in suitable habitat within the UK, common southern European species, such as European seabass, anchovies, and sardines, are forecast to experience an increase. Their distributions are anticipated to shift from northern France to the Irish Sea and central North Sea. This presents new opportunities to the commercial fishing industry. Already, summer squid fisheries in north-east Scotland are taking advantage of the greater abundance of squid. However, this northward distributional shift of key commercial species means our fish and chip order is becoming more difficult to locally source. This in turn forces the UK to import our favourite species, like cod, haddock, and scampi, from elsewhere.

How can you get involved?

Along the Kent coastline, you might notice some of these changes first hand. Due to warming water temperatures, some species may become increasingly common and easier to spot as their distributional ranges expand.

Beachgoers could see more spider crabs in the future, which are becoming more abundant in South Kent. This follows increasingly frequent mass sightings along the Cornish coast as a direct result of warming waters. Similarly, rock poolers might also find more strawberry anemones. This southern species is displaying a shift from Sussex towards the Kent coastline, as the eastern waters warm and become more suitable for their life processes. 
 

A mass of spider crabs on the sea bed.

©️ Alexander Mustard/2020VISION

Unfortunately, the reverse is also true. Over the last 2-3 decades, Kelp has become a much less common sight, as warming waters can disrupt growth and cause heat stress.  If you have been living in Kent for a while, you might have noticed these changes yourself.

In response, the Wildlife Trust has volunteer Shoresearch teams, working to record essential data on the UK coastline’s flora and fauna. Shoresearch helps monitor species found in these habitats, providing crucial insight into the effects of climate change, pollution and invasive species. And you can get involved! 
 

Volunteering

Toby Roxburgh/2020VISION

This is an excellent opportunity to get stuck into some citizen science, providing invaluable data which helps us understand climate threats much better- for example, how climate change affects species’ ranges. If you’re more interested in just learning about the coastline, or you have little ones in tow, you can also get involved with rockpooling! Follow the links below to find out more about how to get involved and make an impact yourself:

Find out about volunteering with Shoresearch in Kent

A handy guide to help you rock pool safely

‘Beneath the Water’ guide for indicator marine species to look out for in intertidal zones

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