How is climate change affecting what we see underwater in the UK , asks Becky Hitchin
BECKYHITCHIN
Babakina anhedonia Pleurobranchaea britannica
This week ’ s highlight was the news of a new nudibranch found in the UK , Pleurobranchaea britannica . This follows the discovery of the rainbow-coloured slug Babakina anhedonia in the same area in 2023 , typically seen in the warmer waters off the coasts of Spain , Portugal and France . Several other nudibranchs have also recently been found around the UK that are better known from warmer waters .
Climate change is inherent in these new appearances of small sea slugs . The seas around the British Isles , and in particular , the southern North Sea have been identified as one of 20 global areas that have warmed the fastest over the past 50 years . UK sea levels have risen by an average of 12-16cm since 1900 , and sea temperatures are continuing to rise , by 0.4 % per decade .
As a result of these warmer temperatures , concentrations of dissolved oxygen decrease , compounded by increasing acidity and falling levels of salinity . This triple whammy has huge knock-on effects for a wide range of organisms . Sea surface temperature change affects different sized organisms differently . Small infaunal creatures [ those that live in soft sediment ] tend not to show such a change , as increased availability of food associated with the temperature increase helps damp the effect .
Larger organisms , however , experience changed community structures due to increased competition for food . This affects both plants and animals . The latest review by the Marine Climate Change Impacts Pathway suggests that North Sea burrowing species have both shifted their distributions in response to changing sea temperature , and have needed to try to become adapted to warmer temperature than they were previously exposed to . This has led to decreases in vital rates and changes in behaviour .
All change in our shallow seas
How is climate change affecting what we see underwater in the UK , asks Becky Hitchin
The Marine Climate Change Impacts Pathway highlights a case of kelp changes associated with sea surface temperatures . Laminaria ochroleuca , the golden kelp , has increased in abundance and expanded its distribution into more wave-exposed conditions from its original warmer water conditions . Why does this matter ? Well , each species of kelp is slightly different .
Colder water kelps such as L . digitata and L . hyperborea , the standard kelps we see in very shallow UK waters , host a huge amount of other species on their stems and blades . All divers have marvelled at the amount of life on the subtidal kelps – after all , what else are shore dive safety stops for ? Bryozoans , red seaweeds , hydroids , all sorts of molluscs graze on that carpet of organisms attached to kelp . Golden kelp , however does not . This lack of three dimensional community
While warm water species incursions in the south , cold water animals such as the wolf fish retreat north
structure leads to changes in structural changes in ecosystems as well as changes in how ecosystems function .
Scientists also looked at the angular crab , Goneplax rhomboides . They found that the crab has been moving into the Moray Firth and further , into the southern North Sea , driven by increased sea surface temperature – in this case , the North Sea becoming warmer and more available to species that historically have lived only in warmer climates .
Also changing are the UK fish stocks . Cefas , a UK agency working to ensure a sustainable future for our rivers , seas and the ocean , has recently shown that warmer seas are already having an impact on fish stocks around the UK . Warm water species are increasing , such as anchovy , bluefin tuna , squid and red mullet .
The number of bluefin tuna around the south coast of the UK is now at such a level that the UK
“ Sea surface temperature change affects different sized organisms differently ” government has created a stock quota for the fishery . In parallel , coldwater species are seen to be retreating . These include such charismatic species such as wolf-fish and Atlantic cod .
These are only some examples . It would be good to hear local experiences of how our seas are changing . What species are new ? What normal creatures have become rare ? How is climate change affecting your diving ? �
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