Marine Heatwaves: What Are They? 
In recent news, the rise of marine temperature has become a popular conversation and for good reason too. Put simply, sea surface temperatures around the UK and Ireland in recent months have been markedly higher than we expect for this time of year. According to the data from the Met Office, the temperatures being recorded are the highest since records began in 1850.

Causes of Temperature Rise

There are likely to be multiple environmental factors involved. Some of these are that it’s an El Nino year – when rising sea surface temperatures in the Pacific influence temperature rises elsewhere; there is thought to be less Saharan dust in the Northeastern Atlantic atmosphere this year (which generally has a cooling effect), and; increasing temperatures generally due to climate change.

Oil rig stock image with sunset

Why It Matters
The temperature of the seawater directly affects the organisms living in it. Different species tend to live in temperature niches which they are biologically suited to. If temperatures get too hot or too cold, then these can be harmful for the organisms. This is why as sea temperatures rise, we expect to see more pelagic fish species in our waters that we would normally expect in more southerly, traditionally warmer waters.

For example, our Director of Fisheries & Research, Dr Ryan Mowat, recently saw a sunfish off the coast of Brighton on a diving trip! – totally unexpected (or is it the new norm?)

This is becoming a more common occurrence generally. In the case of a marine heatwave though, the worry is that the sudden unexpected spike in temperatures might lead to mortality events amongst resident species. We’re not seeing evidence of that in the UK just yet.

In the long run higher temperatures are a concern as species habitat ranges will change and this is particularly problematic for less mobile species such as oysters, kelp and seagrass. There are important restoration programs underway in the UK aimed at these groups and increasing marine heatwaves could harm these.

Underwater shot of sea kelp

Harmful Algal Blooms (HABs) 
One noticeable effect of higher seawater temperatures is the occurrence of harmful algal blooms (HABs). HAB detection and mitigation is something we get asked about regularly by UK aquaculture producers. They occur when phytoplankton species reproduce rapidly in sea surface waters when conditions are suitable, with higher temperatures being a key driver. Clouds of phytoplankton can lead to drops in water oxygen levels and some of these plankton can produce toxic chemicals that are harmful to the health of people and animals. When HABs get pushed by tidal currents through shellfish and salmon farms the effect can be ecologically and economically devastating. Read more about HABs here.


What’s Next for Science?
The UK’s coastal seawater temperatures are continually measured by government agencies such as the Centre for Environment, Fisheries & Aquaculture Science (CEFAS).

Other citizen science projects highlight the importance of getting involved with sampling and recording scientific data at a public level. At RS Aqua we recently sponsored a fantastic project called the GB Row Challenge, notoriously known as the toughest rowing challenge in the world.

GB Row runs annually, with the teams involved rowing 2000 miles around the coastline of Great Britain nonstop. At the same time, they are continually collecting valuable samples of environmental data, such as sea surface temperature, microplastics, eDNA and underwater noise recordings.

Water quality monitoring will arguably need to increase on a larger scale in future years to support the level of research needed.

Sewage pipe in UK waters

How You Can Get Involved…

There are loads of exciting ways you can get involved in logging and recording sightings of marine species in coastal waters and on beaches. Some examples include iRecord, Kelp Recording Scheme, Seasearch & Shoresearch, and many more.

The more individuals engage with these initiatives, the more data scientists have on how the marine environment is changing and how species habitat ranges are being affected by rising temperatures.

For more resources, we recommend getting in contact with your local Wildlife Trust.

Student in biology taking sample of natural water

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