Verónica Castro-AllendeThe world’s oceans are heating at unprecedented rates, with 2023 marking the first year that global sea temperatures surpassed 1°C above pre-industrial levels. These soaring temperatures are driving the rise of marine heatwaves, which are prolonged periods of exceptional sea surface heat. Coastal heatwaves, seen from South America to the North Atlantic, threaten marine ecosystems, fisheries, and coastal economies. In tropical regions, vital ecosystems like coral reefs and seagrass meadows are being decimated, disrupting fisheries and tourism industries. The UK, traditionally shielded from the worst, experienced its own coastal heatwave in June 2023. The heatwave, particularly strong in the southern North Sea and English Channel, raised temperatures by up to 1.5°C. More extreme events in the northeast North Sea saw spikes exceeding 3°C. The impact of these marine heatwaves varies significantly depending on timing and location, with both short-term effects like species die-offs and long-term consequences such as biodiversity loss. With marine heatwaves becoming more frequent, the UK must urgently invest in research and monitoring to protect its vulnerable marine life and blue economy from these worsening conditions.
The world’s oceans are warming at an alarming rate, with 2023 marking a important milestone. For the first time, international ocean temperatures surpassed 1°C above pre-industrial levels, triggering coastal heatwave events across both hemispheres.
These intense temperature spikes were visible from South America and Japan to the North Atlantic. As the climate crisis worsens, marine heatwaves are becoming more numerous and powerful, posing a serious threat to marine ecosystems, economies, and coastal communities worldwide.
What are coastal heatwaves?
Marine heatwaves occur when the sea surface experiences exceptionally high temperatures for at least five days. These heat events can range in size from brief localized hotspots to extensive ocean basins.
Some last for weeks, while some, in severe cases, continue for months or even years. These persistent temperature spikes frequently have disastrous effects on marine biodiversity and southern industries.
International impact on ecosystems and economies
The effects of marine heatwaves extend much beyond the ocean. In tropical regions, coral reefs—critical to marine life and coastal economies —have experienced widespread bleaching.
Tourism is seriously harmed by this coastal loss. Also, some fisheries around the world have been devastated, with mass fish die-offs or migrations disrupting regional economies and food supplies.
Marine heatwaves even destroy whole underground ecosystems, such as seagrass meadows and kelp forests. These habitats are crucial for capturing carbon and preventing climate change.
Their destruction threatens the planet’s ability to regulate the climate and threatens its reliance on biodiversity.
Rising marine heatwaves in the UK
The worst marine heatwaves seen in different parts of the world have usually been avoided for the UK. But, in June 2023, the UK experienced a quick but intense marine heatwave around its shores.
The whole scope of the damage is still unknown, which calls for more research into the possible effects of such events on UK marine ecosystems and the blue economy despite being widely reported in the media.
Recent research from Frontiers in Marine Science has discovered that UK marine heatwaves vary depending on region. The southern North Sea and English Channel experience more, fairly severe heatwaves, with sea temperatures rising up to 1.5°C above average.
On the other hand, events in the northeast North Sea are shorter but more extreme, with temperatures exceeding 3°C above normal levels.
High variability in UK waters
Marine heatwaves around the UK vary considerably in terms of location, intensity, and duration. Some events have lasted up to five months and can occur year-round, also in winter.
This variability even affects natural responses. Research has shown that extreme sea temperatures do n’t always align with chlorophyll-a concentrations, a proxy for phytoplankton abundance, which adds complexity to understanding the biological effects of these heatwaves.
Ironically, the southern North Sea experiences more repeated’ greenwaves,’ periods of great phytoplankton productivity, while tropical regions are more prone to ‘ bluewaves,’ marked by low productivity.
However, there is still some variation in how genetic changes in the UK’s waters relate to temperature extremes, which warrants further investigation.
The role of seasonality
The impact of marine heatwaves is largely determined by the timing of their impact. When a heat wave hits during the summer, it can cause popular die-offs for species like seagrass and kelp that extend beyond their infrared limits.
However, a heat wave in the winter or spring could cause premature phytoplankton blooms, which could increase fisheries but also lead to harmful algal blooms.
Marine heatwaves have been linked to dangerously low oxygen levels close to the seabed in deep waters like the southwestern North Sea, which puts benthic ecosystems under severe stress.
This problem is particularly common in the second half of the year when the ocean floor’s effects are allowed to reach the effects of heatwaves.
Preparing for potential marine heatwaves
The UK is being issued a warning as a result of the June 2023 marine heatwave, which demonstrates that these incidents are getting more frequent and intense.
This is a significant opportunity for the UK to invest in research and monitoring to learn more about how coastal heatwaves will affect ecosystems, fisheries, and southern communities in the future.
The UK can learn from different countries and better prepare for the growing threat of marine heatwaves by identifying high-risk areas and strengthening the resilience of vulnerable species and industries.
These extraordinary events send a clear message that ocean health is deteriorating, and immediate action is required to safeguard both marine ecosystems and the ailing economies.
