by Jules B. Kajtar, Senior Research Scientist – Physical Oceanography, National Oceanography Centre, and Zoe Jacobs, Biogeochemical Modeller, National Oceanography Centre, University of Southampton
A dip in the sea can provide welcome relief after long stretches of hot weather — especially when the water is an inviting 20°C or more, as it has been recently across southern parts of the UK. But such sea temperatures are unusually warm, with UK waters being hit by the third major marine heatwave in four years.
Aside from obvious negative consequences for people, such as more drownings in open water, marine heatwaves can affect sea life of all sizes, from microscopic plankton to huge whales.
Around the world, such instances of unusually warm sea temperatures for five days or more have caused die-back of key species such as kelp, seagrass and corals.
Marine heatwaves have also caused death or changes to the life cycles of marine mammals and shellfish, as well as other species that depend on them, such as seabirds. They have caused species to migrate or shift their geographic range. These changes all disrupt ecosystems, with disastrous ramifications for oceanic food webs.
Kelp forests and seagrass meadows normally provide crucial nursery habitat for young fish and shellfish. But they are also under threat from marine heatwaves, as warmer waters hinder their ability to provide refuge for marine species.
Because of changes to fisheries and ocean health, marine heatwaves have huge social and economic consequences. In Western Australia, the consistently warm seas led to the coining of the term “marine heatwave” in 2011. This caused decimation of seagrass meadows, along with die-back of kelp, corals, fish, abalone, prawns and crabs. Some parts of that marine ecosystem took years to recover; other parts have never bounced back.
Now, the race is on to understand the knock-on effects of marine heatwaves and which marine species are most threatened. Management interventions, such as harvest strategies or catch quotas, can protect breeding populations and young fish, helping to maintain healthy fish and shellfish numbers. The earlier these interventions are implemented, the better.
This article is republished from The Conversation under a Creative Commons license.
