The Effects of Marine Heatwaves on Aquatic Ecosystems

The Effects of Marine Heatwaves on Aquatic Ecosystems

Iman Kashif - 13 August 2021

What is a marine heatwave? Simply put, a marine heatwave describes the irregular occurrence of extremely high temperatures within the ocean. Marine heatwaves can be compared to a heatwave on land, but instead have effects on aquatic ecosystems as opposed to land ecosystems.

Over the Years

Dating back to 2013, the prevalence of marine heatwaves occurring in recent years can be actively tracked. “The Blob” refers to a specific marine heatwave which originated off the coast of Alaska in 2013, made its way to Mexico in 2014, and persisted well into 2015. In 2019, a marine heatwave was seen to have emerged in the Northeast Pacific, resembling “The Blob” from 2013. The emergence of the marine heatwave in 2019 sparked concerns, as it hinted to the possibility of the recurrence of the effects instated by the 2013 “Blob,” even leading the US federal cod fishery to close its doors for the 2020 fishing period as an extra measure due to already reported low numbers of Pacific cod.


Oceanic heat waves tend to happen due to abnormal patterns in weather which result in an increased amount of heat being driven into the ocean, instilled within the surface of the ocean, or block heat from exiting the ocean. Marine heatwaves can also be attributed to climate change, with climate change enabling the mere existence of marine heatwaves to be 20 times as likely than without global warming.

Direct Effects

Marine heatwaves have various negative impacts on aquatic organisms living in oceanic ecosystems, not limited to but including the following: coral reef bleaching, destruction of kelp and additional aquatic vegetation, and a reductive shift in reproduction/survival of many oceanic creatures.

Specifically within the West Coast, zooplankton was found to be significantly smaller in size according to NOAA (National Oceanic Atmospheric Administration) Research. This negatively affects aquatic animals that consume zooplankton, such as small fish or seabirds, due to the lack of calorie and fat content within the zooplankton.

Additionally, a relationship between the increased presence of marine heatwaves in relation to the increased presence of harmful algal blooms can also be examined. In 2013, a NCCOS (National Centres for Coastal Ocean Science)-sponsored study found that the recurrent marine heatwaves on the West Coast of the US directly resulted in an increase of detrimental algae, spreading every year since 2015. The aftermath consisted of the shutdown of harvesting shellfish and Dungeness crab. In regards to marine life, algal blooms have caused various aquatic mammals to become victims of eating contaminated fish and other poisoned substances. This was seen around summertime in the Puget Sound area according to Nick Bond, a scientist with a NOAA cooperative institution.

Harmful algae blooms pictured above