How an Incease in Marine Heatwave Frequency is Impacting Ocean Dwellers and Marine Life

Our warming planet is now a fact of life. For centuries, abnormal temperature fluctuations have existed and affected our ecosystems. The ocean is one such ecosystem, delicate and easily damaged by increasing temperatures. Known as marine heatwaves, these events can devastate ocean populations and ecosystems around the world.

Are marine heatwaves becoming more common? Is there some way of preventing their deadly consequences? Here, we’ll take an in-depth look at what marine heatwaves are, what causes them, and the impact they have on marine life of all kinds.

Defining Marine Heatwaves

A term defined in 2011, marine heatwaves are abnormal, prolonged warmings occurring in seas around the world. To be classified as a marine heatwave, temperatures must increase beyond seasonal and annual records. In addition, these heat waves must extend beyond typical recorded temperature increases. 

While marine heatwaves refer to the warming of the ocean’s surface, these fluctuations are impactful enough to increase temperatures at lower depths. In fact, mean ocean temperatures are rising primarily due to climate change, although marine heatwaves contribute to short-term temperature spikes. Their frequency and duration have grown significantly, with a 54% increase from 1925-2016.

What Causes Marine Heatwaves?

Marine heatwaves occur due to shifts in atmospheric pressure, oceanic processes, and temperature advection. These extreme shifts are not necessarily abnormal; they’ve been a part of our seas since the beginning of time (think about El Niño years). However, the apparent increase in marine heatwaves is due to large-scale climate changes.

Rising surface sea temperatures have become commonplace for nearly 40% of the world’s oceans, influenced by increased greenhouse gas emissions. These increases bolster the properties at work in marine heatwaves, leading to more events annually as well as more extreme events altogether.

While attributing individual marine heatwaves directly to climate change can be complex, there is strong scientific evidence that climate change is increasing their frequency and intensity. Given that marine heatwaves occur naturally, especially alongside seasonal shifts, separating an abnormal event from a normal one is tricky. However, the overall increase and duration of marine heatwaves have scientists fearful for the ocean’s future.

Extreme Warm-Water Events Are Increasing

A defined framework for marine heatwaves exists thanks to an abnormal temperature increase off Australia’s western coastline in 2011. Scientists separate marine heatwaves from seasonal shifts when “temperatures exceed the 90th percentile of the local climatology for five days or more”. These high temperatures are happening more and more frequently — and for longer periods of time.

Warmer temperatures for longer durations have devastating effects on oceanic ecosystems. Marine heatwaves and rising surface temperatures are at the heart of many unexpected shifts in sea creatures, from mammals to corals and everything in between. 

The Impact of Marine Heatwaves on Ocean Ecosystems

Marine heatwaves don’t simply increase the temperatures of our seas. They harm the very foundations of all oceanic ecosystems. Here are some of the major impacts marine heatwaves have on our seas.

Coral Reef Bleaching

At the heart of nearly every ocean ecosystem are coral reefs, and they are devastated by marine heatwaves. Coral reef bleaching occurs during these impossible rises in temperature, leading to the deaths of entire reef communities. Scientifically speaking, the macroalgae covering coral reefs cannot survive the heat, typically taking the coral with it as it bleaches and decays.

Many coral reef activists and scientists are taking action against reefs with high levels of macroalgae. By decreasing its presence, corals are more resilient in the face of moderate heat waves. However, there’s still very little to be done for reefs facing global greenhouse gas emissions and widespread pollution.

Population Fluctuations

Marine heatwaves affect all life in the ocean, not just coral reefs. Studies find fish, bird, and planktivore populations fluctuating significantly after marine heatwaves. Some species thrive, experiencing huge bursts in their numbers. Others are not so lucky, especially plankton and other microscopic organisms. Entire species have been wiped out by marine heatwaves, leading to a complete and total imbalance in ocean ecosystems.

Migrating Species

Sea creatures who are able to migrate away from warmer waters do so in the face of marine heatwaves. Sea lions, shark species, and large fish such as tuna have all been observed migrating during harsh marine heatwave years. However, it isn’t necessarily a migration as it is a total displacement of these populations. As marine heatwaves increase, many ocean species face habitat loss and devastating ecosystem damage.

Socio-Economic Issues

As temperatures rise, the socio-economic consequences of marine heatwaves rise too. Many studies fear the increase in these events, as the economic losses can be dire. This report estimates that over $4 billion is lost annually due to marine heatwaves and their devastating consequences on commercial fishing, tourism-based industries, and foundational ocean species which support every underwater ecosystem.

A direct quote from this study indicates “Economic losses of single MHW (marine heatwave) events to date exceed US$800 million in direct losses and in excess of US$3.1 billion per annum in indirect losses for multiple consecutive years. The true costs are, however, likely to be much greater because many socioeconomic effects likely remain unknown and underreported, particularly in lower-income countries.”

What Can Be Done About Marine Heatwaves?

Given that marine heatwaves appear to be increasing in both duration and frequency due to climate change, very little can be done to limit their impact. Many studies suggest lessening the knowledge gap between humans and marine heatwaves, as awareness is the first necessary step. 

Discussing marine heatwaves as a socioeconomic issue may help shine some light on the topic. While highlighting ocean ecosystem decline should be enough for the world to take action, couching these warming events in an economic framework should lead to further concern.

However, marine heatwaves aren’t going anywhere. In fact, their upward trend has scientists, activists, and ocean lovers seeking answers. Ultimately, reducing emissions, relying on renewable energy, and developing accurate heatwave warning systems are the only potential solutions currently available. 

Adapting to Marine Heatwaves: An Uncertain Future

There’s a great deal left to learn when it comes to marine heatwaves and climate change. However, one thing is certain: our planet faces an uncertain future should the oceans continue to warm. Only time and swift action can lessen the impact marine heatwaves have on our seas. Perhaps positive changes will occur before our varied, precious ecosystems face extinction.