When conservation ecologist Rob Harcourt went surfing off Sydney, Australia, he immediately knew the water was warmer than usual.
“We had at least 23 [degrees Celsius, or 73° Fahrenheit] sea surface temperature,” Harcourt, a professor at Macquarie University, told Mongabay. “He’s normally around 18[°C, or 64°F] in November, December. So it’s 4 to 5 degrees warmer than normal. It’s huge.”
Last month, this marine heat wave, which began in November 2021, attracted international attention. Moninya Roughan, an oceanographer at the University of New South Wales, said The Guardian that the event was “extreme”, with hot water covering an area of about 200 square kilometers (77 square miles). Other experts have noted that the event could have a huge impact on a whole range of marine animals, including sharks that have traveled further south in search of food.
While this marine heat wave has moved slightly away from the coastline, meaning it will be less damaging to coastal ecosystems, there are still sea surface temperatures of around 25°C (77°F ) east of Sydney.
This marine heat wave is just one of many waves taking place in the world’s seas, from the Arctic Ocean to the Southern Ocean. In the region around Australia, marine heatwaves are also simmering off the coasts of the island state of Tasmania and the North Island of New Zealand. In fact, Alistair Hobday, research director and senior scientist at the Australian government’s Commonwealth Scientific and Industrial Research Organization (CSIRO), called the Sydney event “quite small” compared to other marine heatwaves. that occur in the world.
Marine heat waves, which can be defined as warming events in which sea temperatures exceed a certain threshold and last at least five days, can be triggered by a range of atmospheric, oceanic and climatic factors. Yet human-induced climate change has also played a prominent role in increasing the frequency and intensity of these heat waves, Roughan told Mongabay in an email.
“Think of it like the stock market on an uptrend, along the way you have a lot of highs (and lows), but those highs are increasing because of climate change,” Roughan said.
In 1982, only 60% of the oceans had experienced a marine heat wave. But by 2020, 80% of the oceans had experienced these events, according to Hobday.
Marine heat waves can have various implications on the marine environment, from coral bleaching to the redistribution of fish to the destruction of kelp forests. One of the most notable events occurred in the Pacific Northwest between 2014 and 2016, resulting in toxic algal blooms and mass marine fatalities. In 2016, a major marine heatwave also occurred in the Tasman Sea, leading to wild shellfish mortalities and outbreaks at oyster farms.
Tiger shark sightings (Galeocerdo cuvier) and whale sharks (Rhincodon type) off the coast of New South Wales are likely to have to do with the marine heat wave, says Vanessa Pirotta, wildlife scientist at Macquarie University.
“Many of these marine megafauna – the largest animals – their movements are mainly dictated by prey movements and prey distribution,” Pirotta told Mongabay. “So any change in environmental factors is likely to cause a change in their prey, which…will bring these animals down.”
As the ocean continues to warm due to human-induced climate change, experts say marine heatwaves will only grow in intensity and frequency.
‘We’re just waiting navy [heat] the waves will increase in the future,” Neil Holbrook, professor of ocean and climate dynamics at the University of Tasmania, told Mongabay. “We have shown that they have increased in intensity and duration in the past. And unfortunately, because of global warming, they’re just going to get worse. »
“These are fundamental changes and they are not reversible,” Harcourt said. “So we have to adapt quickly, and we don’t really think about it, especially right now because we’re all caught up in the pandemic.”
This story was published with permission from Mongabay.com.