It wasn’t just birds that were affected. The Blob was also implicated in a cetacean ‘Unusual Mortality Event’ (UME) that saw 46 whale carcasses – mostly fin and humpback whales – stranded on the coastlines of British Columbia and Alaska. Another UME was declared at the same time for fur seals and California sea lions, with malnourished, starving and dead animals washing up along the entire California coast from January 2015 onwards. Those that could be saved were taken to rehabilitation centres where malnourished pups were provided with nutrition and hydration so that they could be re-released when conditions improved. Fisheries were also affected, and a harmful algal bloom led to toxins contaminating shellfish along the coasts of Washington, Oregon and California. All told, scientists writing in the journal Nature Climate Change concluded, ‘it is possible that the northeast Pacific warm anomaly of 2014–15 is the most ecologically and economically significant marine heatwave on record.’
Other marine areas have been hit by their own versions of ‘The Blob’. On the Atlantic coast of South America a 2017 marine heatwave brought the hottest-ever recorded sea temperatures over a wide area, causing mass mortalities of fish and a toxic algal bloom just a few miles offshore from Uruguay’s capital city. In 2010 to 2011 a marine heatwave off the coast of Western Australia damaged huge areas of ecologically important seagrass meadow and led to a long-term decline in the population of bottlenose dolphins. Marine heatwaves ‘have already become longer-lasting and more frequent, extensive and intense in the past few decades’, a 2018 Nature Climate Change paper concluded, reporting data showing that marine heatwave days doubled between 1982 and 2016. Another 2018 paper, published in Nature Communications, found that ‘from 1925 to 2016, global average marine heatwave frequency and duration increased by 34% and 17%, respectively, resulting in a 54% increase in annual marine heatwave days globally.’ The explanation was straightforward: a rise in average ocean temperatures. In other words, the culprit was global warming.
A more recent paper, published in March 2019, concluded that marine heatwave days have increased by 50% in recent decades as compared with the first half of the 20th century. Lead author Dan Smale compared the impact of hotter oceans on marine ecosystems to wildfires on land. ‘You have heatwave-induced wildfires that take out huge areas of forest, but this is happening underwater as well,’ he told the Guardian. ‘You see the kelp and seagrasses dying in front of you. Within weeks or months they are just gone, along hundreds of kilometres of coastline.’
Bleaching corals
The oceanic ecosystems most endangered by marine heatwaves are tropical coral reefs, which are experiencing devastating bleaching episodes as they are swept by ever-hotter waters. In 2016 and 2017 Australia’s Great Barrier Reef suffered back-to-back mass bleaching events that virtually wiped out large areas of this 2,300-km-long ecosystem. Terry Hughes, a world expert on corals, surveyed 900 sections of the reef during and immediately after the 2016 bleaching event from the air. ‘I showed the results of aerial surveys on bleaching on the Great Barrier Reef to my students,’ he tweeted on 19 April 2016. ‘And then we wept.’
Hughes and colleagues subsequently published a paper in Nature that detailed an ‘unprecedented ecological collapse, extending southwards from Papua New Guinea for up to 1,000 km’. In the worst-hit northern 700-km section of the reef, where heat exposure was most extreme, 50% of coral cover on reef crests was lost within eight months. With the staghorn and tabular corals suffering a ‘catastrophic die-off’, the three-dimensionality and ecological functioning of nearly a third of the 3,863 reefs that together comprise the world’s largest coral reef system was transformed. Mass bleaching was easy to spot from the air, with large sections of reef converted into areas of deathly white visible through the clear water. The southern section of the reef was only saved from the same fate by pure luck, when cooling wind, cloud-cover and rain from a passing tropical storm rescued it from the rising temperatures that were devastating corals elsewhere.
Any lingering optimism about the longer-term fate of the reefs must surely be misplaced. Coral bleaching was virtually unknown in the world’s oceans before the mid-1980s. This means that corals have evolved little protection to rising heat that might help them adapt or speed ecological recovery. For example, a bleaching event in 1998 killed large areas of staghorn coral surrounding Orpheus Island off the Queensland coast. Now, 18 years later, photographs of the same site show it still covered with muddy debris and exhibiting no sign of recovery. Even when some ecological rebound does take place, bleaching events are now arriving too frequently for the reefs to recover anything like their previous diversity before the next event strikes. The latest studies now show that marine heatwaves are becoming sufficiently intense to skip the bleaching process altogether and kill coral organisms directly. The exposed reefs, left vacant by the dead coral polyps, are draped with a layer of algae within a few days, and later begin to dissolve.
The 2016 worldwide bleaching event, as well as devastating the Great Barrier Reef, also had ‘catastrophic impacts’ – according to scientists later reporting in Nature – in the Red Sea, central Indian Ocean and across the Pacific Ocean and the Caribbean. In some areas corals were bleached right down to what should be much cooler areas 90 metres below the sea surface. In the Arabian Gulf, where corals were assumed to be reasonably accustomed to higher sea temperatures, reefs spread over 350 kilometres of the southern basin of the Gulf were bathed in lethally high temperatures for over a fortnight. Mass bleaching ensued, and two-thirds of corals were killed outright. By the next year, just 7.5% of the original coral cover was left. Reef scientists were particularly shocked at the scale of this loss because the Gulf corals were supposed to be more resistant to bleaching as they were used to higher temperatures. Yet they still died.
The coral die-off has transformed once thriving reefs into ‘more degraded systems, with just a few tough species remaining,’ scientists report. No wonder so many coral experts are in despair. A recent feature in Nature reported that many marine biologists who work on the Great Barrier Reef are experiencing ‘ecological grief’ at witnessing the real-time breakdown of one of the world’s most beautiful and valuable ecosystems, something that they have loved and studied throughout their careers. Researchers also feel the weight of knowing what has been lost, and the reality that their children will never enjoy the pristine and thriving reefs that they themselves remember.
Meanwhile, the extinction clock is ticking. The final demise of the reefs may come sooner than even many scientists expect, not just because of increased bleaching or thermal stress, but because corals are increasingly failing to reproduce at all. Researchers have found that juvenile corals, which need a solid anchor point on the seafloor to start growing, cannot establish new colonies on a bed of algae and mud-covered rubble. Although new coral colonies are moving poleward in a desperate effort to stay within thermally tolerable waters, studies have found a more than 80% reduction in their worldwide reproductive success since the 1970s. Recent work on the Great Barrier Reef found a 90% collapse in the reproductive capacity of the corals, though perhaps this is hardly surprising since most of the sexually mature adults over large areas are already dead.
Coral reproduction used to be one of the great wonders of the world. Despite being unable to communicate directly, corals are somehow able to spawn over hundreds of kilometres simultaneously on a single night, this miraculous synchrony coordinated through a complex combination of environmental cues and the phases of the moon. Eggs and sperm can only survive in the water for a matter of hours, so successful fertilisation depends critically on coral colonies all releasing their sexual material at the same time. However research conducted in the Red Sea, published in Science in September 2019, suggests that this system, which evolved over millions of years, is beginning to break down in the face of record-breaking sea temperatures. Corals are losing their spawning ‘synchrony’ – in other words they are going out of tune, with colonies spawning in an irregular way over different nights or even failing to spawn at all. This synchrony breakdown drastically reduces the probability of successful fertilisation, which in turn reduces the numbers of young corals and may eventually ‘drive aging populations to extinction’.
I don’t know whether the researchers wept when they saw what was happening to coral spawning in the Red Sea. But it would be strange not to suffer ‘ecological grief’ at the sight of billions of coral eggs dispersing uselessly into the warming ocean, and at the thought that the prospects of the next generation of these spectacular corals has been stolen. This is a future stolen ultimately not just from tropical corals, Cassin’s auklets or golden toads. It is also stolen from our own children, who will never know the amazing and spectacular world that we enjoyed when we were young. Already, at one degree, our globe is becoming impoverished and reduced. We might all weep for what we have done.
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