Acid Trap Endangering the Entire Marine Food Chain

March 26, 2018

Earth’s oceans are beginning to warm and turn acidic, endangering plankton and the entire marine food chain.

At the Woods Hole Oceanographic Institution on Cape Cod, Massachusetts, snowdrifts piled up outside shuttered T-shirt shops, and wind and whitecaps lashed vessels tethered to empty piers in the harbour. The flood of sun-tanned tourists and research students that descends on this place in summer was still months away. The only visitor was a winter storm that hung over the coast, making travel in and out of the cedar-shingled town impossible. In a research building downtown, at the end of a dimly lit hallway, Peter Wiebe sat with a stack of yellowed composition notebooks, reliving a lifetime spent on the ocean. Wiebe, a grizzled scientist emeritus, is transcribing his research cruise logs, which go back to 1962. His handwritten notes archive a half-century of twilit cruises in the Antarctic and languorous equatorial days surrounded by marine life.

‘It’s quite clear to me things are changing,’ he told me, after I asked him to think back on his decades on the ocean. ‘As a graduate student on one cruise, my logs talk about a hammerhead and two whitetips following the ship the whole time. On other cruises, we would fish for mahimahi and tuna, and occasionally catch a shark. Now we hardly ever see any big fish or sharks at all.’

Indeed, in oceanography, the big story over the past half century – the span of Wiebe’s career – has been the wholesale removal of the seas’ top predators through overfishing. But the story of the oceans for the coming century may be a revolution that starts from the bottom of the food chain, not the top.

‘I won’t be around to see it,’ Wiebe told me. ‘I wish I were.’

Plankton (taken from the Greek word for wanderer) are the plants, animals and microbes that are unable to overcome the influence of ocean currents, either because they’re too small, like bacteria, or because, as in the case of the indifferent jellyfish, they can’t be bothered. Wiebe’s speciality is zooplankton, the kaleidoscopic, translucent animal world in miniature, much of which feeds on even smaller photosynthetic life called phytoplankton. To make the jump from photosynthesis to fish, birds and whales, you have to go through zooplankton first.

Wiebe is part of a body of researchers worldwide working feverishly to find out how these grazers will be affected by an increasingly unfamiliar ocean, an ocean that absorbs 300,000 Hiroshimas of excess heat every day, and whose surface waters have already become 30 per cent more acidic since the dawn of the Industrial Revolution.

‘When I first started, the idea that you could actually change the pH of the ocean just wasn’t there – no one expected us to be able to do it,’ Wiebe told me. ‘Certainly, no one expected us to be able to do it at the pace we’re doing it, at a pace that far surpasses anything natural that has ever happened.’

Nowhere on Earth are these changes more apparent than at the poles. Every year, in the Southern Ocean, swirling blue-green eddies of phytoplankton pulse with the seasons. These hurricanes of life are vast enough to be visible from space, but invisible in a handful of water. Pteropods – tiny translucent snails that long ago left the ocean bottom for a life of fluttering through the sea on winged feet – can mow huge patches of these carbon-rich blooms in a day. Along with other zooplankton such as krill, they drive the so-called biological carbon pump.

When zooplankton such as pteropods feast on the bloom, some of it sinks to the deep in a marine snowdrift of poop, half-eaten meals and other webs of protein that gather organic bits and pieces as they fall to the ocean floor. With 300 million tons of carbon shuttled to the deep every year in this manner, it’s a blizzard that can accumulate over time. The White Cliffs of Dover are one such edifice of plankton. And pteropods themselves, which sink like stones when they’re not beating their gossamer wings, can pile up on the sea floor by the billions, forming carbon-rich oozes.

However, just as important as their role in shuttling carbon to the deep is their place in the marine foodweb. Pteropods feed whales, fish and seabirds alike. They are the crucial second step in the transformative process that coverts sunlight into whales.

If they are esoteric to Westerners, pteropods are a bona fide cultural phenomenon elsewhere. In Japan, shell-less pteropods known as sea angels that prey exclusively on sea butterflies (their shelled relatives) frequently wash ashore, borne on currents from the arctic. The Japanese are obsessed with these visitors. Pteropods have inspired two Pokemon characters, a pteropod Hello Kitty, and tiny pteropod figurines that Sapporo occasionally packages along with its beer.

The roiling drama of the planktonic world is a theatre of ambush predators, hermaphrodites and mucus-hurling cannibals

Researchers are also doing their best to glamorise pteropods, in an attempt to garner public attention and funding. They are trying to rebrand pteropods and their ilk as ‘charismatic microfauna’ and with good reason. The roiling drama of the planktonic world is wilder than any savannah or jungle. It is a theatre of ambush predators, hermaphrodites and mucus-hurling cannibals.

If the film March of the Penguins (2005) was marketed on the premise that traditional family values prevail in the animal kingdom, the life cycle of pteropods would seem to represent a rebuttal. Male pteropods mate with each other, and then switch genders while holding onto the sperm, which they use to fertilise themselves. To feed, they cast out giant webs of slime that occasionally ensnare their fellow pteropods, whose innards they promptly suck out. The tiny snails have a softer side as well, with some species tenderly rearing their babies inside their shells. When they’re frightened, they nervously retract their wings, and plummet to the depths. It’s a sound strategy in a world where predators attack from all directions in space, with all manner of sci-fi appendages, including bioluminescent snares.

When they aren’t being hunted, much of the pteropods’ lives are spent dancing in the water column in a lilting flutter. The animals are hypnotising to watch, but it isn’t their ghostly beauty that attracts researchers. It is their alarming vulnerability. In the icy waters of the Antarctic, they are already beginning to dissolve.

In 2008, during an Antarctic research cruise north of the old whaling redoubt of South Georgia Island, the marine biologist Nina Bednaršek began to pull up net tows of the tiny marine snails. As expected, the nets were lined with pteropods, but something was off: their delicate calcium carbonate shells were pitted with holes.

Carbon dioxide reacts with seawater to make carbonic acid. Deep seawater naturally has more carbon dioxide, and less oxygen, simply because it is old. It has been breathed for centuries by everything alive in the ocean without remixing with oxygen from the surface. These frigid depths are a natural source of acidic water that wells up from time to time. When the water is acidic enough it dissolves calcium carbonate of the sort that makes up pteropod shells.

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