Spirals in Time: The Secret Life and Curious Afterlife of Seashells (38 page)

It’s not easy to gauge how sensitive sea butterflies are to falling pH and rising carbon dioxide because they’re flighty in more ways than one: they’re especially tricky to keep alive in captivity. No one has yet worked out how to breed them, and they can’t be shipped between labs around the world, so the only way to study them is to go to where they are in the wild.

The search for sea butterflies lured Silke Lischka deep inside the Arctic Circle. Among various research trips, she spent a winter in almost perpetual darkness illuminated from time to time by the Northern Lights. She was in Kongsfjord in the Svalbard archipelago, halfway between Norway and the North Pole, where a purpose-built research station makes it possible for scientists to live and work quite comfortably in this remote outpost. While she was there, sea butterflies were not difficult to find. Swarms of them would drift into the fjord and hover in the water right in front of the research station, and some days she could have sat on the dock and scooped them up in a bucket, but usually she puttered out in a boat and gathered her samples from deep fjord waters.

These were
Limacina helicina
, a close relative of the spiralling sea butterflies we found in Gran Canaria, and one of only a handful of sea butterfly species that live in the Arctic. After hatching over the summer, the juveniles have to survive a long, dark, hungry winter, hanging on until the sun returns in the spring, when they mature into adults, mate and produce the next generation.

With extreme care, Silke carried the young sea butterflies back to her laboratory on the shores of the fjord and kept them in a range of temperatures and carbon dioxide levels, including those levels expected by century’s end. Then she measured their shells and examined them through a microscope for signs of damage.

At higher carbon dioxide levels, the transparent shells became more scuffed, perforated and scarred compared to those kept in more normal conditions; the high carbon dioxide sea butterflies were also slightly smaller, suggesting they weren’t growing so well. The sea butterflies she hit with the combination of higher carbon dioxide levels and higher temperatures often didn’t survive.

Repeating her experiments with empty shells, Silke showed that living sea butterflies can resist acidification to
some extent; they don’t get as badly damaged as empty, dead shells. But there’s no doubt that having to reinforce their dissolving homes, laying down more carbonate on the inside, puts a strain on the juveniles’ limited energy reserves. If this happened in the wild, the little sea butterflies would probably find it much harder to survive the winter.

Several other researchers have studied sea butterflies and uncovered similar gloomy forecasts of their demise. Clara Manno investigated sea butterflies in the far northern reaches of Norway. Her experiments showed not only that lower pH and higher carbon dioxide causes sea butterfly shells to lose weight, but she also revealed the confounding effect of freshwater. As sea ice and glaciers melt in a warmer world it’s expected that the salinity of surface seawaters will drop. When both pH and salinity were reduced, sea butterflies flicked their wings more slowly as they swam around Clara’s laboratory tanks, showing her that something was not right.

Like Silke,
Steeve Comeau
studied
Limacina helicina
in Svalbard, and found similar results, but he also ventured west to the Canadian Arctic, where he lived in a temporary research base perched out on the sea ice. Steeve collected his samples by lowering plankton nets through a hole in the ice. Back in the lab he found that the rate of calcification dropped by around 30 per cent in sea butterflies exposed to the carbon dioxide levels predicted by 2100.

In distinctly warmer waters, Steeve worked with larvae of a Mediterranean sea butterfly species. As he reduced pH, the larvae grew smaller, malformed shells. And he found that below pH 7.5, they didn’t grow shells at all – but they didn’t die. In the confines of the laboratory the naked sea butterflies seemed to get along just fine but there’s no knowing if they would survive in the wild. Nobody has yet found any naked sea butterflies in the oceans, but one research team has uncovered the next worrying part of the story: wild sea butterflies whose shells already seem to be dissolving.

In parts of the oceans, winds blowing across the sea surface cause deep, cold waters to upwell into the shallows. These deeper waters are naturally rich in carbon dioxide and undersaturated with carbonate ions.
Nina Bednaršek
has led studies of sea butterflies in two upwelling regions. The first, in 2008, was in the Scotia Sea that stretches between Tierra del Fuego, at the tip of South America, and the island of South Georgia in the Subantarctic. The second, in 2011, was along the western seaboard of North America, between Seattle and San Diego. At both sites, Nina found sea butterflies with signs of damage and shell decay similar to those seen in animals that have been through acidification experiments in labs. Her findings have been interpreted as a worrying sign of things to come.

Will it matter if sea butterflies start to disappear from the oceans? Will declines or shifts in their range send ripples of change through the rest of the open ocean ecosystems?

One way that a loss of sea butterflies would potentially matter is because they play a part in drawing carbon away from surface seas down into the deep and away from the atmosphere. They do this via carbon locked up in organic matter, mostly their faeces.

Clara Manno was the first to identify sea butterfly droppings. They are compact pellets, oval in shape, greenish brown and quite easy to spot once you know how. She calculated that a single sea butterfly produces around 19 droppings per day, and they sink rapidly through the water column. Sifting through sediment samples gathered from the Ross Sea off Antarctica, she calculated that almost a fifth of all the organic carbon sinking into the depths – the so-called organic carbon pump – consisted of pteropod poo. Add their abandoned mucous webs, plus their dead bodies that get dragged down by their shells, and it means sea butterflies could drive half of the organic carbon pump in some polar waters. It’s very difficult to predict exactly how things would change if sea butterflies were to begin abandoning acidifying
waters in the Arctic and Antarctic. Other planktonic species could conceivably move in and take their place in the ecosystem, but there is always the chance that they would be less effective at removing carbon from the atmosphere and pulling it into the deep sea. If the organic carbon pump were to weaken, it would add yet another twist to the tangle of problems caused by climate change.

Without sea butterflies, there would also be a lot of hungry sea angels out there, as they eat little besides sea butterflies. Seabirds and fish also eat sea butterflies (although not exclusively); they in turn are eaten by bigger fish, as well as whales and seals, making sea butterflies a potentially crucial link in ocean food webs, including ones in which people are involved; there’s a series of short hops from plankton to sea butterfly to salmon to dinner plate. If sea butterflies vanish or shift their ranges, it’s possible the animals that eat them will also have to move, or find something else to eat, or go hungry. Exactly how important sea butterflies are as food for other animals, and whether ecosystems would be disrupted without them, is not clear. Much more research is needed.

It’s true that sea butterflies can be extremely abundant and, when they are, other animals will often zero in and stuff themselves. Silke described to me a day during her time in Svalbard when a huge flock of sea butterflies drifted into the fjord; hundreds of kittiwakes and fulmars sat on the sea, merrily picking at the submerged feast. Other researchers have counted 10,000 sea butterflies in a single cubic metre of water, but such high densities only occur in patches that come and go.

A major challenge that lies ahead for ocean acidification research will be to move on from single-species studies. It’s all very well knowing how individual animals react when exposed to acidifying seawater, but what happens when hundreds and thousands of organisms are all interacting, eating each other and competing for space and food? There’s
one thing everyone agrees on when it comes to understanding the impacts of ocean acidification: it’s complicated. And most complicated of all will be predicting how entire ecosystems are going to respond. But researchers are finding ways.

How to probe an ecosystem

The departure lounge at Gran Canaria’s Las Palmas airport overlooks the runway, and beyond it the Atlantic stretches out to the horizon. For two months in the late summer of 2014, if passengers glanced up from their Starbucks coffee and gazed through the huge glass walls, they might have caught a glimpse of science in progress.

Nine orange structures nod gently in the sea. Each is a ring of floating pipes sticking up into the air and supporting the top end of a giant, tubular plastic bag; two metres (six feet) wide and 15 metres (50 feet) long, it hangs down into the water. Umbrellas keep the rain off, and rows of spikes stop birds from landing and pooping on them. Down on the seabed, piles of iron railway wheels are used as anchors to hold the equipment in place. These structures act as giant test tubes, designed to test the effects of ocean acidification, not just on single species but on the profusion of life that makes up an open ocean ecosystem.

There’s a bunch of clever things about these test tubes, which go by the name of KOSMOS, or the Kiel Off-Shore Mesocosms for future Ocean Simulation (mesocosm simply being a larger version of a microcosm, an encapsulated miniature world). For starters they are portable; they can be taken apart and shipped around the world, to repeat experiments in different sites, although this doesn’t come without its challenges. In Sweden, the KOSMOS tubes were frozen in by sea ice and the previous spring, in Gran Canaria, some were torn to shreds by huge waves whipped up in a storm.

The KOSMOS tubes also benefit from being very big. To do something like this on land would be laborious and far more expensive; it would involve building huge tanks and
pumping in seawater, causing who knows what confusion and damage to minute sea life in the process. Much better to take the test tubes to the ecosystem, rather than the other way round. The sides of the giant plastic bag are carefully lowered to enclose 55,000 litres of seawater and everything in it. Then the stage is set to manipulate conditions inside the tubes, in this case to pump in carbon dioxide at varying concentrations, to mimic the effects of ocean acidification.

Once that’s done, the contents of the tubes are sampled every day or two. Water samples are extracted from the water column in each tube, traps at the bottom catch sinking particles and plankton nets are dragged through. Sampling all nine tubes can take hours, out in the dazzling, subtropical sunshine, but the really hard work has still to begin.

Back in the PLOCAN labs, the samples are divided up between researchers who eagerly whisk them off and plug them into an array of complex analytical devices, incubators and microscopes. By the time I pay them a visit, the 40-strong KOSMOS team has already had a few weeks to smooth out the kinks in their protocols but, even so, I’m amazed at how seamlessly the whole project is running.

Everyone knows what they’re doing and the order in which things need to happen, as if they are part of their own well-functioning ecosystem. And what’s more, they are all still smiling despite the long hours, roasting air temperatures, questionable coffee dispensed by the machine in the corridor and, for many of them, the repetitive, mind-numbing tasks – like counting sea butterflies.

Silke Lischka’s job, along with her assistant Isabel, is to sort through all the debris caught in the sediment traps at the bottom of the mesocosm tubes and, as she and I had done, scour the plankton net samples. They do things a little more systematically, though; each of them has a counting chamber made from clear resin block with a long, narrow groove in it, the same width as the microscope’s field of view, into which they pour the samples. They work their
way along this elongated drop of water, counting sea butterflies as they go. Imagine an underground train driving slowly past while you stand on the platform counting all the people inside; you’re much less likely to miss anyone, or count twice, compared to standing by a crowded swimming pool and doing a head count. A tally of sea butterflies is kept using an old-fashioned, mechanical counter with typewriter keys that clack when they’re pressed and give a satisfying ding when they reach 100.

To get through all the samples takes hours, glued to a microscope, sometimes through long, sleepless nights. But I get a strong sense that everyone involved, especially Silke, knows why this is all worthwhile. They are contributing their part to a big, complex picture, probing the ecosystem from top to bottom, from the uptake and use of nutrients and the release of gases into the air, to viruses, phytoplankton and zooplankton. It’s too early to say how the experiment is going, how the sea butterflies and all the other parts of the ecosystem are responding to different carbon dioxide levels, but by the end of the project, and following a great deal of data-crunching, the team will take a step back and trace a labyrinth of invisible connections.

Similar studies have been carried out already in Arctic waters and off the coast of Scandinavia, but this is the first time the KOSMOS mesocosms have been deployed in open seas. Beyond the edge of continental shelves, these clear, blue, nutrient-poor waters are representative of what two-thirds of the oceans look like. Understanding what happens here is a major part of predicting how life across the planet will respond to ocean acidification.

Head of the KOSMOS project is Ulf Riebesell from GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany. I catch up with him after he has stayed up all night working on the latest stage of the experiment. The idea is to simulate the upwelling events that regularly take place when a steady current sweeping in from the north
stirs up eddies in the island’s wake, drawing deep water to the surface. The team used an enormous plastic bag to collect 80,000 litres of seawater, weighing 80 tonnes, from seven miles offshore and 650 metres down; the collecting bag took three hours to reach the surface, where it bobbed like a bloated whale. After they were set back a day by a broken water pump, the deep water was injected into the mesocosm tubes and all finally went according to plan. Now the team are on standby, waiting to see what effects unfold. They expect the nutrient-rich deep water will kick-start a phytoplankton bloom, and with it a feeding frenzy that will sweep through the rest of the ecosystem.