Fish Are Losing Their Sense of Smell

By Marlene Cimons

There have been numerous wake-up calls about the effects of climate change on marine life. As ocean waters heat up, they are bleaching corals. Growing levels of carbon dioxide are acidifying seawater, which is degrading the shells and skeletons of sea organisms. The rising temperatures are prompting fish to migrate to colder waters, even causing them to shrink.

Now climate change is starting to affect their sense of smell, a phenomenon that will worsen in the coming years if global warming continues unabated, according to new research. A sense of smell is indispensable to fish. They use it to find food, detect imminent danger and elude predators, to find safe environments and spawning areas, even to recognize one another.

To lose it could threaten their very survival. If this happens, it also would mean big trouble for the fishing industry, tourism and, most importantly, global nutrition, since many of the world’s people — including its poorest — depend on fish for food.

Fishermen in Vietnam. PHOTO: Pexels

“Future levels of carbon dioxide can have large negative effects on the sense of smell of fish, which can affect fish population numbers and entire ecosystems,” said Cosima Porteus, a researcher at the University of Exeter and author of the study, which appears in the journal Nature Climate Change.

“This can be prevented, but we must reduce carbon emissions now before it’s too late.”

Carbon dioxide combines with seawater to produce carbonic acid, which makes the water more acidic. Since the Industrial Revolution, oceanic CO2 has risen by 43 percent and is projected to be two and a half times current levels by the end of this century, according to the scientists.

Experts believe that about half of anthropogenic carbon dioxide — that is, emissions produced by human activities, such as the burning of fossils fuels — has over time ended up in the oceans, lowering the pH of seawater, and making it more acidic.

Porteus — collaborating with scientists from the Centre of Marine Sciences in Faro, Portugal and the Centre for Environment, Fisheries and Aquaculture Science in the UK — compared the behavior of juvenile sea bass at carbon dioxide levels typical of today’s ocean conditions with those predicted for the end of the century.

The sea bass used in the study. PHOTO: Cosima Porteus/Nature Climate Change

They found that sea bass exposed to the more acidic conditions swam less and were less likely to react when encountering the smell of a predator, offered to them in the form of very dilute monkfish bile. Also, they were more likely to “freeze,” a sign of anxiety, she said.

“I found the longer they were in high CO2, the worse they fared,” she said.
The scientists also measured the ability of the fish to detect certain odors in different levels of acidity by recording their nervous system activity. “I recorded the olfactory — smell — nerve response by measuring the electrical activity of the nerve to these different odorants in the water that flowed over the nose of the fish in both normal and high CO2 seawater,” Porteus said.

“The odorants tested were those that would be involved in finding food — amino acids — and in recognizing fish of the same or other species, including bile acids, bile, intestinal fluid, etc., at different concentrations, and at levels they would encounter in the wild,” she added.

The researchers found that seawater acidified with levels of carbon dioxide that are expected by the end of the century — if global warming continues — reduced the sense of smell of sea bass by half, compared with today’s levels.

“Their ability to detect and respond to some odors associated with food and threatening situations was more strongly affected than for other odors,” Porteus said. “We think this is explained by acidified water affecting how odorant molecules bind to olfactory receptors in the fish’s nose, reducing how well they can distinguish these important stimuli.”

They did not compare the impact of today’s ocean acidity levels with those of pre-industrial times, although they plan further research to do so. “It is possible that sea bass are already being affected by a rise in oceanic pH,” she said.

Fresh catch at the fish market. PHOTO: Pixabay

The researchers also studied the impact of high levels of CO2 and acidity on genes expressed in the nose and brain of sea bass and found them altered — but not in a good way. Rather than adjust, things deteriorated, Porteus said.

“The gene expression experiment was conducted to see if these fish were able to compensate for their loss of sense of smell over a short period of time, not generations,” she explained. “Animals have some ability to respond to a stressful condition by making more proteins or different proteins that work better under different conditions.”

Researchers can determine this by looking at what genes change or are different between animals exposed to different conditions, normal and high CO2, for example, according to Porteus.

“One way to smell something better is to have more receptors detecting these smells in order to increase the chance that particular smell will be detected, and therefore increase the expression of these receptors,” she said. “Another way is [for them] to make a slightly different receptor that works better under lower pH. However, we did not find any evidence this was the case.”

Instead, they found the fish were making fewer such receptors, making it more difficult for them to detect smells, she said.

“There was a decrease in ‘active’ genes, indicating that these cells were less excitable, therefore responding even less to smells in the environment,” she said. “This means that these fish had a reduced sense of smell and instead of compensating for this problem, the changes in their cells were making the problem worse. This matched our observations of their behavior.”

Sea bass. PHOTO: Pixabay

The team chose to study European sea bass because they are an economically important species, both for food consumption and for sport fishing, Porteus said.

Nevertheless, “we think the ability to smell odors is similar in most, if not all, fish species, so what we have found for sea bass will almost certainly apply to all fish species, and maybe invertebrates too, such as crabs, lobsters etc.,” she said. “So all the commercially important species are likely to be affected in a similar way, such as salmon, cod, plaice, turbot, haddock etc.”

This is important because 20 percent of the protein consumed by 3 billion people comes from seafood, and about 50 percent of this comes from fish caught from the wild, according to Porteus. “Therefore, increases in carbon dioxide in the ocean have the potential to affect all fish species, including those that many people rely on for food and livelihood,” she said.

Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.

Going Back in Time in Raja Ampat

Sailing S/V Mir through remote Raja Ampat has been like traveling back in time to a wilder, less-peopled world.

Underwater in Raja Ampat. Photo by Gaie Alling, Biosphere Foundation

I spend a lot of time imagining what this planet was like even just a few centuries ago, before people began altering Earth’s living systems on a global scale. Human beings have been leaving their mark on the lands they inhabit for millennia, even causing extinctions, but it wasn’t until recently that the long reach of mankind has begun to affect nearly every corner of this globe, including the oceans, which were once thought too vast to deplete.

When I hike near my home in coastal California I often imagine scenes of what it used to look like there: scenes of stumbling upon an entire pride of mountain lions bent over an elk kill, their golden faces wet with blood. All around the cats are bald-headed California condors, shaggy in their oversized coats of black feathers, hopping and grunting and looking comically-huge as they wait with impatient eyes for a chance at the spoils. I imagine the Central Valley when it was still a vast wetland, and how the temperature must have dropped when the sky went black with migrating birds in the spring and fall. I imagine the lowland grizzlies that could get fat all year round without ever needing to hibernate in those temperate climes, lolling on their enormous woolly backs on a beach after a feast of elephant seal. Those bears must have been mythically huge.

By 1924, grizzly bears were completely eradicated from California. It’s disturbing how short a time it took people to tame this world, leaving only vapors of its original wildness. I seem to always be on the lookout for that untouched place, that glimpse into what this planet was like before our species watered it all down, and I’ve perhaps come closer than ever before to finding traces of that old world this past month as we’ve sailed Mir across remote Raja Ampat.

After leaving our friends in Mansuar, the crew aboard Mir headed towards the island of Wayag in northwestern-most Raja Ampat. Along the way we crossed the equator, and in the matter of a millimeter we sailed from summertime right on into winter.

Wayag is stunning and otherworldly — a vast and meandering mass of uplifted karst limestone islands surrounding countless bays and brilliant turquoise lagoons. The islands are green with vegetation, some are long and peninsular and steep, while many are small and stand alone, their grey bases all pocked and jagged and eroding into the shapes of mushrooms where they meet the ever-gnawing seas. Some are pointed in the likeness of arrowheads, and many are circular and rounded, like gumdrops.

Wayag Island. Photo by Nadia Low (and her drone), Biosphere Foundation

On one of our first mornings in Wayag I paddled for hours through a vast shallow lagoon that was full of young black-tipped reef sharks, presumably enjoying a respite from the big, bad ocean beyond. The lagoon was also speckled with hawksbill sea turtles who would watch with calm curiosity from below as my paddleboard approached them, probably thinking it nothing but an average bit of jetsam. Once I was right above them they would rise to the surface with the utmost mellowness and poke their pointed faces above the waterline where they would momentarily gawk at me in bewilderment before darting away in a frenzied panic.

“Holy Tortuga, there’s an enormous sunburned monkey on that thing!”

Paddleboarding in Wayag. Photo by Sam Keck Scott, Biosphere Foundation

One evening, I paddled through the narrow opening of another lagoon, this one deep and emerald and surrounded on all sides by thick jungle and the eerie booms of spice imperial pigeons. It felt like I was paddling through a freshwater lake instead of a salty lagoon until I’d get close enough to the shore to see a blue-spotted stingray zip past me, or a coral bommie haloed in reef fish. Here, a glimpse into that untouched world I’m always searching for.

Most mornings we would randomly choose one of the nearby mushroom islands to scuba dive around, and we were never let down by our picks. The reefs were pristine and fanatic with sea life. We saw corals that looked like enormous bouquets of oversized roses, and others like thick, bony bramble patches. Some were huge brains with labyrinthine channels, and others opalescent fingers. There were vast areas of reef that resembled a thousand small fists raised proudly in protest, and coral bommies that formed underwater mesas and plateaus and buttes, and others that appeared nebulous as they waved and swished with sea fans and soft corals. All of them were engulfed in a profusion of fish life of every color and size and shape, some so wildly patterned it seemed only a nonconforming second-grader could have painted them.

Titan triggerfish. Photo by Gaie Alling, Biosphere Foundation

I experienced many operatic moments where I would be skimming above a reef with the sunlight feathering down all around me and tornadoes of fish above me and baby sharks darting through curtains of massive barracuda, and I would feel something that is becoming more and more elusive to me: hope. Hope that this world may actually be resilient enough to weather us humans.

Happy reef. Photo by Sam Keck Scott, Biosphere FoundationA wobbegong shark camouflaged against the seafloor and surrounded by reef fish. Wobbegongs are ambush predators, meaning they stay still and hidden until prey swims close enough for them to strike. Photo by Gaie Alling, Biosphere FoundationA many-spotted sweetlips resting in a coral. Photo by Sam Keck Scott, Biosphere FoundationHawksbill sea turtle and Captain Laser. Photo by Gaie Alling, Biosphere Foundation

We had a cookout on a small beach near our anchorage on one of our last evenings in Wayag. In the wee hours of the night I was lying on my back in the sand looking up at the stars; it looked as if the Milky Way had touched down to fill the entire channel of Wayag Bay with thick, woven starlight, so close it seemed I could reach up and swirl it with my fingertips. I paddled back to the ship that night beneath that frenzy of stars and with each paddle stroke the water around me burst with bioluminescence — that starlight of the sea — and I felt like I was rowing right through the cosmos. I finally understood how the Polynesians had been able to read the night sky like a map; a map that was not only above them, but that they were navigating straight into. Once again, even if only fleetingly, I had found another piece of that old world.

That’s not to say that this part of Indonesia is actually untouched — far from it. At times we’ve seen what look like flowing rivers of trash caught in narrow current lines that flow past our ship uninterrupted for hours: plastic bottles, flip-flops, bags, food wrappers, even an entire television. And though the coral is faring much better here than it is in many other parts of the tropical world, we’ve still witnessed plenty of anchor damage, signs of dynamite fishing, and corals that look unwell and stressed from disease, excessive nutrients in the water, and bleaching. Anyone who came here even thirty years ago would probably tell you it’s trashed now; three-hundred years ago and Wayag Bay must have been boiling up to its banks with sharks and rays and turtles. But even now, even in the year 2018, it is still sacredly beautiful here, and the ecology remains intact enough to act as a nursery to repopulate our depleted seas with corals and fish and sharks and turtles, if we could only just leave it alone, if we could only just let it be the blazing technicolor wilderness that it’s always been without mussing it all up.

Raining fish in Raja Ampat. Photo by Sam Keck Scott, Biosphere Foundation

After leaving Wayag we slowly made our way back to the town of Waisai on the island of Waigeo, where we are currently resupplying for our voyage back to Bali. Along the way the beauty continued: late one night in the Bougainville Strait we watched bottlenose dolphins riding our bow; their torpedo-like bodies completely encapsulated in electric blue bioluminescence. And one morning at sunrise, manta rays breached off our stern through the apricot-lit water as we weighed anchor in the Dampier Strait.

But it seems time has had its way with us — as it’s wont to do — and after all the planning, the researching, the imagining, and the effort, we’re already getting set to leave Raja Ampat. Luckily for us, we have a month to get to Bali, which means we can take our time and keep exploring along the way, as well as stopping at Moyo Island for a few days to visit the Biosphere Foundation’s “Friends of Moyo” project.

To anyone who has been keeping up with this blog and is curious, yes my back is better, and thank you for your concern — what a relief to have gotten well so I could go back in time in Raja Ampat and get a taste of a world that once was, and a world that I would like to see return.

Blue-spotted stingray hiding beside a heart-shaped Acropora coral. Photo by Sam Keck Scott, Biosphere Foundation

Please keep following along on the rest of our adventures here, and to learn more about the Biosphere Foundation, visit our website at: https://biospherefoundation.org/

Originally posted 2018-03-04 10:20:57.

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