The Mesocosm That Could
2000-Liter Tank ‘Mini Ecosystems’ Predict a Strange Oceanic Future
For one thing: Sharks might become... gentler?
Climate change is happening. Climate change is probably bad. But what does climate change actually do to ecosystems?
We really don't know—yet.
But researchers at Australia's University of Adelaide think they've figured out a way to predict the climate change future, by constructing 2,000 liter tanks replete with all the flora and fauna of the sea, and varying carbon dioxide levels.
This isn't necessarily new, per se. Previous versions of marine experiments like this used smaller tanks, about 20 to 50 liters in size. However, these experiments can be slow, and Ivan Nagelkerken, biological sciences professor at the University of Adelaide and leader of the project, said a comparatively enormous tank in instrumental for our understanding of future oceans.
“We have the natural cycling and acidity of water,” he told The Daily Beast. “You can’t mimic that if you test something in a little tank. We actually have this natural variability. We have sand that has been collected from the ocean with all these living organisms in sight—bacteria, little crabs, microorganisms, snails, seaweed, rocks with everything living in it.”
It took six months to set up the entire project, with 15 researchers working full time seven days a week to collect water, species and larvae from the sea, then filling the tank with sea creatures and water. Not only did these tanks have various kinds of life, they also simulated natural water currents and nutrients. In total, they had 12 tanks – three tanks were the control, three tanks had higher temperatures, three tanks had higher levels of carbon dioxide, and three tanks had both conditions combined.
Nagelkerken admits a giant tank of fish isn’t necessarily a realistic reflection of the ocean. “It’s still not nature but it’s a big step forward in terms of realism,” he stressed. “We were mostly interested in how fish will do under future climates.”
To simulate climate change, the researchers adjusted the temperature and carbon dioxide levels of the tanks and maintained these conditions for six months, matching current projections for climate change.
“You can’t manipulate carbon dioxide in the wild,” Sean Connell, ecology and environmental science professor at the University of Adelaide, said. “The best way to manipulate CO2 in the world in the future are these mesocosms.”
The team then measured the survival rate of the species and studied how they interact with each other. With mesocosms, scientists can easily replicate the tanks and regulate the temperature, pH levels and more. Also, they can study a more complete range of species.
One of the strangest, most frightening things the researchers noticed was how climate change affected sharks. Higher temperatures caused sharks to grow faster and have a higher demand for food. However, higher levels of carbon dioxide negatively impacted their sense of smell and ability to find food.
“There was a mismatch between sharks being hungrier but not able to find their food because of elevated CO2," Nagelkerken said. “You get a shrinking of the predator species simply because they can’t find enough food to keep up with metabolic demand.”
Sure, that might seem like an ideal future—one without a Jaws-like giant killer is certainly appealing. But the fact that sharks would be shrinking with an inhibited sense of smell gives us valuable insight into the trickle effects of smaller predators.
Still, mesocosms can have limitations since they aren’t nature. The team worked on a study this year by studying fish communities near volcanic vents, which naturally have high levels of carbon dioxide and high temperatures. The carbon dioxide acted as a nutrient for plants, and weedy algae took over these communities, benefitting “weedy” fish species. However, this leads to an overall loss in biodiversity. Predators should keep down the population explosion of these species, but without predators, they can multiply without limits.
“One thing that was really clear from our [volcanic] vent studies is the importance of predatory species is very high,” Nagelkerken said. “In natural conditions, predators keep down population explosions of weedy species. If you take away predators, weedy species can multiply without much limits.”
The team plans to continue studying climate change’s effects on marine ecosystems by using mesocosms and vents research. Now that they have measured the impacts, they plan to study the capacity of marine life to adapt to climate change, as well as positive fixes humans can engage in.
These effects directly affects humans as well. As fish stocks decrease in the future, humans may have to turn to other forms of nourishment, such as seaweed. The ocean’s ecosystems provide food, jobs and protection of coastlines. And humans can amplify these effects through overfishing.
“By catching too many predators and species, we’re also indirectly exasperating the effects of climate change by allowing weedy species to proliferate,” Nagelkerken said. “That’s important because we can’t change climate change on the short term because of the lag effect, but we can regulate fisheries through regulations. This is a way we can minimize climate change impacts.”