Australia barely had time to recover from record breaking fires at the start of 2020 before the Great Barrier Reef experienced its third mass coral bleaching event in the past five years. Only five of these have occurred since records began in the 1980s. High water temperatures and marine heatwaves, caused by climate change, are making coral bleaching an almost regular occurrence in some parts of the world.
Coral reefs are among the most vibrant ecosystems on the planet, but they are also very sensitive to stress. Meteorologists predict that 2020 is likely to be the hottest year on record, threatening yet more bleaching on reefs around the world. But it’s not just the coral itself that suffers.
Reef fishes exposed to high temperatures tend not to behave normally. Underwater noise and pollutants, such as agricultural pesticides, can have the same effect. Juvenile fish exposed to this kind of stress are less able to identify and avoid predators. But scientists aren’t sure exactly why this is.
In our new study, we found that a double whammy of higher water temperatures and pesticide exposure may be affecting the development of baby reef fish, with consequences for the entire ecosystem.
Metamorphosis in coral reef fish
Metamorphosis might bring to mind the transformation a caterpillar undergoes to become a butterfly, but it is also very common in coral reef fishes. After hatching from eggs, most reef fish develop as translucent larvae in the open ocean, before transforming into juvenile fish as they are recruited to their life on the reef.
This journey is a very important transition that is fraught with danger. Many predators like to eat reef fish while they’re in this small and vulnerable stage.
During metamorphosis, fish rapidly develop their eyes, noses and lateral line system, a special set of organs that allows them to detect changes in water pressure. Reef fish rely on these senses to spot and avoid predators.
Recent studies have shown that the process is regulated by hormones in coral reef fish. So if man-made pressures as diverse as increasing temperatures, underwater noise and pollution can cause juveniles to behave strangely and fail to avoid predators, perhaps it all has something to do with their hormones.
We decided to test this in a lab. We exposed the larvae of the surgeon convict fish to chemical hormones and hormone blockers and found that it directly influenced the development of their eyes, noses and lateral line systems. When fish received a hormone blocker, their sensory systems developed more slowly, they were less able to identify a predator by sight or smell and predators caught them more easily.
The lab tests showed that exposure to a hormone blocker can prevent fish from developing the necessary defences for life on a coral reef. So how might they be faring in the ocean, given that pesticides drain off the land into coastal waters, where these chemicals might disrupt hormones in fish?
In further experiments, we exposed fish to different temperatures and doses of a common agricultural pesticide called chlorpyrifos. Higher temperatures and high levels of the pesticide made fish worse at avoiding predators, but when given extra hormones, the fish recovered their abilities. This shows how climate change and pollution can affect how fish naturally regulate their development, and how important it is for them to be able to metamorphose in a healthy environment.
Hotter water and exposure to pesticides might seem like totally different things, but our results suggest they affect metamorphosis in a similar way. This is worrying, because most coral reef fish species metamorphose early in their lives, and if their environment changes too much, it might endanger entire coral reef communities.
Luckily, our results suggest that these negative effects are mostly felt at higher doses, but they are at the extreme end of what is already being detected on reefs. That means that we still have time, but our habits must change soon.
About the Authors
William Feeney, Postdoctoral Research Fellow in Evolutionary Ecology, Griffith University and Marc Besson, Postdoctoral Research Fellow in Marine Ecology, École pratique des hautes études (EPHE)
The Human Swarm: How Our Societies Arise, Thrive, and Fall
by Mark W. Moffett
If a chimpanzee ventures into the territory of a different group, it will almost certainly be killed. But a New Yorker can fly to Los Angeles--or Borneo--with very little fear. Psychologists have done little to explain this: for years, they have held that our biology puts a hard upper limit--about 150 people--on the size of our social groups. But human societies are in fact vastly larger. How do we manage--by and large--to get along with each other? In this paradigm-shattering book, biologist Mark W. Moffett draws on findings in psychology, sociology and anthropology to explain the social adaptations that bind societies. He explores how the tension between identity and anonymity defines how societies develop, function, and fail. Surpassing Guns, Germs, and Steel and Sapiens, The Human Swarm reveals how mankind created sprawling civilizations of unrivaled complexity--and what it will take to sustain them. Available On Amazon
Environment: The Science Behind the Stories
by Jay H. Withgott, Matthew Laposata
Environment: The Science behind the Stories is a best seller for the introductory environmental science course known for its student-friendly narrative style, its integration of real stories and case studies, and its presentation of the latest science and research. The 6th Edition features new opportunities to help students see connections between integrated case studies and the science in each chapter, and provides them with opportunities to apply the scientific process to environmental concerns. Available On Amazon
Feasible Planet: A guide to more sustainable living
by Ken Kroes
Are you concerned about the state of our planet and hope that governments and corporations will find a sustainable way for us to live? If you do not think about it too hard, that may work, but will it? Left on their own, with drivers of popularity and profits, I am not too convinced that it will. The missing part of this equation is you and me. Individuals who believe that corporations and governments can do better. Individuals who believe that through action, we can buy a bit more time to develop and implement solutions to our critical issues. Available On Amazon
From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.