Adapt, Change or Just Swim! Why Fish Will Not Face Climate Apocalypse

Vijay Jayaraj | September 25, 2018 | 2:56pm EDT
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LEVANTO, LIGURIA, ITALY - JULY 31 2017: a flock of sarpa salpa is seen during a dive inside the marine reserve of Cinque Terre (UNESCO Heritage) on May 17, 2017.

It is said that modern man-made climate change impacts ocean life, more specifically the life of marine fishes. It is said that some species could become extinct or vulnerable in the near future.

However, are these claims true, and what does the available empirical evidence suggest?

During my three years as a graduate student at the University of British Columbia’s Changing Oceans Research Institute (CORU), after earning my M.Sc. in environmental sciences, I had the opportunity to study the adaptability of marine fishes to changes in ocean temperatures.

The CORU, in academic circles, is known to be one of world’s leading research centers for determining the impact of climate change on ocean life. Its research outputs carry high importance and usually incorporate into the UN Intergovernmental Panel on Climate Change’s (IPCC) assessment reports.

In 2017, a research study originating from CORU claimed that increasingly warm waters, from man-made climate change, will result in smaller fish.

The study’s primary results revolved around the hypothesis that fish are limited by gill size in their ability to intake oxygen from warm waters that are being depleted of oxygen due to on-going climate change.

The authors of the above study make an implicit assumption that man-made climate change in recent decades impacts the life of marine fishes adversely. Here are a number of problems with the conclusions of their study.

1.    Open Borders—Vertically and Horizontally

Fishes are not restricted by barriers. With no barriers restricting their movement, they can easily move to cooler waters. While this is applicable to both their horizontal movement and their vertical movement, the focus is more on their horizontal movement to cooler waters on either side of the equator (the water is increasingly colder as one moves away from the equator either northward or southward).

Strangely, the authors of the same above-mentioned study have done another study that documents this ability of fish to avoid any potential burn-outs by moving to cooler waters.

2.    Adaptation—Genotypic Evolution and Phenotypic Plasticity

While many well-wishers of marine life focus on their supposed inability to survive in warm waters, they seldom address the natural adaptive mechanisms that are built into these fishes. We should not forget that these fishes have already gone through genetic variation since they first appeared in Earth’s waters that has enabled them to have adequate biological characteristics (including gill size) not just to survive, but to thrive. Moreover, they also have the ability to adapt to changing local environmental conditions, an ability more commonly known as phenotypic plasticity.

Both generational genetic adaptations and local phenotypic adaptations are commonly observed in the fishes that currently populate our oceans and will help them avoid burn-out from any potential warming.

3.    Been there, Felt that, and Still Alive

Current temperature levels are very similar to those that the oceans experienced during the Roman Warm Period (1st century A.D.) and the Medieval Warm Period (11th century A.D.). This means that the very same fishes have experienced and survived through temperatures that were as warm as today’s levels, and there is no reason to believe that the current temperatures will make them shrink or disappear.

The Little Ice Age (17th century A.D.) marked a sharp decline in global temperatures. The fishes survived this period, too, and managed to adapt to temperature changes that relentlessly increased from the 18th century to the present.

4.    The world is not just about the gill size!

By limiting the determination of survival of fishes solely to their gill size, proponents of marine apocalypse have failed to reflect the overall biological structure of the marine life system. Phytoplankton, which the fishes depend on for food, have increased dramatically with the increase in temperature since the Little Ice Age. This has resulted in a healthier and thriving marine biome. It is important to note that phytoplankton are the base of several aquatic food webs, providing food for a wide range of marine life including fishes. Moreover, phytoplankton growth is resilient to even the sharpest changes in temperature and known to survive major changes in earth’s environmental condition. So even if the phytoplankton mass goes down, there is no reason to believe that they will be severely impacted.

These are just four reasons out of many why fishes won’t face a climate apocalypse. The dangers of climate change to marine life have been exaggerated in our mainstream media, and academic research centers should undertake a more holistic approach to study the response of marine fishes to changing temperatures.

The resilience of our marine life is high, and we are yet to fully understand how these life forms manage to do this. It is fair to conclude that research on the impact of climate change on marine life is still in its infancy. Regardless, there is currently no danger to ocean life from warming temperatures.

The biggest threat to marine life is from over-fishing, illegal fishing, and ocean pollution. Environmental factors such as ocean acidity and temperature changes have largely remained stable and have seldom impacted the life of marine organisms in the past 200 years.

Vijay Jayaraj (M.Sc., Environmental Science, University of East Anglia, England), Research Associate for Developing Countries for the Cornwall Alliance for the Stewardship of Creation, lives in Chennai, India.


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