Globally, endocrine-disrupting chemicals and warming waters could lead to smaller fish and reduce populations
Grace van Deelen for the Environmental Health News
For example, a cow might eat 100 pounds of grass, but only grows by 10 pounds. This rule sustains life on Earth and determines the pyramidal structure of the food chain.
However, new research shows that plastic pollution and warming oceans
could threaten to upend this rule, possibly creating unwelcome consequences for
marine species as well as the global food supply.
Researchers
on the study, published in January in the Proceedings of the Royal Society,
studied zebrafish in the lab and determined that warmer water and bisphenol-A
(BPA) — a chemical used in many plastics — together make fish metabolisms less
efficient at converting food into energy and body weight.
In
the study, zebrafish exposed to these two stressors needed more energy to grow
and reached a much smaller size at adulthood than their counterparts who had
not been exposed.
The global food web “depends on a certain rate of energy from one level being transferred to the next. If you disrupt that, you can disrupt whole ecosystems,” Frank Seebacher, an author on the study and a professor of biology at the University of Sydney, told EHN.
BPA,
one of the most abundantly used plastic additives in the world, affects fish —
and human — endocrine systems by disrupting the ability of hormones to signal
important body processes like growth and development. BPA contaminates fish via
plastic pollution in the ocean and through plastic materials used in
aquaculture (fish farming operations). While BPA is a prevalent
endocrine-disrupting chemical, others are present in
plastics, too, like phthalates and polyfluoroalkyl substances (PFAS). Such
chemicals have been shown to affect
fish growth on their own.
Research
shows that fish hormones and endocrine systems are also impacted by temperature: in
warmer water, fish metabolisms speed up, making the energetic cost of growth
much higher. Both warming and endocrine-disrupting chemicals impact fish growth
and development, making fish less efficient at converting their food into
biomass. When fish are exposed to both at once, said the researchers, the
problem is worse, and could lead to population-level impacts.
While
the study was done on zebrafish within the lab, changes in fish size have
already been observed in the wild, said Nicholas Wu, an author on the study and
a PhD student at Western Sydney University in Australia.
“This
is a growing problem,” he told EHN.
Population
level impacts
Less
efficient fish metabolisms spell trouble for marine ecosystems — especially
those animals at the top levels of the food chain, the researchers said.
Smaller fish at lower levels of the food chain mean that there’s less food to
go around, which could cause a decrease in populations of animals like sharks,
whales, or other large predators.
Additionally,
said Seebacher, when prey fish are found at lower numbers — and therefore are
spread further apart in the water — predators like sharks and whales must spend
more time and energy searching for food. That can be stressful for the animals
and threatens their populations as well.
Wu
also said that fish are not the only marine organisms for which this is a
problem; the metabolisms of some crustaceans, plankton, aquatic insects, and
marine mammals have also been shown in other studies to be sensitive to
endocrine-disrupting chemicals from plastic pollution. These chemicals disrupt
processes critical to the survival of these organisms, like body size,
development, and reproduction.
After
determining that warming water and plastic pollution disrupted fish growth,
researchers created maps to identify “problem areas,” or areas of the world
with many fisheries, high levels of plastic pollution, and faster-than-average
ocean warming.
They
determined that, under the RCP 8.5 warming scenario (one
commonly used climate model that assumes rising emissions continuing through
the 21st century), many fisheries in southeast Asia, Central America, and
equatorial Africa would be at high risk of changes in fish growth within the
next hundred years.
The
study comes as the latest Intergovernmental Panel on Climate
Change report warns that marine heat waves are already becoming
more common, longer, and more intense. The report further warns that climate
change will threaten marine life through
habitat loss, population decline, increased risks of extinctions, and the
rearrangement of marine food webs.
Impacts
on global food production
This
wouldn’t just impact marine fisheries: As a result of this growth effect, said
the researchers, aquaculturists who grow fish for human food production may
have to spend more money on feeding their fish for the same quantity of fish
harvested. Predatory fish like tuna, salmon, and marlin all require other fish
as food — if those other fish are smaller and less abundant, it becomes less
efficient and more expensive to grow predatory fish for human consumption.
“Successful
aquaculture operations rely on food and energy transfer efficiency,” Seebacher
said. “If that’s out, and it’s not commercially viable anymore, it produces
more pollution because it’s just inefficient.”
According
to the Food and Agriculture Organization
of the United Nations, fish provide, on average, 7% of the protein
in a person’s diet; for 3.3 billion people, however, fish provide more than 20%
of the protein they eat. Global demand for fish as food is expected to rise,
making it even more critical for those managing fisheries to attend to warming
and plastic pollution concerns.
Future
for fish
Seebacher
said he hopes that the findings of this research will inform management
strategies for fisheries, possibly leading to an adjustment in fish quotas to
help combat the potential decline in fish abundance. Aquaculturists, he said,
could benefit from replacing materials containing BPA that are used in their
aquaculture ponds, such as plastic tubing, liners, or containers.
The
problem of marine plastic pollution is only getting worse: according to one 2020
study, 11% of all plastic waste produced enters aquatic ecosystems, and global
waste management systems likely will not be able to keep up as the amount of
plastic produced each year continues to rise.
Some
areas of the world with extremely warm waters and high levels of pollution may
need to stop fishing for human consumption altogether, said Seebacher.
“The
results were really quite an eye opener,” he said. “This could have really
important implications.”
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