Plastic pollution on coral reefs increases with depth and mostly comes
from fishing activities

Date:
July 12, 2023
Source:
California Academy of Sciences
Summary:
Researchers reveal the extent of plastic pollution on coral reefs,
finding that debris increases with depth, largely stems from
fishing activities, and is correlated with proximity to marine
protected areas.


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FULL STORY ==========================================================================
In a paper published today in Nature, researchers from the California
Academy of Sciences, University of Sa~o Paulo, University of Oxford,
University of Exeter, and other collaborators reveal the extent of
plastic pollution on coral reefs, finding that debris increases with
depth, largely stems from fishing activities, and is correlated with
proximity to marine protected areas.

Through underwater visual surveys spanning more than two dozen locations
across the Indian, Pacific, and Atlantic oceans, the researchers expose
the abundance, distribution, and drivers of plastic pollution at various depths, which in turn enables them to identify what conservation efforts
could be prioritized -- and where -- to protect our planet's vulnerable
coral reefs.

"Plastic pollution is one of the most pressing problems plaguing ocean ecosystems, and coral reefs are no exception," says Hudson Pinheiro, PhD,
the study's lead author, a biologist at the Center for Marine Biology
of the University of Sa~o Paulo, and an Academy research fellow. "From macroplastics that spread coral diseases to fishing lines that entangle
and damage the structural complexity of the reef, decreasing both fish abundance and diversity, pollution negatively impacts the entire coral
reef ecosystem." Surveying reefs from shallow to never-before-seen For
the study, the researchers conducted more than 1,200 visual surveys across
84 shallow and mesophotic reef ecosystems located in 14 countries. To
survey hard-to-reach mesophotic -- or 'twilight zone' -- coral reefs that
exist between 100 and 500 feet (30 and 150 meters) deep, researchers
relied on specialized diving gear that few other scientific dive teams
are trained to safely use.

According to the study, coral reefs appear to be more contaminated by
plastics and other human-derived debris than other marine ecosystems
that have been evaluated, but are much less polluted than shoreline
ecosystems like beaches and wetlands.

However, contrary to studies of near-shore environments, the researchers
found that the amount of plastic increased with depth -- peaking in the mesophotic zone -- and was mostly derived from fishing activities.

"It was surprising to find that debris increased with depth since
deeper reefs in general are farther from sources of plastic pollution,"
says Luiz Rocha, PhD, Academy curator of ichthyology and co-director of
the Academy's Hope for Reefs initiative, who was the senior author on
the study. "We are almost always the first humans to set eyes on these
deeper reefs, and yet we see human- produced trash on every dive. It
really puts the effect we have had on the planet into perspective."
Of the total debris, 88% was macroplastics larger than about two inches
(five centimeters). The researchers posit that the potential causes
of pollution reaching such depths include increased wave action and
turbulence near the surface dislodging trash and carrying it away,
recreational divers removing debris from more accessible shallow reefs,
and shallow corals with higher growth rates overgrowing the trash hiding
it from their surveys.

The lowest and highest densities of pollution Over the course of the
study, the researchers found human-derived debris in nearly all locations, including some of the planet's most remote and pristine coral reefs,
such as those adjacent to uninhabited islands in the central Pacific. The lowest densities of pollution -- around 580 items per square kilometer
-- were observed in locations such as the Marshall Islands. Comoros,
an island chain off the southeast coast of Africa, had the highest
density of pollution with nearly 84,500 items per square kilometer --
the equivalent of around 520 pieces of debris on one football field.

Troublingly, the researchers say that because these plastic-laden
deeper reefs are more difficult to study, they are rarely included
in conservation efforts, management targets, and discussions despite
harboring unique biodiversity that's often not found on shallow reefs.

"Our findings provide more evidence that the mesophotic is not a refuge
for shallow reef species in a changing climate as we once thought,"
says co-author Bart Shepherd, director of the Academy's Steinhart
Aquarium and co-director of Hope for Reefs. "These reefs face many
of the same pressures from human society as shallow reefs, and have a
unique and poorly-studied fauna. We need to protect deeper reefs and
make sure that they are included in the conservation conversation."
Fishing gear foremost source of pollution Although the researchers found
much consumer debris, such as water bottles and food wrappers, which
are often the main source of plastic pollution in other ecosystems,
nearly three-quarters of all plastic items documented on the surveyed
reefs were related to fishing like ropes, nets, and fishing lines.

"Fishing gear, which even as debris continues to catch marine life through
what we call ghost fishing, appears to contribute a large proportion
of the plastic seen on mesophotic reefs," says co-author Lucy Woodall,
PhD, principal scientist of Nekton and associate professor in marine conservation biology and policy at University of Exeter. "Unfortunately, fishing gear debris is often not reduced by general waste management interventions; therefore specific solutions related to the needs of
fishers should be considered, such as no- charge disposing of damaged
gear in ports or individually labelling gear to ensure fishers take responsibility for misplaced equipment." To uncover the drivers
of coral reef pollution, the researchers analyzed how the abundance
of human-derived debris correlated with a number of geographic and socioeconomic factors. In general, they found pollution on reefs increases
with depth and proximity to densely populated cities, local markets, and, counterintuitively, marine protected areas. Since most marine protected
areas allow some fishing within or near their borders and are typically
more productive than other locations due to their protected status, they
are often heavily frequented by fishers, according to the researchers.

"Our findings reveal some of the complex collective challenges we face
when dealing with plastic pollution," Pinheiro says. "As marine resources around the world dwindle, humans that rely on those resources are turning
to deeper habitats and those closer to marine protected areas where
fish remain abundant." Science-based solutions to fight reef pollution Ultimately, the researchers hope that by teasing out the major drivers
of pollution, as well as demonstrating that plastic pollution increases
with depth, conservation efforts can be redirected to better protect
and ensure a thriving future for Earth's coral reefs.

"The results of our global study shine a light on one of the many
threats that deep reefs face today," says study author and University
of Oxford marine biologist Paris Stefanoudis. "Because these ecosystems
are ecologically and biologically unique, much like their shallow-water cousins, they need to be conserved and explicitly considered in management plans." In particular, they stress the need to expand the depth of
marine protected areas to include mesophotic reefs, update international agreements on combating plastic pollution at their source -- such as
those discussed at the recent Intergovernmental Negotiating Committee
on Plastic Pollution -- to include fishing gear, and develop low-cost biodegradable alternatives to fishing gear that will not adversely impact
the well-being of coastal communities that rely on sustainable fishing
for their livelihoods.

"Despite the disturbing overall trend, there were some places where we
found relatively little debris, which shows us that there are effective strategies for preventing plastic pollution," Shepherd says. "If we act
fast and employ science-based solutions, there absolutely is hope for
coral reefs."
* RELATED_TOPICS
o Plants_&_Animals
# Fish # Fisheries # Marine_Biology
o Earth_&_Climate
# Ecology # Pollution # Coral_Reefs
o Science_&_Society
# Ocean_Policy # Environmental_Policies # Land_Management
* RELATED_TERMS
o Eutrophication o Environmental_effects_of_fishing o Coral_reef
o Artificial_reef o Dinoflagellate o Southeast_Asia_coral_reefs
o Water_pollution o Fishery

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========================================================================== Journal Reference:
1. Hudson T. Pinheiro, Chancey MacDonald, Robson G. Santos, Ramadhoine
Ali,
Ayesha Bobat, Benjamin J. Cresswell, Ronaldo Francini-Filho,
Rui Freitas, Gemma F. Galbraith, Peter Musembi, Tyler A. Phelps,
Juan P. Quimbayo, T.

E. Angela L. Quiros, Bart Shepherd, Paris V. Stefanoudis, Sheena
Talma, Joa~o B. Teixeira, Lucy C. Woodall, Luiz A. Rocha. Plastic
pollution on the world's coral reefs. Nature, 2023; 619 (7969):
311 DOI: 10.1038/ s41586-023-06113-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230712124626.htm

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