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Human activities are ravaging Adriatic mollusk communities

The current environmental crisis associated with human activities is more damaging to some wildlife than tens of thousands of years of major climate changes, according to a new study led by the Florida Museum of Natural History. The experts report that mollusk communities, which were incredibly resilient to major climatic shifts during the last ice age, are now withering under the strain of human activities. 

The results of the study show that mollusk communities were extremely resilient to past changes in temperature, salinity and sea level, but are struggling to endure the burden of human development and overfishing in the region. 

“It is sobering to consider that about 120,000 years of major climate change did not affect these ecosystems nearly as much as the human-induced changes of the last few centuries,” said study senior author Michał Kowalewski.

This is not the first time that scientists have recognized a human driven shift in modern Adriatic ecosystems.

“There are multiple human-driven stressors on these ecosystems, such as changes in land use that increase sedimentation rates,” said study co-author Rafał Nawrot. “This has occurred as far back as the Roman Empire, when increased agriculture led to higher rates of erosion.”

While prior civilizations along the Italian peninsula have left a notable signature on Adriatic ecosystems, most of the changes have occurred within the last century, explained Nawrot. These changes include pollution, as well as fertilizer runoff that has depleted oxygen in marine and freshwater environments. 

In particular, commercial fishing is possibly the biggest threat to Adriatic mollusks. “The Adriatic Sea is the most heavily trawled area in the world,” said Nawrot.

“By looking at the fossil record, you can reconstruct a range of natural variability,” said study lead author Professor Daniele Scarponi of the University of Bologna. “If the present-day community falls outside that range, it’s probably because of us.”

For the investigation, the researchers analyzed more than 70,000 marine mollusk fossils dating back to the Late Pleistocene. 

At the peak of the last ice age, sea levels dropped by about 400 feet and the northern portion of the Adriatic nearly vanished altogether. The shores retreated over 150 miles south toward the Mediterranean.

“It would have been possible to walk from modern-day Italy to Croatia,” said Professor Scarponi. “The entire northern part of the basin was exposed and transformed into an immense lowland plain.”

The experts focused their study on fossils which date back to before, during and after the last ice age to identify changes to mollusk communities. The results show that as oceans receded, mollusks that live in colder regions flourished in the Adriatic, while those that need warmer water did not. 

Despite some severe population declines, however, the researchers note that very few species disappeared altogether. 

“The main difference between mollusk communities through the glacial/interglacial cycles isn’t extinction or the appearance of new species, but rather changes in relative abundance,” said Nawrot.

At the end of the ice age, the Adriatic Sea bounced back – along with the abundance of mollusks. 

“Our fossil analyses show that communities of mollusk species along northern Adriatic coasts essentially re-assembled into a nearly identical image of themselves when the sea returned,” said Kowalewski.

“Temperatures during the last interglacial were actually a few degrees higher than they are at present, and yet we see the same associations of mollusks,” said Professor Scarponi. “That means near-shore mollusk communities will likely be resilient to a slight increase in temperature going forward.”

On the other hand, Nawrot warns that a warmer world brings with it a unique set of compounding problems. “Many stressors, like anoxia and the effects of invasive species will only intensify with warming, even if higher temperatures alone wouldn’t be a huge deal.”

The study was published in the journal Global Change Biology.

By Chrissy Sexton, Staff Writer

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