Deep dive into Adriatic shows how industrial activity impacts on sea life

Up until the middle of the 20th century, the Adriatic Sea had a vibrant and healthy ecosystem before things suddenly crashed, according to new palaeontological research.

The Adriatic Sea is a body of water separating Italy and the Balkan states like Croatia, Bosnia-and Herzegovina and Albania. It is home to thousands of different marine species including many which are found nowhere else.

Analysis published in Proceedings of the Royal Society B shows that the trend in the Adriatic in the 1800s and early decades of the 1900s was positive for the sea’s marine life.

For example, carnivorous snails and their prey, clams, were on the increase.

Then their populations suddenly plummeted in the mid-20th century. In some cases, entire populations disappeared.

It was a boon, however, for one particular species of clam: the common corbulid clam (Varicorbula gibba).

This species can slow its metabolism when the going gets tough. It shows up in abundance in the fossil record whenever the environment becomes too challenging for other species to survive.

“This species became more abundant and grows much larger than it did previously because there are fewer predators and less competition from other species,” says first author Martin Zuschin, a palaeontology professor at the University of Vienna, Austria.

The finding adds to growing evidence that human activity has dangerously destabilised the Adriatic marine ecosystem.

“From our research in the northern Adriatic Sea, we can say that species composition in these environments is much simpler than it used to be,” Zuschin says. “In many places today, we’re lacking predators, grazers and organisms that live on top of the sediment, while other species, like deposit feeders and animals that live in the sediment, have become more abundant.”

The team’s research looked beyond declines in populations and numbers of species. They examined the interactions between species as well.

Most types of fossils don’t allow this kind of analysis. This is because bite marks and other physical damage which would indicate predator-prey interactions are seldom preserved in the fossil record.

But marine invertebrates – with their hard outer shells – are exceptions.

Predators, like snails, feast on shelled sea-floor creatures by boring holes in their shells to get at the soft innards. Other snails, worms and octopuses have evolved to grind and pulverise shells.

The researchers examined historical ecosystem trends by drilling cores in the northwest Adriatic along the mouth of the Po River in Italy, and the northeast Gulf of Trieste.

The scientists looked for bored shells to determine how much predator-prey interaction was taking place over time.

Core samples showed that there was an abundance of predator and prey up until the mid-19th century. Predators, prey and drill holes all spiked at around this time. This is from the early days of industrialisation in Italy.

“A moderate increase in nutrient input is good for the ecosystem,” he explains. But this soon overwhelmed the environment and fuelled the growth of algae. When the algae die, they sink to the seafloor and are broken down by bacteria, using up much of the sea’s oxygen.

“It simply became too much, and the whole system crashed,” Zuschin says.

Common corbulid clams may have thrived in these conditions where other species struggled. “They’re less vulnerable to lower oxygen levels than some of their competitors, and they can proliferate quickly,” says co-author Michal Kowalewski from the Florida Museum of Natural History, US.

Efforts are underway to reduce pollution coming through Italy’s rivers. The Po River sample even shows a small recent uptick in shell drill holes, suggesting some improvement.

But conservation, Zuschin says, will only get harder the longer it is put off.

“Environmental degradation is extremely expensive. You cannot even quantify it, because something that is gone that had a tremendous impact on the quality of life cannot be accounted for in terms of money.”