Adriatic Sea changing with rise in new tropical and invasive species

Croatia’s Adriatic Sea

With the continued warming of the Adriatic Sea, new tropical and invasive species are making their home along the Croatian coast.

During a recent field expedition near Saplunara on the island of Mljet, researchers recorded and captured two such species – the marbled spinefoot and the devil firefish.

The marbled spinefoot, native to the Indian Ocean, Red Sea and Persian Gulf, was first spotted in the Adriatic in 2010. Since then, it has adapted well to the local environment.

“You can tell from the shape of its mouth that it has become suited to a plant-based diet. It feeds on brown macroalgae and even those growing on the leaves of Posidonia seagrass,” Dr Neven Iveša from the Faculty of Natural Sciences in Pula explained to HRT.

Despite its peaceful nature, the marbled spinefoot is having a significant impact. It competes with native herbivores and its overgrazing puts marine biodiversity at risk.

Though not highly venomous, its spines can cause discomfort.

“I accidentally stepped on one. The pain was not severe, but there was a brief stinging sensation. I applied heat to the wound and the discomfort quickly disappeared,” shared Iveša.

Devil Firefish

Alongside the marbled spinefoot, researchers are also increasingly encountering the devil firefish in the Adriatic.

This striking species is among the top hundred most invasive in the Mediterranean.

“It may look impressive, but it is a serious threat to our sea. It reproduces rapidly and reduces biodiversity,” warned Dr Milena Mičić, director of the Pula Aquarium.

Devil firefish (Pterois miles) (Photo credit: Alexander Vasenin/CC BY-SA 3.0)

The specimens found off Mljet are currently being kept in controlled conditions at the Pula Aquarium. However, experts caution that many more are likely present across the Adriatic. Their expanding numbers could severely destabilise the region’s marine ecosystems.

Dr Aljoša Duplić, director of the Institute for Environmental Protection and Nature, highlighted the dramatic changes now affecting both land and sea.

“The warming sea and the so-called tropicalisation of the Mediterranean are transforming habitats and encouraging the spread of new species that disrupt the existing balance,” he said.

The devil firefish and marbled spinefoot are examples of species that have migrated from the Red Sea through the Suez Canal into the Mediterranean, and are now entering the Adriatic.

“These tropical fish are surviving more easily as conditions change. Although the Adriatic is the most northern and coldest part of the Mediterranean, it is becoming increasingly suitable for them,” Duplić noted.

According to Duplić, devil firefish have already spread to the central Adriatic and are likely to reach the north soon.

“They reproduce quickly and pose a serious threat to native marine life. In Cyprus, for example, they have devastated local fish populations and endangered fisheries.”

He also pointed to worrying changes in sea temperature below the surface.

“The thermocline – the boundary between warm and cold water – is now dropping to depths of 40 metres. This alters the physical and chemical conditions of the entire water column, impacting all marine life,” he said.

“The sea as we know it will not be the same in the coming years.”

Rising temperatures, reduced rainfall, soil drying and higher evaporation rates are also having an increasing effect on land, especially forest ecosystems, transforming habitats and threatening numerous plant and animal species.

“The Ministry has funded research showing that seven of Croatia’s most common tree species will face significant shifts in their range. For instance, the pedunculate oak, currently widespread in the Pannonian region, could lose half of its natural area in the future,” Duplić warned.