Sea turtles may be the answer to invasive pufferfish species

This alien species entered the Mediterranean through the Suez Canal and is now being recorded more and more frequently in Greek waters. The impacts of its presence are multifaceted.

It causes significant damage to fishing gear, affects the balance of marine ecosystems through competition with native species, while the tetradotoxin it contains makes its consumption dangerous for humans.

Amid this worrying picture, scientists are turning their attention to a potential natural ally: the loggerhead sea turtle.

The sea turtle is one of the few species that seem to be able to feed on the pufferfish, as it is immune to the tetradotoxin it contains.

“We know that turtles are immune to tetradotoxin and can feed on the pufferfish. They have very powerful jaws and we know this from their diet, which includes crabs, bivalves and other hard-shelled organisms,” explains Dr. Nikos Simantiris from MEDASSET (Mediterranean Association for the Salvation of Sea Turtles) to Greek media.

According to him, remains of the pufferfish have been found in the stomachs of washed up sea turtles, which confirms that the species is included in their diet.

The scientific data and what is still unknown

Despite the indications that the Caretta caretta may function as a natural predator of the loggerhead, scientists emphasize that further research is required before safe conclusions can be drawn about its role in limiting the population of the species.

Incidents from Turkey in 2019 and Egypt in 2020 are recorded in a scientific paper published in the journal Frontiers in Marine Science, examining the relationship between sea turtles and loggerhead turtles in the Mediterranean. However, to date, there is no direct visual recording showing a sea turtle actively hunting a live pufferfish or whether it feeds exclusively on dead fish.

The case of Zakynthos

One of the questions that scientists are examining is whether the large populations of kareta-kareta turtles in areas such as Zakynthos may affect the spread of the pufferfish. It is characteristic that both in the Bay of Laganas and in other marine areas of Zakynthos, reports of loggerhead turtles are minimal to non-existent.

According to Dr. Nikos Simantiris, the reports of fishermen from the Ionian Sea do not present the same picture as that recorded in Attica and Crete. “Although there is a small spread, there is not in the Ionian Sea, at least, the spread that we see in Attica and Crete. And given that the two largest sea turtle nesting areas in the Mediterranean are located there, it remains to be investigated whether the presence of such a large number of turtles can act as a deterrent to the spread of the species,” he says.

As he says, the most important nesting areas of the sea turtle in Greece are the Bay of Laganas in Zakynthos and the Gulf of Kyparissia, while significant populations are also hosted in Crete and in areas of the Aegean.

Decline in natural predators exacerbates the problem

The spread of the pufferfish is not only related to climate change, but also to the general degradation of the marine environment. Overfishing has led to the decline of large marine predators, such as swordfish, groupers and wrasses, weakening the natural control mechanisms of the populations of many species.

“The effort to protect the natural environment by all of us, in terms of anthropogenic impacts, is a significant help in addressing the phenomenon,” emphasizes Dr. Nikos Simantiris.

As he points out, climate change is a key factor in the spread of the hare's head, but overfishing and the degradation of marine ecosystems play an equally important role.

“The sea turtle is one of the most important biomarkers of the health of the marine environment. We need calmness, respect for the sea and protection of our ecosystems," he concludes.