Why sea urchins are disappearing

Sea urchins are at risk of disappearing, even in Italian waters. Since 2003, the crisis has only worsened, and by 2025, in some areas of the peninsula, such as Puglia and Sicily, the decline is expected to be between 80 and 90 percent, with fewer than 0,2 sea urchins per square meter. But what are the causes leading to the disappearance of these marine invertebrates, so precious to the ecosystem?

The accelerating sea urchin crisis is undoubtedly linked to the climate crisis, which in turn leads to increased harmful emissions and ocean acidification. Everything is connected: Rising temperatures indicate an increase in CO2 emissions, which forms carbonic acid, decreasing the pH of the sea. Acidification makes it harder for the sea urchin to form shells and skeletons, without which they cannot survive. And it becomes difficult for the invertebrate to grow and survive in the larval stage.

Apart from the specific disease Pollution, which kills sea urchins, leads to a buildup of heavy metals (mercury and lead) and pesticide residues in the vital organisms of sea urchins. Furthermore, various pollutants reduce fertility and increase malformations: fewer sea urchins are born and they struggle to survive.

When fertilizers and wastewater enter the sea, bacteria and algae proliferate, and oxygen levels drop below the safe levels needed for survival. Finally, the microplastics: They affect sea urchins just like fish, are ingested accidentally, but block digestion and poison.

The stringent local restrictions put in place to curb sea urchin fishing (in some areas it is only allowed for a certain period of the year, in others it is completely banned) have failed to stop illegal fishermen who continue to harvest even the smallest sea urchins, which is absolutely prohibited. The minimum size for which fishing is permitted is 5 centimetres, including spines. Alongside professional fishermen, tourists are also failing to comply with restrictions on sea urchin catches, thus contributing to the worsening of the species' crisis.

Uno scientific study of 2025 published on Scientific Reports (a magazine of the group nature), edited by the Universities of Salento, Palermo, Pisa and Malta, and by the Nbfc Research Centre and the Anton Dhorn Zoological Station of Naples, concludes its investigation by speaking of .