The non-indigenous tropical octocoral Carijoa established in the eastern Mediterranean Sea

Abstract

The Mediterranean Sea is warming at a rate exceeding the global average, facilitating the proliferation of thermophilic non-indigenous species, a process known as tropicalization. Despite over 1000 thermophilic marine species introductions, only two non-indigenous octocorals have been documented. This study presents photographic, taxonomic and genetic evidence that a third non-indigenous octocoral, the snowflake coral, Carijoa cf. riisei, has successfully colonized Limassol, Cyprus, a maritime hub in the eastern Mediterranean. Genetic analyses suggest that the snowflake coral is likely of Indo-Pacific origin, marking a northern expansion of its known biogeographic range. The snowflake coral is a common biofouler and produces planktonic larvae that can be transported through ballast water, which have contributed to its wide distribution in tropical and sub-tropical marine environments. Characterized by rapid growth, it can overgrow and smother local benthic invertebrates, significantly altering benthic community structures in invaded areas. Detected colonies survived and grew, and within a few years, dense colonies appeared, carpeting the hard substrata at adjacent sites. This recent proliferation raises concerns that a new invasion is underway. In the eastern Mediterranean, the snowflake coral has the potential to occupy the empty ecological space created by invasive herbivorous species and transform the seascape of vulnerable barren subtidal reefs to one where marine animal forests are the dominant feature. Our findings highlight the urgent need for ecological surveys to monitor the dynamics of this invasive octocoral and its potential role in driving ecological change, providing essential insights during the early stages of invasion.

Keywords: Invasive; Marine animal forests; Mediterranean; Snowflake coral.