Concern about gelatinous plankton outbreaks has increased in the past decade, highlighting the dearth of information about the Ctenophore fauna in the Mediterranean Sea. The knowledge of the Ctenophore diversity of Greek seas is based on a handful of publications focusing on the distribution and population development of the invasive Ctenophores Beroe ovata and Mnemiopsis leidyi in the Aegean Sea, possibly due to the regional lack of taxonomic specialists.
In a paper published in the journal Acta Zoologica Bulgaria on 27 February 2020, Markos Digenis and Vasilis Gerovasileiou of the Institute of Marine Biology, Biotechnology and Aquaculture at the Hellenic Centre for Marine Research, report the first record of the lobate Ctenophore Leucothea multicornis from Greek waters, filling regional gaps in its known distributional range in the Mediterranean Sea.
The Comb Jelly was sighted on 29 July 2019, at depths of 1–2 m, at Dafnoudi Beach, Kefalonia Island (Eastern Ionian Sea), Greece. Samples were not collected but specimens were photographed. Taxonomic identification was based on detailed morphological descriptions.
The photographed specimen was about 18–20 cm in length and had a compressed body along the tentacular axis. Its color was translucent to milky white, while the pharynx and the inner portion of oral lobes were yellowish. The two large lobes were about the half of the total animal length and subdivided in two independent functional units. The lobes had numerous cylindrical papillae at their outer surface and subtentacular meridional canals forming complex loops at their interior. Subtentacular ctene rows were about half the size of substomodeal ctene rows. Both cteneal rows were nearly translucent, shimmering and arising near aboral extremity of the body. Subtentacular ctene rows extended to the base of lobes while substomodeal ctene rows to the extremity of lobes. Ratio of pharynx length to total length was about 2/3. Two opposing tentacle bulbs were present near mouth, at each side of flattened pharynx, and a long branching and extendable axial tentacle was associated with each bulb. Long auricles were arising at the oral end of subtentacular ctene rows between mouth and base of lobes.
Leucothea multicornis is widely distributed in tropical, subtropical and temperate waters, spanning across the Atlantic Ocean, Baltic, Mediterranean and Black seas, Western Indian and Southwestern Pacific Ocean. In the Mediterranean Sea, it has been reported from the western basin, the North Adriatic, Sicily and Malta, and recently reported from Israeli and Syrian waters. The lobate Ctenophore has yet to be reported from Turkish waters. Leucothea multicornis is the largest species of the lobate Ctenophores. According to Bella Galil, Shevy Bat-Sheva Rothman, Roy Gevili, and Tamara Shiganova, the sudden sighting of this large-sized and conspicuous species in the Eastern Mediterranean in 2014 is likely a new record for this marine area.
Therefore, Digenis and Gerovasileiou's finding from the Eastern Ionian Sea fills distribution gaps between the central and southeastern Mediterranean basins, being also the first record of this species from Greek waters. Further research on gelatinous zooplankton diversity of the Greek Seas and Eastern Mediterranean waters is required in order to investigate distribution patterns and monitor potential outbreak events. Citizen science initiatives could greatly assist towards filling relevant data gaps
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