029 | The Strait of Messina as a biodiversity hotspot for cephalopods: evidence from 17 years of stranding events

Chiara Bacchiani¹, Giovanni Ammendolia², Teresa Romeo^3|4|5, Pietro Battaglia^1|5 | ¹Stazione Zoologica Anton Dohrn, Sicily Marine Centre, EMI Department, Messina, Italy; ²Independent researcher, Messina, Italy; ³Stazione Zoologica Anton Dohrn, Sicily Marine Centre, BEOM Department, Messina, Italy; ⁴Institute for Environmental Protection and Research, Messina, Italy; ⁵National Biodiversity Future Center, Palermo, Italy.

The phenomenon of stranding of deep-sea organisms is one of the most peculiar features of the Strait of Messina, resulting from the interaction between its specific geomorphology, hydrographic regime, astronomical (lunar cycle) and atmospheric (winds) influence. The observation of this phenomenon in the 19th century enabled scientists to ascertain that deep-sea fauna was also present in the Mediterranean Sea. Because of its richness, the Strait of Messina has been described as the paradise of zoologists and considered a biodiversity hotspot in the Mediterranean Sea. However, despite the importance of cephalopods in the trophic web of the marine ecosystem as a key species, they remain poorly investigated, especially for species of non-commercial interest. Given the difficulty of sampling, the collection of stranded specimens is a fundamental tool for assessing the biodiversity and ecological importance of this taxon in the marine ecosystem. The aim of the present study is to update information on the biodiversity and abundance of cephalopods, using the traditional collection of stranded specimens along the coast of the Strait of Messina as a sampling technique. Specimens (n= 168) collected from 2008 to 2024 were sampled in the morning, before and at sunrise. Overall 14 species belonging to several families (Enoploteuthidae, Brachioteuthidae, Ommastrephidae, Onychoteuthidae, Sepiolidae, Sepiidae, Tremoctopodidae, Octopodidae, Ocythoidae, Octopodidae, Argonautidae) were found stranded. Ommastrephidae was the most abundant family in terms of total number of individuals, mainly thanks to the species Illex coindetii. The sepiolid Heteroteuthis dispar was the most prevalent species recorded (n= 40). Stranding events have enabled the sampling of individuals belonging to rare or uncommon species such as Abralia veranyi, Brachioteuthis riisei, Argonauta argo and Ocythoe tuberculata as well as some interesting juvenile stages (e.g. Pteroctopus tetracirrhus). The lunar cycle, which influences the strength of currents (highest during full and new moon phases) and irradiance (higher in some lunar phases, such as the full moon) seems to affect the abundance of stranded cephalopods in the study area. The highest number of stranding events was recorded during the new moon phase, i.e. 38% of the total relative abundance of stranded cephalopods. Furthermore, the highest abundance of stranded specimens was recorded during the winter season. In conclusion, the study confirms the effectiveness of stranding as a non-invasive sampling method for monitoring cephalopods in Mediterranean waters.
This study was also part of the project “National Biodiversity Future Center - NBFC” (Project Code: CN_00000033), funded under the National Recovery and Resilience Plan (NRRP) by the Italian Ministry of University and Research and the European Union – NextGenerationEU.