Assessing seahorses' distribution along the Italian coasts through citizen science and social media platforms

Seahorses are charismatic fish considered flagship species of the conservation measures. They are threatened by many factors, including habitat degradation/loss, bycatch, and direct exploitation, which have caused the decline of numerous populations worldwide. For this reason, all seahorse species were included in the IUCN Red List of Threatened Species, in which most of them (including the two European seahorses Hippocampus hippocampus and H. guttulatus) have been classified as 'Data Deficient' on a global level. The data on seahorses' distribution are, in many areas (including Italian coasts), scattered and patchy, thus preventing any correct classification of the two species' extinction risks. Seahorses are however difficult to survey in nature, due to their particularly cryptic traits. Therefore, we undertook a citizen science approach to estimate the abundance, distribution and demographic trends of H. hippocampus and H. guttulatus along the Italian coasts. One hundred and sixty-nine compiled surveys indicated a relatively wide distribution of the two species, with H. guttulatus most frequently observed; however, some Italian regions showed a sharply higher number of observations than others. Seahorses were mostly spotted in shallow waters, and despite some differences between the two species, artificial substrates were the most frequented habitats by both of them. According to the results of this study, citizen science is a powerful and cost-effective method for the detection and monitoring of seahorses that could be useful for future conservation plans.