Evidence on the presence of the butterflyfish Chaetodon hoefleri Steindachner, 1881 (Perciformes: Chaetodontidae) in the Mediterranean Sea

The four-banded butterflyfish Chaetodon hoefleri Steindachner, 1881, is a species native to the Tropical Eastern Atlantic. In this contribution, we report the occurrence of an individual in the Western Mediterranean Sea (WMED), off the coast of Al Hoceïma (Morocco). The record was based on a high-resolution photo uploaded and shared on the citizen science Facebook group, TunSea. Hereby we report an obvious signalization and we briefly describe it. The main pathways of penetration of the butterflyfish into the Mediterranean are also discussed. The role and the effectiveness of the citizen science are revealed again as an early warning system for non-indigenous species introduced into the Mediterranean Sea.