Unexpected coexistence of two species of garden eels (Heteroconger klausewitzi and Heteroconger pellegrini) in a colony at Gorgona Island, Colombia.

Garden eels are known to form large single-species colonies on the sandy bottom of tropical nearshore areas throughout the world's oceans. Passing divers are met by areas full of almost identical snake-like creatures, with their upper bodies protruding out of their burrows, in which they retract quickly as intruders approach. However, during a 15-day expedition to the Gorgona Island, in the Pacific Ocean of Colombia, it was discovered that the garden eels might not be so identical after all in that area. Between August and September 2019, individuals of both Heteroconger klausewitzi and Heteroconger pellegrini were observed co-existing in the same colony, which was previously believed to be exclusively comprised of the species H. klausewitzi. Photo and video evidence of this co-existence was obtained, and three individuals of H. pellegrini were collected. A ratio of 95.9% of H. pellegrini and 4.1% of H. klausewitzi was obtained from counting individuals appearing in the obtained videos. Heteroconger klausewitzi was found at depths greater than 12 m, while H. pellegrini was present from 5 to 12 m depth. This appears to be the first report of the existence of multi-species colonies in garden eels, suggesting it is a new case of inter-species colony association in fishes, which opens a new window for ecological and social behavior studies. In addition to multi-species coexistence, this work also is the first report of H. pellegrini in South America (i.e., Colombia), extending its distribution range southward by approximately 550 km. [ABSTRACT FROM AUTHOR]