Taking a detour: invasion of an octocoral into the Tropical Eastern Pacific

Abstract

The tropical snowflake octocoral Carijoa riisei, which is thought to be native to the Indo-Pacific biogeographical region, has been increasingly reported from the Colombian Tropical Eastern Pacific (TEP) over the past two decades. Massive mortalities of native octocorals, particularly in Pacifigorgia spp. and Muricea spp., were observed due to C. riisei overgrowth. However., the area of origin of TEP C. riisei remains unknown and its potential invasive status has not been addressed yet. We evaluated geographical scenarios for the colonization of the Colombian TEP by conducting phylogeographical analyses based on nuclear and mitochondrial sequences of 306 individual specimens from across the species’ (native/non-native) range and applying hypothesis-specific operational criteria. Additionally., we assessed whether C. riisei has to be considered an invasive species based on the previously proposed ‘unified framework for biological invasions’. Our results showed relatively high genetic differentiation between Colombian TEP populations, on the one side, and Indo-Pacific and Hawaiian populations, on the other side. In contrast, we could not identify genetic differentiation and significant isolation by distance (IBD) between Colombian TEP and Tropical Atlantic populations. C. riisei might have been introduced from the Atlantic into the Colombian TEP, possibly via the Panama Canal. Based on the criteria of the ‘unified framework for biological invasions’, we also conclude that this octocoral constitutes an invasive species. Our study may serve as a basis for establishing strategies to protect native species from one of the very few invasive coral species worldwide.