Habitat and body size effects on the isotopic niche space of invasive lionfish and endangered Nassau grouper

Abstract

Abstract. Species invasions are a significant threat to global biodiversity and ecosystem function, and yet our knowledge of consequences for native species remains poor. The problem is exacerbated in highly speciose ecosystems like coral reefs. The invasion of the wider Caribbean by predatory lionfish (Pterois spp.) is one of the most successful marine colonizations ever documented, and its impact is anticipated to be substantial on native species. However, despite the ecological and commercial importance of iconic Nassau grouper (Epinephelus striatus), the impacts of the invasion on this IUCN Red-Listed species remain unexamined. Using data gathered from two critical habitats in the Bahamas, we investigate isotopic niche space overlap between lionfish, Nassau grouper and putative prey species. Despite their relatively small body size, we find that lionfish occupy the highest isotopic niche position on patch reefs, occupying much of the same space as the native apex predator. Contrary to expectation, lionfish trophic level (d 15 N) does not increase with body size, contrasting with confamilials in their native range. However, we find that tissue carbon (d 13 C) changes systematically with body size on deep forereef habitats, representing a lengthspecific shift in food resources, with smaller individuals partitioning resources from larger individuals in this habitat but not on shallow patch reefs. We conclude that, despite the difference in body size, lionfish are capable of directly competing for food resources with Nassau grouper, and that impacts on guilds such as planktivores and invertivores may vary systematically by habitat. Our study contributes to the growing body of research aimed at understanding how a species that is relatively rare in its native range achieved the most successful fish invasion ever documented.

Trophic niche size and overlap decreases with increasing ecosystem productivity

“…However, the few that have generally confirmed the theoretical relationship defined by MacArthur and Pianka (1966). For example, the size and degree to which the isotopic niches of lionfish Pterois volitans and Nassau grouper Epinephelus striatus overlap is related to the size of habitat these generalist consumers are sampled from; large, continuous reefs had grouper and lionfish with largely separated, small niches, while shallow, unproductive patch reefs held fish that had large, overlapping niches (O'Farrell et al 2014). The alignment of our results with established theory and the few natural examples in the literature underscores the validity of this novel method and its potential usefulness in the empirical demonstration of theoretical ecological relationships.…”

Individual isotopic specializations predict subsequent inter‐individual variation in movement in a freshwater fish

“…, O'Farrell et al. ). Together, these findings suggest that the combination of behavioral and dietary specialization we observed, were not likely to be a function of ontogeny or body size related heterogeneity, within the size ranges of fish tested herein.…”

The lionfish Pterois sp. invasion: Has the worst‐case scenario come to pass?

“…Nevertheless, to our knowledge, there is no indication of territoriality by lionfish or overt interference competition with native fish in the introduced range. Instead, by virtue of their high predation rates (Côté & Maljković, 2010;Green et al, 2011;Albins, 2013) and extensive overlap of prey use with native predatory fishes (Layman & Allgeier, 2012;O'Farrell et al, 2014;Curtis et al, 2017), lionfish have the potential to deplete resources shared by native mesopredators and perhaps exercise more subtle interference competition via fear effects. But do they?…”