The seascape ecology of invasion: A test with indo-Pacific lionfish on Caribbean coral reefs

Background/Question/Methods

There is growing recognition that many invasions occur across heterogeneous environments rendered patchy through either natural or anthropogenic processes. However, little research has addressed how invasion dynamics are affected by spatial landscape patterns, which can alternatively help or hinder spread by influencing dispersal, adaptive potential, species interactions, and resource availability. The objective of this study was to examine the relevance of these concepts in the marine environment, where invasions represent a rapidly growing threat to biodiversity. The invasion of Indo-Pacific lionfish (Pterois volitans and P. miles) on coral reefs throughout the Caribbean provides a convenient model system to investigate of the importance of seascape structure for invasion dynamics. The significant ecological impacts of this invasive predator provide an added impetus to understand both dispersal patterns and underpinning processes to optimize the use of limited resources for management. To investigate the effect of landscape structure on movement, lionfish were externally tagged at a patchy (n=37 lionfish) and continuous site (n=44) off the island of Eleuthera, in The Bahamas. Movement was measured by GPS during resighting surveys over 8 weeks, and landscape metrics were measured directly along transects and remotely from satellite imagery.

Results/Conclusions

As predicted by theory, we observed greater dispersal by lionfish in patchy environments, where individuals had to move larger distances in order to find suitable habitat. Tagged fish were resighted at least once less often on patchy (61%) than on continuous (71%) sites, and subsequent migratory turnover was more rapid in the former environment. Most lionfish in patchy environments maintained long-term residency within small activity ranges (x̅=25 m²) encompassing the resident patch, with infrequent long-range excursions (300–800 m) across open habitat to neighbouring patches. In contrast, lionfish in continuous environments undertook frequent small-scale movements within larger ranges (x̅=552 m²). Body size affected dispersal differently depending on seascape structure: body length and trip leg length covaried negatively in continuous environments but positively in patchy environments, potentially due to the importance of body size for dispersal ability. These results support a significant role for seascape structure in invasion dynamics, and suggest that infrequent but large-scale displacements could accelerate invasive range expansion in patchy environments.  Moreover, our findings can help managers to set appropriate removal frequencies based on expected rates of inbound migration for a given environment, and by informing the selection of removal sites that minimize the probability of inbound migration following clearing.