Biodiversity and Conservation

Abstract

Understanding the patterns and drivers of the spread of exotic species is necessary for limiting their distributions and minimizing their impacts on biodiversity. Species that are spread unintentionally versus intentionally present distinct management challenges that must be addressed with unique solutions. We assessed the spread and impact of exotic gecko species in the greater Caribbean region—a taxa and region predicted to be conducive to a high rate of unintentionally spread exotic species. From the literature, we compiled a database of exotic gecko introductions to the greater Caribbean region, recording the year of introduction, introduction pathway, establishment success, habitat use, and ecological impacts. Exotic gecko species introductions have increased exponentially over time and geckos from multiple biogeographic realms are now present in the greater Caribbean region. Species from distant realms were largely introduced intentionally to Florida via the pet trade, whereas Caribbean endemics were mostly introduced to other Caribbean islands through unintentional or unknown pathways. Regardless of the introduction pathway, most introductions resulted in established populations, usually in anthropogenic habitat. Furthermore, the exotics, Hemidactylus mabouia and H. frenatus, appear to be on the ‘winning’ end of most species interactions, including those with other exotics. Overall, our results show exotic geckos are spreading both unintentionally and intentionally with a strong potential to displace native gecko species and impact ecosystems as generalist predators. As eradication success is usually low, future conservation eforts should focus on elucidating ecological impacts and preventing new introductions through pathway-specifc trade policy, fnancial incentives, and education.

Abstract

The effect of recreational SCUBA diving on coral reefs is likely secondary to many of the commonly cited stressors that threaten the long-term survival of coral reefs, such as rising temperatures. However, recreational SCUBA diving has had documented effects on various benthic organisms. Most research on the effect of SCUBA divers has focused on broken and abraded benthic organisms or the rate at which divers contact the benthos. We tested for differences in the structural complexity and benthic assemblage between pairs of heavily and lightly trafficked dive sites in Bonaire, a popular Carribbean diving destination. There was roughly 10 % less structural complexity in areas of heavy traffic. This is alarming given that the structural complexity of shallow reefs in Bonaire is substantially lower than in the 1970s. Different functional groups of benthic organisms were affected differentially by diving traffic. For instance, massive corals such as Orbicella annularis were 31 % less abundant at heavy than light diver traffic areas, while gorgonians and sponges had similar abundances at heavy and light diver traffic areas. Our results match those of previous studies on the resistance and resilience of tropical benthic reef organisms to physical disturbances that suggest that stony corals are more prone to physical damage than gorgonians and sponges. We provide a number of possible management strategies that could reduce the effects of recreational SCUBA divers on Bonaire and elsewhere, including education/intervention by dive guides and concentration of diving traffic away from areas of stony coral abundance.