Modeling the habitat suitability of Caulerpa sp. across the Galápagos Islands

Abstract

Globally, the number of invasive marine species has increased in recent years, posing a substantial risk both ecologically and economically. Throughout the Galápagos islands, two species of the green macroalgae Caulerpa, C. chemnitzia and C. racemosa, exhibit invasive tendencies, which may threaten native biodiversity. Characterized by fast growing species that reproduce asexually via fragmentation, the genus Caulerpa is known for successful invasion and establishment of populations outside of their natural range. We hypothesized that Caulerpa sp. are suitable for a broad geographic range in the Galápagos, with the potential to disperse beyond their current known ranges. Using R packages “terra” and “sdm”, we utilized an array of geospatial and presence/absence data to create a habitat suitability model for both species individually, and then ran a comparison of the two models. Findings indicate that the occurrence for both species is highly suitable in locations far beyond their current known range. For C. chemnitzia, the highest predictor for habitat suitability was sea surface temperature (AUC: 51.4%), and for C. racemosa was chlorophyll concentration (AUC: 44.5%). For both species, we also found that chlorophyll concentration was a high predictor of the model’s likelihood of occurrence (AUC: >35%). In addition, proximity to human population was found to be a strong predictor for C. racemosa suitability (AUC: >40%) which suggests anthropogenic activity is correlated with occurrence. Although model variable importance differed between species, results indicate that both species are highly suitable to occupy the same niche. This modeling approach serves as a cost-effective and efficient first step for prioritizing management efforts.