Habitat suitability and area of occupancy defined for rare New World sea snake

Abstract

Hydrophis platurus xanthos is a marine reptile endemic to the inner basin of Golfo Dulce, Costa Rica, and one of only two sea snake taxa found in the New World. In this study we assessed several marine conditions that describe its habitat, and we define its geographical distribution range. We used 423 occurrence records of H. p. xanthos collected during multiple studies to model habitat suitability in Maxent considering water depth and 12 interpolated hydrographic variables: Beaufort wind force, sea surface temperature, and averages of temperature, salinity, dissolved oxygen, turbidity, and pH at 0.5 and 10 m based on probe readings collected in 2020 and 2021 at 68 sampling locations. We used area under the curve (AUC) to evaluate our Maxent models and the cloglog minimum training presence threshold to render our suitable habitat maps. The most influential environmental predictor was depth, but occurrences were also affected by hydrographic conditions. Indeed, a model excluding depth consistently identified only areas in and around the inner basin area as suitable, suggesting the sea snakes are not only restricted by depth but likely have adapted to water conditions that differ from those farther to the south and outside the gulf in the broader Pacific Ocean. Anthropogenic and climate-induced changes may already be impacting the marine environment of this single, isolated population. Our study offers the first quantitative evaluation of habitat suitability for H. p. xanthos and we estimate its extent of occurrence (282 km2) and current area of occupancy (260 km2) to inform conservation assessments and guide protection measures.