4.1 Environmental variables
Our study confirms the importance of environmental variables in shaping the distribution of sea snakes, which is consistent with previous studies (Bessesen et al. 2023; Udyawer et al. 2014). Environmental variables play a crucial role in determining the habitat suitability and area of occupancy of marine species, including sea snakes, and prioritizing search efforts based on habitat suitability models can help locate previously unknown populations of endangered marine reptiles (Udyawer et al. 2020). This aligns with our findings and emphasizes the importance of our research in generating crucial information that could guide future conservation and management strategies for protecting a highly vulnerable and ecologically important group, which is sea snakes.
Our findings are consistent with a meta-analysis on the importance of variables used in MaxEnt species distribution models, which found that the most important factors in determining the distribution of marine organisms were temperature, bathymetry, and precipitation (Bradie and Leung 2017). Additionally, our study highlights the importance of nutrient availability in shaping the distribution of marine species. Those environmental variables were not important in the meta-analysis. The study by Bosch et al. (2018) found that temperature, bathymetry, and distance to shore were the most important predictors for marine species distribution, while salinity and nutrients had less influence. Although our study’s results on the importance of salinity and nutrients in determining sea snakes’ distribution appear to conflict with previous analysis, it is worth noting that our study specifically focused on sea snakes, which may have different environmental preferences than other marine species. Our study’s results on the importance of phosphates, salinity, and temperature in determining the habitat suitability and area of occupancy of sea snakes are consistent with the findings of Bessesen et al. (2023) on H. platurus and Udyawer et al. (2014) on sea snakes in the Great Barrier Reef Marine Park.
The combination of climate and nutrient variables are known to have implications for the morphology, diving behavior, feeding habits of sea snakes and also coral reefs health (Brischoux et al. 2012; Gherghel et al. 2018; Heatwole et al. 2012; Sherratt et al. 2018; Veron 2000, 2008). Temperature, along with salinity, plays a crucial role in the physiology of sea snakes, affecting their metabolic rates, oxygen uptake, and blood chemistry (Heatwole et al. 2012; Udyawer et al. 2016). Studies have also demonstrated that metabolic thermal sensitivity optimizes sea krait amphibious physiology, enabling them to tolerate fluctuations in temperature (Dabruzzi et al. 2012; Heatwole et al. 2012). Furthermore, trophic specialization drives morphological evolution in sea snakes, while the dependence of dive behaviors and metabolism on temperature has also been observed (Dabruzzi et al. 2012; Sherratt et al. 2018; Udyawer et al. 2016). However, plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming, which may lead to mosaic patterns of thermal stress with implications for climate change (Gunderson and Stillman 2015; Helmuth et al. 2006). Phosphates play a significant role in the distribution of sea snakes as they are essential for the growth and development of the coral reefs where sea snakes are commonly found (Veron 2000). Although the importance of nitrogen and silicates in the distribution of sea snakes is less clear, they are likely to play a role in the availability of prey species that sea snakes feed on (Gherghel et al. 2018). Nitrogen is an essential nutrient for many marine organisms, and its availability can influence the abundance and distribution of prey species (Brischoux et al. 2012). Silicates are important in the growth of diatoms, which are a primary food source for many marine organisms, including some species of sea snakes (Sherratt et al. 2018).
The sea snakes’ distribution may have influenced their diet and feeding behavior, as species that occur in areas with higher nutrient availability may have evolved to specialize on prey that require higher energy requirements, such as fish, while species occurring in areas with lower nutrient availability may have evolved to specialize on prey that require less energy, such as crustaceans (Gherghel et al. 2018; Sherratt et al. 2018).
Our study utilized correlative models to determine the relationships between sea snakes and environmental variables, but caution must be exercised in interpreting the results since correlative models cannot establish causality. Some correlations may reflect direct effects of environmental variables, while others may represent indirect relationships. We used MaxEnt, which can handle collinearity among explanatory variables; however, collinearity may still pose challenges when estimating the importance of explanatory variables (Smith and Santos 2020). The programmers of MaxEnt incorporated two different metrics (PC and PI) to evaluate the contribution of predictors to the model (Phillips 2011), although there is no consensus in the literature on which is more informative. Most studies use the PC, possibly because it appears first in the algorithm’s results. Halvorsen (2013) concluded that the PC is most informative, whereas (Searcy and Shaffer 2016) suggested that the PI is better for describing the biological properties of species. Our study provides insights into the environmental factors important for the distribution of sea snakes, but further research is necessary to establish causal relationships between these factors and the distribution of sea snakes, as well as to gain a better understanding of their ecology and behavior.
In summary, our results on the relative importance of environmental variables in shaping the distribution and potentially the abundance of sea snakes, are consistent with previous research on marine organisms and provide a valuable framework for developing effective conservation management plans for sea snakes.