Vinay Udyawer, Colin A. Simpfendorfer, Michelle R. Heupel, Timothy D. Clark
Resources within a given environment (e.g. shelter, prey) are often not the same between different habitats. Therefore how animals move and select habitats within their environment tend to incorporate strategies to maximise the benefits they gain from different habitats while minimising the amount of energy they expend. The proficiency with which they use these strategies can ultimately determine their ability to react to environmental change or to natural and man-made threats. Measuring oxygen consumption rates during different levels of activity in animals can provide useful insight into how much energy they spend, but measuring this directly in their natural environment is logistically difficult. This is particularly true when we consider air-breathing aquatic animals. Recent advances in biotelemetry have allowed us to use animal-borne accelerometers to measure body acceleration as a reliable proxy for how free-living animals expend energy related to activity in the wild, and provide useful insights into their energy budgets.
Sea snakes are one such group of air-breathing ectotherms (cold-blooded animals) where we lack fundamental information on energy budgets. This group of animals have undergone significant recent global declines in locations around the world that have been considered marine snake biodiversity hotspots (e.g. Western Australia, the Great Barrier Reef, New Caledonia). The causes of these declines are currently unknown, however factors like increasing water temperatures, frequency of heatwaves and human activities (e.g. trawl fishing, coastal development) are considered major threats for these populations. This study uses animal-borne accelerometers alongside bimodal respirometry experiments (i.e. involving oxygen uptake from both water and air) to understand how varying thermal environments influence energy expenditure in sea snakes. This information is also used to accurately calculate estimates of field metabolic rates in sea snakes over daily and seasonal timescales, and to examine how sea snakes partition energy between multiple habitats within their natural environment.
We found that over a daily timescale, circadian activity patterns influenced short-term field metabolic rates. Whereas over a seasonal scale, water temperatures drove long-term field metabolic rates. This study also illustrated how sea snakes partitioned energy between different habitats within a near-shore environment, and consequently influenced their movements and habitat selection.
Photo caption: Releasing an Elegant sea snake (Hydrophis elegans) to collect field data after implantation of acoustic accelerometer transmitter and calibration experiments. Calibration experiments in the lab defined relationships between body acceleration, oxygen consumption and water temperature that allowed for accurate estimates of field metabolic rates from field data. Photo by Eric Nordberg