Changes in coastal Gopher Tortoise (Gopherus polyphemus) burrow characteristics and density following hurricane events in Northeast Florida, USA: Implications for conservation planning

Abstract

Abstract The Gopher Tortoise, Gopherus polyphemus is iconic, yet threatened throughout its range in the southeastern United States. It is a burrowing, herbivorous tortoise whose upland habitats have been greatly reduced by habitat destruction, fragmentation and/or reduction in quality due to anthropogenic changes in the disturbance regimes, such as fire, that are necessary to maintain quality habitat. Importantly, Gopher Tortoises are well documented keystone species supporting numerous conspecifics that are dependent upon or regularly use their burrows. While this species has been much studied in its inland habitats, it also thrives in coastal sand dune environments where little is known about its behavior, ecosystem role or conservation status. Coastal natural areas in the state of Florida, USA have been significantly reduced by human activity, and are now additionally threatened with accelerated sea level rise and more frequent and intense storms. We collected Gopher Tortoise burrow location, abundance, width and activity data in 2016 for a coastal population within northeast Florida, protected within the northern component of the Guana Tolomato Matanzas National Estuarine Research Reserve. Soon after our burrow survey was completed in 2016, Hurricane Matthew heavily impacted our study area that fall. In order to determine the degree to which this Gopher Tortoise population might have been impacted by the hurricane, we began re-surveying burrows in 2017 but were interrupted by another Hurricane, Irma, in 2017. We completed the post-hurricanes burrow surveys in 2018. When comparing pre-and post-hurricanes surveys, we found that habitat was lost and burrow density increased. The relative proportion of burrows categorized as “active” increased, while “inactive” and “abandoned” burrows decreased. Furthermore, burrow abundance decreased by 10% following these back-to-back hurricane events. We infer that individual Gopher Tortoises mostly abandoned low elevation burrows at risk of hurricane-related storm surge and relocated to higher elevation, unused (or “inactive” and “abandoned”) burrows. Such relocation, combined with significant loss of previously inhabited lower elevation habitat could explain the post-storm increase in burrow density and the proportional changes in burrow activity classification. However, as resilient as this population may be, it is running out of room due to sea level rise and habitat loss and fragmentation. Such implications for this and other species should be considered in conservation planning for coastal species of concern.