A comparison of methods used to monitor groundwater inundation of sea turtle nests

Sea turtle eggs are at risk of inundation and erosion throughout their incubation. Inundation reduces gas exchange necessary for proper embryonic development with prolonged exposure resulting in mortality. Management actions such as nest relocation may reduce this threat; however, they are often undertaken with incomplete information (e.g., tolerance of sea turtle embryos to inundation, and knowledge of the environmental differences between the original and final nest locations). Despite the need to understand the risk of sea turtle nest inundation, few studies measure inundation directly, and those that have, used PVC-based equipment with limited sampling resolution and measurement precision. To improve in situ inundation monitoring, we tested the use of electronic water level loggers (HOBO U20L-04) at loggerhead sea turtle nests, and compared costs, benefits, and limitations of this equipment to the PVC devices used in previous research. The HOBO loggers demonstrated > 90% correlation with the PVC inundation devices in inundation frequency for both experimental sites and incubating nests. PVC devices tended to overestimate inundation duration (24.7 +/- 5.0 h SE) and underestimate inundation severity (14.6% +/- 6.6% SE) compared to the HOBO loggers. The greater temporal resolution and measurement precision of the HOBO logger provided higher quality data pertaining to inundation stress in the nests during inundation events over the PVC devices. Small-scale studies of inundation tolerance and other physiological responses to inundation would benefit from this improved data quality; however, the cost of each unit and associated software and hardware may be prohibitive for some monitoring programs. The PVC devices are low cost and simple to mass-produce, lending their use for large-scale monitoring efforts to better inform relocation decisions and productivity assessments.