Swimming against the flow—Environmental DNA can detect bull sharks (Carcharhinus leucas) across a dynamic deltaic interface. Issue 1 (21st December 2020)

• Record Type: Journal Article
• Authors: Drymon, James Marcus; Schweiss, Katherine E.; Seubert, Emily A.; Lehman, Ryan N.; Daly‐Engel, Toby S.; Pfleger, Mariah; Phillips, Nicole M.
• Is Part Of: Ecology and evolution. Volume 11:Issue 1(2021)
• Page Start: 22
• Page End: 28
• Publication Date: 2020-12-21
• Subjects: eDNA -- elasmobranch -- estuary -- habitat use -- river; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.7101
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Human activities in coastal areas are accelerating ecosystem changes at an unprecedented pace, resulting in habitat loss, hydrological modifications, and predatory species declines. Understanding how these changes potentially cascade across marine and freshwater ecosystems requires knowing how mobile euryhaline species link these seemingly disparate systems. As upper trophic level predators, bull sharks ( Carcharhinus leucas ) play a crucial role in marine and freshwater ecosystem health. Telemetry studies in Mobile Bay, Alabama, suggest that bull sharks extensively use the northern portions of the bay, an estuarine–freshwater interface known as the Mobile‐Tensaw Delta. To assess whether bull sharks use freshwater habitats in this region, environmental DNA surveys were conducted during the dry summer and wet winter seasons in 2018. In each season, 5 × 1 L water samples were collected at each of 21 sites: five sites in Mobile Bay, six sites in the Mobile‐Tensaw Delta, and ten sites throughout the Mobile‐Tombigbee and Tensaw‐Alabama Rivers. Water samples were vacuum‐filtered, DNA extractions were performed on the particulate, and DNA extracts were analyzed with Droplet Digital™ Polymerase Chain Reaction using species‐specific primers and an internal probe to amplify a 237‐base pair fragment of the mitochondrial NADH dehydrogenase subunit 2 gene in bull sharks. One water sample collected during the summer in the Alabama River met the criteria for a positive detection, thereby confirming the presence of bull shark DNA. While preliminary, this finding suggests that bull sharks use less‐urbanized, riverine habitats up to 120 km upriver during Alabama's dry summer season. Abstract : Estuarine, deltaic, and freshwater ecosystems are connected by mobile species that can increase ecosystem resilience by linking these otherwise disparate habitats. However, monitoring populations of mobile link species across multiple, expansive habitats presents logistical challenges. In this study, we use environmental DNA to provide the first evidence of bull shark habitat use 120 km upriver in the Alabama River. While preliminary, our findings provide a basis for further study and demonstrate the usefulness of this technique across similarly dynamic environments.