Assessing the Occurrence of Trichechus manatus latirostris in Mobile Bay, Alabama Using eDNA

In the past several decades Florida manatees (Trichechus manatus latirostris) have begun to expand their summer range into the northern Gulf of Mexico. Because this is a recent occurrence, not much is known about their habitat use and distribution in this region. Citizen-sourced sighting data suggests that Florida manatees frequent subembayments of Mobile Bay, Alabama, reaching a sighting peak in August. To assess the occurrence of manatees in this area environmental DNA surveys were used from winter (February 19-20) and summer (August 21-22) of 2018. At each of the 21 sites ranging from the mouth of Mobile Bay, to the Mobile-Tensaw Delta, Mobile-Tombigbee River, and Tensaw-Alabama River, 5 × 1 L water samples were collected. An additional water sample was collected from an ex situ experiment to gain a positive eDNA sample. This was done by adding feces and flesh from a deceased Florida manatee then collecting the water sample 30 minutes later. All water samples were vacuum-filtered, extracted for DNA, and run on Droplet Digital™ Polymerase Chain Reaction. A previously developed ddPCR assay was used to amplify a 69-base pair segment of the cytochrome b gene. The assay was able to detect 77.2 copies/µL of target DNA in the positive eDNA sample, 1.180 copies/µL in the 1:10 dilution, and 0.211 copies/µL in the 1:100 dilution of this sample. One summer field sample met one out of three criteria while another met two out of three criteria for a positive detection. There was evidence of contamination in several negative control samples that highlights the importance of negative controls in eDNA experiments