MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12991

Developing an eDNA toolkit to quantify spawning events of the broadcast spawning sea scallop (Placopecten magellanicus): moving beyond fertilization assays

Skylar R. Bayer*, Peter D. Countway, Richard A. Wahle

*Email: skylar.bayer@noaa.gov

ABSTRACT: Broadcast spawners release their gametes into the water column for ‘chance’ fertilization events. However, detection of such events in near real-time is extremely difficult, but needed to improve fisheries and conservation management practices. It is practically impossible to distinguish the gametes of many species by microscopy; therefore DNA-based techniques are preferable to detect and quantify gametes from field-collected plankton samples. We developed a quantitative PCR (qPCR) approach for detection and quantification of broadcast spawning events in marine environmental DNA (eDNA) samples. We applied this approach to a commercially valuable broadcast spawning bivalve species, the sea scallop (Placopecten magellanicus). Our approach includes (1) sequencing the Internal Transcribed Spacer (ITS) region, (2) developing a novel species-specific probe and primer set (3) testing the probe and primer set on a dilution series of sea scallop sperm to quantify the relationship between gamete abundance and DNA copy number, and (4) conducting dockside field tests of our method on plankton samples adjacent to naturally spawning sea scallops. Quantitative PCR revealed a clear relationship between DNA copy number and P. magellanicus sperm cell abundance, indicating that this method is reliable for detecting sperm release by male scallops during spawning events. Plankton samples collected during the scallop spawning season revealed spikes of scallop eDNA in both the < 20 (sperm) and > 20 µm (possible eggs) particle size-fractions. This method holds great potential to provide more efficient estimates of the timing, magnitude, and spatial scale of reproductive events than conventional methods for a wide range of broadcast spawners.