The winner goes to: A comparison of techniques to identify and quantify bivalve larvae in environmental samples in Washington State

Reliable detection and quantification of bivalve larvae during critical life stages is crucial in forecasting population abundance, recruitment, behavior, and dispersal. Therefore, it is scientifically and commercially valuable to develop an efficient method to quantify larval presence and abundance. Commonly used methods for approximating larval abundance involve distinguishing morphological differences between bivalve species in environmental plankton samples (EPS) by microscopy. This method is problematic during earlier stages of larval development and rely on high amounts of expertise in bivalve larvae identification. Most recently, approaches using TaqMan probe-based multiplex real-time polymerase chain reaction (RT-PCR) to quantify copies of DNA in comparison to a standard curve of known larvae has been successfully applied to cultivated larval samples. However, few studies have performed comprehensive comparisons of these methods using EPS. In the present study, assays to determine absolute quantification using a standard curve of the Pacific geoduck clam (Panopea generosa), Pacific oyster Crassostrea gigas), Olympia oyster (Ostrea lurida), and Manila clam (Venerupus phillipinarum) were developed and compared to microscopy techniques using morphological traits of the same species in two pulses of EPS at four relevant sites throughout Washington State. Preliminary results indicate the resourcefulness of using TaqMan chemistry to detect larval presence in known amounts of cultured larvae spiked in mock-up plankton samples as well as the presence of bivalve larvae in collected EPS. We predict that high-throughput RT-PCR will prove to be less time consuming and more reliable than microscopy in quantifying species specific abundances in EPS