Species‐specific biomass estimation from gene copy number in metazoan plankton

Abstract

AbstractDespite the importance of early life‐history stages to ecosystem processes, challenges in the identification of the larval stages of species continue to slow progress in understanding the dynamics of marine ecosystems. A quantitative polymerase chain reaction‐based method was developed and tested for estimating the species‐specific biomass of juvenile copepods through targeted measurements of mitochondrial cytochrome c oxidase subunit I (mtCOI) gene copies in size‐fractionated, mixed‐species plankton samples. The assays are species‐specific, amplifying a single product in the presence of focal‐species DNA at levels as low as 2 pg total DNA, and in mixed‐species samples where the focal species represented <1% of total DNA. Tests comparing mtCOI copy number to measurements of biomass across developmental stages found a robust linear relationship across a five order of magnitude range in animal biomass and DNA copy number (r2 = 0.998). These results demonstrate that quantification of DNA copy number can be used to obtain estimates of species‐specific biomass for metazoan plankton, which could transform population and community dynamics studies that include early life history stages.