The Great Salt Lake (GSL) is a unique hypersaline system with an understudied phytoplankton community supporting a critical zooplankton (brine shrimp) population which we study as part of our industry’s monitoring program. Determination of the phytoplankton by traditional microscopy is becoming logistically difficult for our program, but DNA metabarcoding can inexpensively and quickly generate a large volume of data on community assemblages while opening new directions of analysis. To determine if metabarcoding could replicate microscopy and expand the assessment of GSL phytoplankton in our monitoring program, a two-year 23S SSU rDNA metabarcoding and microscopy survey was conducted in 2017 and 2018. Community composition and relative abundances from each method were compared, and spatial and temporal assemblage changes from metabarcoding data were determined using non-metric multidimensional scaling.
Results/Conclusions
23S metabarcoding differed from microscopy in multiple taxonomic assignments and relative abundances. Dunaliella was the dominant chlorophyte in both methods, but while microscopy attributed 86% of community biovolume to this taxa, metabarcoding assigned only 33% of DNA sequences. Conversely, diatoms comprised 10% of biovolume but 57% of DNA sequences. A disparity between biovolume and sequence proportion was expected given prior phytoplankton studies utilizing different primers. However, metabarcoding analysis revealed seasonal and spatial patterns in assemblage and detected potential cryptic speciation within the lake’s dominant Dunaliella viridis, an unexpected result. Metabarcoding also enabled the examination of the gut content of brine shrimp, and we thereby detected a benthic-pelagic linkage with the lake’s vast microbialite fields. As end users of this phytoplankton analysis method, we have concluded that metabarcoding cannot yet replicate or replace microscopy, but it is complementary to it for the purposes of our monitoring program and will be an important tool in future research questions.