title: A comparison of morphological and molecular-based surveys to estimate the species richness of Chaetoceros and Thalassiosira (bacillariophyta), in the Bay of Fundy.
abstract: The goal of this study was to compare the ability of morphology and molecular-based surveys to estimate species richness for two species-rich diatom genera, Chaetoceros Ehrenb. and Thalassiosira Cleve, in the Bay of Fundy. Phytoplankton tows were collected from two sites at intervals over two years and subsampled for morphology-based surveys (2010, 2011), a culture-based DNA reference library (DRL; 2010), and a molecular-based survey (2011). The DRL and molecular-based survey utilized the 3' end of the RUBISCO large subunit (rbcL-3P) to identify genetic species groups (based on 0.1% divergence in rbcL-3P), which were subsequently identified morphologically to allow comparisons to the morphology-based survey. Comparisons were compiled for the year (2011) by site (n = 2) and by season (n = 3). Of the 34 taxa included in the comparisons, 50% of taxa were common to both methods, 35% were unique to the molecular-based survey, and 12% were unique to the morphology-based survey, while the remaining 3% of taxa were unidentified genetic species groups. The morphology-based survey excelled at identifying rare taxa in individual tow subsamples, which were occasionally missed with the molecular approach used here, while the molecular methods (the DRL and molecular-based survey), uncovered nine cryptic species pairs and four previously overlooked species. The last mentioned were typically difficult to identify and were generically assigned to Thalassiosira spp. during the morphology-based survey. Therefore, for now we suggest a combined approach encompassing routine morphology-based surveys accompanied by periodic molecular-based surveys to monitor for cryptic and difficult to identify taxa. As sequencing technologies improve, molecular-based surveys should become routine, leading to a more accurate representation of species composition and richness in monitoring programs.
authors.affiliation: Biology, University of New Brunswick, Fredericton, New Brunswick, Canada.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Hamsher
authors.forename: Murielle M
authors.initials: MM
authors.lastname: LeGresley
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Martin
authors.forename: Gary W
authors.initials: GW
authors.lastname: Saunders
mesh_terms: D061006:Bays; D017377:Diatoms / Q000145:classification / Q000235:genetics*; D017753:Ecosystem; D010802:Phylogeny