Planktonic microbes in the Gulf of Maine area

Abstract

In the Gulf of Maine area (GoMA), as elsewhere in the ocean, the organisms of greatest numerical abundance are microbes. Viruses in GoMA are largely cyanophages and bacteriophages, including podoviruses which lack tails. There is also evidence of Mimivirus and Chlorovirus in the metagenome. Bacteria in GoMA comprise the dominant SAR11 phylotype cluster, and other abundant phylotypes such as SAR86-like cluster, SAR116-like cluster, Roseobacter, Rhodospirillaceae, Acidomicrobidae, Flavobacteriales, Cytophaga, and unclassified Alphaproteobacteria and Gammaproteobacteria clusters. Bacterial epibionts of the dinoflagellate Alexandrium fundyense include Rhodobacteraceae, Flavobacteriaceae, Cytophaga spp., Sulfitobacter spp., Sphingomonas spp., and unclassified Bacteroidetes. Phototrophic prokaryotes in GoMA include cyanobacteria that contain chlorophyll (mainly Synechococcus), aerobic anoxygenic phototrophs that contain bacteriochlorophyll, and bacteria that contain proteorhodopsin. Eukaryotic microalgae in GoMA include Bacillariophyceae, Dinophyceae, Prymnesiophyceae, Prasinophyceae, Trebouxiophyceae, Cryptophyceae, Dictyochophyceae, Chrysophyceae, Eustigmatophyceae, Pelagophyceae, Synurophyceae, and Xanthophyceae. There are no records of Bolidophyceae, Aurearenophyceae, Raphidophyceae, and Synchromophyceae in GoMA. In total, there are records for 665 names and 229 genera of microalgae. Heterotrophic eukaryotic protists in GoMA include Dinophyceae, Alveolata, Apicomplexa, amoeboid organisms, Labrynthulida, and heterotrophic marine stramenopiles (MAST). Ciliates include Strombidium, Lohmaniella, Tontonia, Strobilidium, Strombidinopsis and the mixotrophs Laboea strobila and Myrionecta rubrum (ex Mesodinium rubra). An inventory of selected microbial groups in each of 14 physiographic regions in GoMA is made by combining information on the depth-dependent variation of cell density and the depth-dependent variation of water volume. Across the entire GoMA, an estimate for the minimum abundance of cell-based microbes is 1.7×10(25) organisms. By one account, this number of microbes implies a richness of 10(5) to 10(6) taxa in the entire water volume of GoMA. Morphological diversity in microplankton is well-described but the true extent of taxonomic diversity, especially in the femtoplankton, picoplankton and nanoplankton--whether autotrophic, heterotrophic, or mixotrophic, is unknown.

Figure 1. Gulf of Maine Area map.

Fourteen physiographic regions are defined for this study (Text S1). The shaded bathymetry is from United States Geological Survey 15 arc sec data used in the hypsometric calculations. High-resolution data were not available for the portion (2%) of the study area that is not shaded.

Figure 2. Abundance of microbial groups on the Scotian Shelf.

(A) Bacteria (prokaryotes excluding cyanobacteria); (B) Chlorophyll a; (C) Synechococcus; (D) Picoeukaryotic phytoplankton; (E) Small nanophytoplankton; (F) Large nanophytoplankton. Data are from the Atlantic Zone Monitoring Program and binned into 5 m depth intervals. Profiles indicate average values and standard deviations from a network of stations on the Scotian Shelf sampled mainly in the spring and autumn from 1997 to 2010.

Figure 3. Depth-varying correlations of microbial abundance versus chlorophyll a concentration in the Gulf of Maine.

(A) Map of 3 stations in Jordan Basin, 1 station in Crowell Basin, and 2 stations in the Northeast Channel. Samples were collected in the upper 200 m from June 13–16, 2005 during the Discovery Corridor cruise. (B) Bacteria; (C) Synechococcus; (D) Picoeukaryotic phytoplankton; (E) Small nanophytoplankton; (F) Large nanophytoplankton. Microbial abundance in units of log cells ml-1; chlorophyll a concentration in units of log mg m^-3.