Phototrophic Picoplankton in Lakes Huron and Michigan: Abundance, Distribution, Composition, and Contribution to Biomass and Production

Abstract

The phototropic picoplankton communities of Lakes Huron and Michigan were studied from 1986 through 1988. Abundances in the surface-mixed layer ranged from 10 000 to 220 000 cells∙mL−1 with a seasonal maximum during the period of thermal stratification. During thermal stratification, maximum abundances were generally found within the metalimnion/hypolimnion at depths corresponding to the 0.6–6.0% isolumes. The picoplankton community was dominated by single phycoerythrin-containing (PE) Synechococcus (59%) with lesser amounts of chlorophyll fluorescing cells (21%), PE colonial Synechococcus-like cells (11%), other PE colonial Chroococcales (6%), and other cells (3%). Single PE Synechococcus was abundant throughout the year whereas chlorophyll-fluorescing and colonial cyanobacteria were more abundant during the periods of spring isothermal mixing and summer stratification, respectively. Picoplankton accounted for an average of 10% (range 0.5–50%) of phototrophic biomass. Phototrophic organisms that passed 1-, 3-, and 10-μm screens were responsible for an average of 17% (range 6–43%), 40% (21–65%), and 70% (52–90%) of primary production. Maximum contributions of < 1, < 3, and < 10 μm size fractions occurred during the period of thermal stratification. Primary production by phototrophic picoplankton was found to equal production in the < 1 μm size fraction.

The importance of zooplankton‐protozoan trophic couplings in Lake Michigan

“…Average estimates of macrozooplankton clearance rates on nano-and microprotozoa determined from our experiments [3.53 and 2.52 ml (pg dry wt)) ' d-l] were at the high end of the range for rates reported on epilimnetic phytoplankton in Lake Michigan [range, O-2.6 ml (pg dry wt-' d-l, Scavia and Fahnenstiel 19871. Also., clearance rates of smaller Hnano cells (avg., 4.1; SD = 1.9) by macrozooplankton determined here were almost twofold higher than clearance rates measured for phytoplankton both in surface and deep regions of Lake Michigan Fahnenstiel and Scavia 1987).…”

Have we overlooked the importance of small phytoplankton in productive waters?

“…Also, the assumption that filter pore size is accurate and consistent in configuration on filters is not always robust (see Stockner et al 1990). Overestimation of primary produc:ion (14C incorporation) by small cells can result from breakage or direct passage of larger labeled cells that subsequently pass small pore-size (l-, 2-, or 3-pm poresize) filters and inflate estimates of picoplankton production (Fahnenstiel et al 1994). The filter-clogging artifact we have identified here becomes a problem when one assumes that the efficiency of cell passage among various screens is equal.…”

“…Although this method is laborious, it is not prone to artifacts encountered by filter fractionation of incorporated 14C isotope to estimate size-specific primary production (e.g. Fahnenstiel et al 1994).…”

Particle Transport, Nutrient Cycling, and Algal Community Structure Associated with a Major Winter-Spring Sediment Resuspension Event in Southern Lake Michigan

“…Bacteria, picocyanobacteria, and nanoflagellates (preserved with 4% glutaraldehyde) were enumerated and their linear dimensions were measured under a Leitz Laborlux fluorescent microscope (magnification × 1,000) as described by Bratbak (1993), Fahnenstiel and Carrick (1992), and Sherr et al (1993), respectively. Non-diatom phytoplankton and ciliates (preserved with 1% acid Lugols iodine) were counted in settling chambers under a Wild phase-contrast inverted microscope (125-500×).…”