The size distribution of plankton biomass in a large lake and its seasonal variability

Abstract

Biomass size spectra were calculated from comprehensive microscopic assessment of plankton organisms in large, deep Lake Constance (Bodcnsec). They revealed an approximately constant size distribution of biomass from bacteria (10 I4 g C cell-') to crustaceans ( 1O-4 g C ind.-'), resembling distributions found in open marine systems (seasonal average). Size ranges without detectable biomass as reported from other lakes did not exist. External perturbations, and size and depth of the pelagic zone, but not the type of habitat (marine vs. limnetic) were suggested as crucial factors influencing the shape of the biomass size distribution. The fit of the normalized biomass size spectrum to a straight line with a slope of -1 .OO was very close (rZ = 0.98), indicating a decrease of abundance per size class N proportional to the increase of body weight w (N cc w-l). Seasonal variation of biomass per size class was strongly related to body weight. It was largest for organisms with generation times of about 1 yr. Slopes of normalized biomass size spectra were steep in early spring (-1.16) indicating a dominance of small organisms and a low transfer cfficicncy to larger organisms. From spring to early summer, the size distribution of organisms shifted toward larger organisms (slope up to -0.94). The seasonal changes of the size spectra support the idea that, due to differences in the intrinsic reaction times of differently sized organisms, varying environmental conditions produce less regularly shaped actual size spectra, if not averaged over a period longer than the external fluctuations.Biomass size spectra (i.e. frequency distributions of biomass arrayed by individual weights) provide an important contribution to the search for generalization in pelagic ecosystems. Biomass size spectra are constructed by allocating all organisms (particles) into size classes according to their individual body mass (size) and computing the total biomass,per size class. Hence, the required data base is close to the form in which the raw data are obtained.The first biomass size spectra were obtained by Sheldon et al. ( 1972) in open oceans and comprised a restricted size range of the pelagic community based on meaAcknowledgments

Trophic Structure and Carbon Flow Dynamics in the Pelagic Community of a Large Lake

“…Original measurements of body sizes were converted to units of C using measurements from Lake Constance or the literature. References and further information on sampling and eounting teehniques and the eomputations of biomass size distributions are given by Gaedke (1992).…”

“…The sampling site is located in the northwestern fordlike arm whieh has no major in-or outflows. Pelagie species composition, productivity, and population dynamics, as weIl as ecosystem properties, have been studied in detail throughout the last deeade Ce.g., Tilzer and Beese (1988), Güde (1990), Weisse et al (1990), GeIler et al (1991, Müller et al (1991), and Gaedke (1992. The C flow within and between the mierobial and classieal food webs was investigated using mass-balanced C flow diagrams and network theory (Gaedke and Straile, 1994a).…”

Biomass Size Spectra and Plankton Diversity in a Shallow Eutrophic Lake

“…organisms were found in each sizeclass) and that biomass per logarithmically scaled size-class was roughly equal or slightly decreasing with body mass. When this hypothesis was tested in other habitats, more irregular spectra, with or without discontinuities, prevailed under bloom conditions both in marine and limnetic systems (SPRULES and MUNAWAR, 1986;WITEK and KRAJEWSKA-SOLTYS, 1989;GAEDKE, 1992;GAEDKE and STRAILE, 1998;TITTEL et al, 1998), in a small high mountain lake (RODRIGUEZ et al, 1990) and in lakes with extreme environmental conditions (GASOL et al, 1991;STEINBERG et al, 1998a, b). More recently, time series of limnetic size distributions based on weekly sampling and microscopic enumeration enabled the first detailed studies of how the slope and shape of the size distributions reflect seasonal plankton community compositions in stratified lakes.…”

A regime shift from macrophyte to phytoplankton dominance enhances carbon burial in a shallow, eutrophic lake

“…Specifically, Telesh et al (1998) was applied for rotifers, Mü ller and Geller (1993) for ciliates, and Dumont et al (1975) for crustaceans. A C content of 50% dry weight (dw) was assumed (Gaedke 1992 and references therein).…”