Plankton Size Spectra Research Articles

Analysis of plankton size spectra irregularities in two subtropical shallow lakes (Esteros del Iberá, Argentina)

Biomass irregularities in the plankton size spectra of two subtropical shallow lakes have been quantified assuming the classical observed generalities of the size spectra. During a seasonal cycle, three main functional size ranges determined the allocation of the spectra irregularities: microbial food web, nanoplankton–microplankton autotrophs, and herbivorous organisms. The structural adjustments within these trophic positions responded to the internal competition between functional guilds, mainly as the result of size-based characteristics related to the ability to eat and the susceptibility to be eaten. Despite the existence of a typical spectrum undulation resulting from self-organization (well-defined trophic positions, limnetic–benthic interaction), the biomass irregularities were an indicator of the main interactions disturbing the steady state. The mechanisms responsible for the irregularities operated jointly at ecosystem and individual levels. Thus, the irregular spectra of the eutrophic Laguna Iberá suggested a strong top-down control through cascade effects. Specific properties of peculiar organisms like filamentous cyanobacteria contributed to hold these stable irregularities. The higher spectrum regularity of the meso-oligotrophic Laguna Galarza emerged from a more balanced flow of biomass along the food chain.

Cross-scale ecological dynamics and microbial size spectra in marine ecosystems.

Evaluating the component features of 'scaling' planktonic size spectra, commonly observed in marine ecosystems, is crucial for understanding the ecological and evolutionary processes from which they emerge. Here, we develop a theoretical framework that describes such spectra in terms of the size distributions of individual species, and test it against actual datasets of microbial size spectra from the Atlantic Ocean. We describe characteristics of size probability distributions of component species that are sufficient to support the observational evidence and infer that, when a power law describes the community size spectrum (thus suggesting critical self-organization of microbial ecosystem structure and function), a related power law links the total number of individuals of a given species to its mean size.

Stable model structures for representing biogeochemical diversity and size spectra in plankton communities

There is a fundamental duality in the way we view planktonic communities. On one hand, we see these communities as composed of a diverse mixture of taxonomically and biogeochemically distinct species; pelagic ecosystem models capable of predicting the ocean's role in the global carbon cycle will need to resolve these multiple plankton taxa. However, we have also come to appreciate that superimposed on this diversity are regular patterns of size structure, where plots of abundance within size classes typically show a power-law dependence on size. A truly complete model descrip- tion of planktonic community structure must reflect both aspects of this duality. Here I examine two classes of ecosystem models that are capable of representing this duality. The first structure is based on multiple (n) couplets of phytoplankton (P) and zooplankton (Z) (an 'n(PZ)' model). Within certain regions of parameter space, this model structure can produce anomalous oscillatory behaviors, the mathematical origin of which is explored in detail. I then examine an alternative food web structure in which total herbivore abundance is represented by a single state variable, G, and where grazing pressure is distributed among taxa in proportion to their abundances. This '(nP)G' system is stabilized by the redistribution of grazing intensity among taxa in response to changes in their densities. This 'distributed grazing' model also naturally produces size spectra of plankton abundance; this last observation argues that the model with distributed grazing can help in uncovering and repre- senting the mechanistic basis for the genesis and maintenance of planktonic size spectra of phyto- plankton and bacteria.

A comparison of lakes and lake enclosures with contrasting abundances of planktivorous fish

Experimental manipulations of planktivorous fish in large enclosures produced plankton communities comparable to those in lakes with contrasting abundances of planktivorous fish. Total epilimnetic phosphorus (TP), its distribution among five size-classes of dissolved ( 200 u-m), phosphate turnover time, water clarity (Secchi depth) and phytoplankton biomass (chlorophyll a) were measured for two summers in eight large enclosures where planktivorous fish (1 + yellow perch) and nutrients (N and P) were added in a 2 x 2 factorial design. These parameters were also measured in two meso-eutrophic kettle lakes, Lake St George and Haynes Lake, containing low and high abundances of planktivorous fish, one of which was the lake (Lake St George) containing the enclosures. Comparable data were also collected from three oligo-mesotrophic lakes in central Ontario. In both the enclosures and the lakes, intense planktivorous fish predation was associated with increased TP, decreased abundance of larger zooplankton and mesoplanktonic PP (>200 p-m), increased pico- and nanoplanktonic PP (1-20 (Jim), increased phosphate limitation (faster turnover time), increased chlorophyll a and reduced water clarity. Slope parameter, an index of plankton size-spectrum, was correlated with phosphate turnover time and Secchi depth among enclosures, and the data from all five lakes conformed to these empirical relationships. Fertilization of enclosures produced increased variability in the relationship among the variables. Our 2 years of experiments produced qualitatively similar treatment effects, but the magnitude of the effects was not similar for all parameters. We suggest that the responses of plankton communities and associated parameters to planktivore predation that we observed in large experimental enclosures are basically similar to those in the lakes we studied, and that enclosures are an important tool in understanding complex interactions in aquatic systems.

Effects of fertilization and planktivorous fish (yellow perch) predation on size distribution of particulate phosphorus and assimilated phosphate: Large enclosure experiments1

Nutrients, planktivorous fish (1 + yellow perch), or both were added to eight large enclosures in a 2 × 2 factorial design. The size distributions of particulate phosphorus (PP) and assimilated 32PO43− and PO43− turnover times were determined from June through August by filter fractionation. The amount of PP >200 µm (mesoplankton) increased with fertilization and decreased with addition of fish, but the amount of PP in nanoplankton (3–20 µm) and large picoplankton (1–3 µm) showed opposite results. Fertilization and addition of fish had interacting effects on the PP in microplankton (20–200 µm). Microplankton phosphorus was higher with fish in unfertilized enclosures and lower with fish in fertilized enclosures. Slopes estimated from the relationship between the proportion of PP retained and the logarithm of filter size were used to characterize the size spectra of plankton and were lower with fertilization and steeper with addition of fish. They were negatively correlated with PO43− turnover time, reflecting that plankton communities dominated by small cells were more nutrient limited. The slope parameter was also significantly correlated with water clarity (Secchi depth) and algal biomass (Chl a), but particle size distribution contributed to water clarity independent of biomass or pigment concentration. This slope parameter can be used as a convenient indicator of plankton size spectra and trophic interactions in freshwater ecosystems.

Plankton Size Spectra in Relation to Ecosystem Productivity, Size, and Perturbation

Quantification and comparisons of the structure of open-water plankton communities from 25 inland lakes of Ontario, from the Laurentian Great Lakes Superior, Huron, St. Clair, Ontario, and Erie, and from the Central Gyre in the North Pacific Ocean were made on the basis of the normalized biomass size spectrum. Residual variation around the fitted straight lines (corresponding to a theoretical steady state) was least for the large, oligotrophic Lake Superior and the North Pacific Gyre and greatest for eutrophic Saginaw Bay and shallow Lake Erie, suggesting progressive departure from steady-state conditions with increasing system productivity. The slopes of the normalized spectra decrease with increasing eutrophy, indicating that nannoplankton abundances are similar in all communities studied, but that associated zooplankton abundances vary by 2.5 orders of magnitude. Our results suggest that parameterization of particle-size models for prediction of potential fish production must be adjusted according to the size and productivity of the ecosystem, and that routine monitoring of communities by the normalized biomass spectrum could provide early warning of nutrient or toxic stress in aquatic ecosystems.