Plankton filaments

In the context of plankton dynamics an interesting development that has some common ideas with the KiSS approach but introduces a new and important element is described in Martin (2000). The idea is that dispersion of a patch is not only controlled by eddy diffusivity, but also by the geometric characteristics of the mean flow. It turns out that if an incompressible fluid flow induces dispersion in one direction it necessarily produces convergence in another, to conserve the fluid volume. This was already exploited in Sect. 2.7.1, and includes the ingredient of advection, in addition to the reaction-diffusion processes which are the subject of this Chapter. Nevertheless, since this case can be analyzed easily and extends the KiSS model, we consider it here. 

Martin (2000) proposes the following model to describe the transverse profile of a phytoplankton filament  

This is exactly the filament model (2.87) except for the linear growth term. There are two differences with respect to the KiSS model. One is the possible time-dependence of the growth rate //(t), which is a simplified linear representation of nonlinear interactions and predation on phytoplankton following the initial stage of growth. The other is the advective term —AxdxP that models a local strain. 

It is again a Gaussian with time-dependent height but characteristic width Id = y/D/X. At variance with the KiSS approach, the lateral scale of the filament is not controlled by some externally imposed size of the suitable water, but by the competition between diffusion and advection. It is somewhat surprising that the biological growth rate does not affect the filament width in this model. As we will see in Chapter 7 this feature is not shared by more realistic models. 

The general solution in the unbounded line can also be found from (2.91)  

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The photo synthetic aquatic biomass comprises cyanobacteria (formerly called blue-green algae), planktonic, filamentous and macrophytic algae, and vascular macrophytes. The net productivity of the floodwater depends on the level of primary production by the photosynthetic biomass versus its consumption by grazing animals, particularly cladocerans, copepods, ostracods, insect larvae and molluscs. Their role will change as the canopy develops and at a leaf area index of about 6-7 there will be no more photosynthetically active radiation available to them. 

Carpenter, E. J., and Janson, S. (2001). Anabaena gerdii sp. nov., a new planktonic filamentous cyanobacterium from the South Pacific Ocean and Arabian Sea. Phycologia 40, 105—110. 

Roach (rutilus rutilus), a medium-sized cyprinid fish, is a planktonic and benthic species, feeding mainly on cladocerans (D. longispina), detritus, plant debris, amphipods (Echinogammarus sp.), filamentous algae, and ostracods. Roach can thrive on poor quality, even polluted water and displays more capacity of adaptation to different kinds of food than rudd [62]. 

This is interesting for fragile objects such as mammalian cells [13], which should not be squeezed between glass surfaces, and for motility experiments as the displacement of the cells is not limited vertically. The largest available magnification, depending upon the ocular-lens combination is about x 1500. This value limits the observation of the smallest cells such as non filamentous bacteria (E. coli) or plankton. 

With the exception of filamentous cyanobacteria, fluorescence from biliproteins such as phycoer) hrin and/or phyco-cyanin is not observed in samples taken by fine plankton nets. 

Neufeld et al. (2002a) have shown that this behavior can be explained by the interplay between excitable plankton population dynamics and chaotic flow, similarly to the excitable behavior described in the previous section. In a chaotic flow a steady bloom filament profile can be generated, that does not decay until it invades the whole computational domain as an advectively propagating bloom. The condition for the existence of the steady bloom filament solution in the corresponding one-dimensional filament model is that the rate of convergence, quantified by the Lyapunov exponent, should be slower than the phytoplankton growth rate, but faster than the zooplankton reproduction rate. In this case the phytoplankton does not became diluted by the flow and the zooplankton is thus kept at low concentration unable to graze down the bloom filament. 

A.P. Martin. On filament width in oceanic plankton distributions. J. Plank. Res., 22 597, 2000. 

Many of the species living around thermal springs are involved in the precipitation of lime to form travertine. Filamentous species of Anabaena, Os-cillatoria and Spirulina are frequently found both floating in water (planktonic) or moving freely over the surface of underwater sediments (epipelic) and high concentrations of filaments appear bluish-green or black. 

Repka, S., M. van der Vlies, and J. Vijverberg. 1998. Food Quality of Detritus Derived from the Filamentous Cyanobacterium Oscillatoria Limnetica for Daphnia Galeata. Journal of Plankton Research 20 (ll) 2199-2205. 

Filamentous bacteria are rarely measured in planktonic counts and grow poorly on Petrifilms. Many will not grow on artificial media at all. Filamentous bacteria form major deposit problems (sessile population) on neutral to alkaline machines. 

The Centrales are generally planktonic because the discoid structure makes it possible to increase the surface area/volume ratio, and thus to increase buoyancy in fresh or salty water. Pennales are generally benthic because their lengthened structure does not permit this buoyancy. Although diatoms are all unicellular, filamentous colonial forms also exist, the length of which can attain 2 mm. A simplified classification of the marine diatoms is presented in Table 9.1 (the main genera for which research into their metabolites has been conducted are shown in bold type). 

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