The significance of autotrophic and heterotrophic picoplankton in hypertrophic ecosystems

Abstract

Hypertrophic aquatic ecosystems are biologically important because they represent an environment where homeostatic mechanisms are strongly reduced and extreme oscillations occur in physical and chemical parameters as well as in the growth of many planktonic organisms. Hypertrophic lakes may represent not only the ultimate state of eutrophication, but also systems where abundance and production of picoplanktonic organisms (0.2–2 μm in diameter) may theoretically be greatest. In this review we examined the microbial ecology literature for studies on hypertrophic lakes and assessed the significance of heterotrophic bacteria (BACT) and autotrophic picoplankton (APP). Our main conclusions are as follows: (a) The relative contribution of APP to total phytoplankton biomass is strongly reduced in hypertrophic systems. (b) The absolute abundance and biomass of APP are highly variable among these systems; depending mainly on differences in light quality and quantity, the existence of nitrogen limitation and presence of pollutants. (c) The abundance of BACT does not increase as rapidly as algal biomass with increasing trophy. (d) A clear dichotomy exists between lakes dominated by Microcystis where bacterial biomass and production are relatively low, and Planktothrix‐dominated lakes where bacterial biomass and production are high. (e) Bacterial production per unit biomass tends to increase from oligotrophic to hypertrophic systems supporting the previous hypothesis that bacteria do not play a lesser role in lake metabolism at the upper end of the trophic scale. In general, however, our knowledge of the microbial ecology of hypertrophic systems has advanced very little since the 1980s, largely because most studies of these systems have focused on their remediation.

Diel and seasonal variations in bacterioplankton production in a hypertrophic shallow lagoon

“…Similarly, en hanced LIR and TIR under artificial light were found in littoral sea waters (Ruiz-González et al 2012). In the present study, in which only PAR was taken into account, both LIR and TIR in the light were generally slightly higher than in the dark, in accordance with the findings of Sommaruga & Robarts (1997) and Ruiz-González et al (2012). Nonetheless, our results indicate a possible interaction between light and other parameters.…”

“…Lindell et al (1996) described inhibition or no effect of sunlight on LIR in 5 oligotrophic lakes in southern Sweden, and inhibitory effects of full solar radiation on LIR and TIR were described in a mesotrophic estuary in Florida (Aas et al 1996), which in part might have been due to ultraviolet radiation. However, higher TIR under light than under dark conditions were observed in a hypertrophic lake (Sommaruga & Robarts 1997). Similarly, en hanced LIR and TIR under artificial light were found in littoral sea waters (Ruiz-González et al 2012).…”

“…The significant subsidies of allochthonous material may be one plausible explanation for our inability to distinguish the impact of autochthonous DOC on the occurrence of diel cycles in productive waters (Gasol et al 1998). Even more profound gaps in our knowledge exist in regard to the daily variations, the seasonal patterns, and the general contribution of BP production in shallow hypertrophic 'hypereutrophic' lakes (Sommaruga & Robarts 1997, Auer et al 2004, Tammert et al 2005, which typically represent the final stage of eutrophication. From a methodological standpoint, an additional controversial issue related to the causal association between light availability for bacteria and BP is the appropriateness of measurements obtained under dark conditions.…”

Eutrophication in a tropical pond: Understanding the bacterioplankton and phytoplankton dynamics during a vibriosis outbreak using flow cytometric analyses

“…Compared to natural system, these values remain high compared to those reported by Torréton et al (2007) in the New Caledonian lagoon or by Andrade et al (2003) in a tropical eutrophic bay characterized by a significant source of allochtonous dissolved organic carbon (Table 3). Bacterial production (BP) values measured in our pond were also high, reaching 110 µg C l -1 h -1 , a threshold higher than values reported in hypertrophic ecosystems, such as polluted tropical seawaters (Sommaruga and Robarts, 1997;Bouvier et al, 2007) or urbanized area (Torréton et al, 2007). During the first 91 days, bacterial abundance was relatively stable (3x10 7 cells mL -1 ) and a positive relationship between bacterial production and picophytoplankton abundance was observed (Fig.…”

Microbial food webs in hypertrophic fishponds: Omnivorous ciliate taxa are major protistan bacterivores

“…Compared to meso-and eutrophic systems, considerably little is known about food webs in hypertrophic shallow lakes. Such systems are not only abundant but can harbor a huge diversity of rapidly growing microbes, with unique and highly complex trophic interactions (Sommaruga and Robarts 1997). In hypertrophic systems with high phytoplankton biomass and productivity (Sommaruga and Robarts 1997;Comerma et al 2003), planktonic ciliate densities can reach hundreds to thousands per milliliter (e.g., Nakano et al 1998;Šimek et al 2000).…”