Plankton food web structure in a eutrophic polymictic lake with a history of toxic cyanobacterial blooms

Abstract

We studied the seasonal dynamics of phytoplankton, bacterioplankton, heterotrophic nanoflagellates, ciliates, and metazoan plankton in the highly eutrophic polymictic Lake Kastoria (Greece), which has a history of toxic cyanobacterial blooms. An acute increase in the flushing rate of the lake during spring inhibited cyanobacterial biomass accumulation. During this transient oligotrophic period, which was characterized by abundant lake snow particles, the plankton food web was an inverted biomass pyramid (low autotrophic biomass and high heterotrophic biomass). Prokaryotes played a key role in these changes (cyanobacteria during periods of autotrophy and bacteria during periods of heterotrophy). In summer and autumn, toxic cyanobacterial blooms developed, and the microbial loop was weak. The microbial loop was weak because the heterotrophic nanoflagellates and nanociliates decreased to undetectable densities during the summer, when larger bacterivores (rotifers and small cladocera) were abundant. Toxic blooms may have a dual effect on heterotrophic nanoplankton: negative during the first bloom and postbloom period and positive during a following toxic bloom. Different species (Cylindrospermopsis raciborskii, Aphanizomenon spp., and Microcystis aeruginosa) and succession phases of toxic blooms may differentially affect the microbial food web structure.In pelagic systems, phytoplankton and bacterioplankton constitute the complementary functional components that primarily produce new particulate matter by autotrophy and heterotrophy. Their carbon pool represents the base of grazing food chains and the microbial loop. Thus, the relative dominance of each functional component has significant implications for food web structure and the function and bio- AcknowledgmentsWe would like to thank the two anonymous reviewers and Associate Editor R. Bachmann for their constructive criticisms and suggestions. We are grateful to U. Sommer for his critical comments and suggestions on drafts of this manuscript and to U. Christaki for her helpful comments. We thank L. Economou for linguistic suggestions and C. M. Cook for the critical reading of sections of the manuscript concerning cyanotoxins. This work was partially funded by the Municipality of Kastoria, Research Committee, Aristotle University of Thessaloniki, project 7468. We thank all participating members of this project.

Modelling ecosystem structure and trophic interactions in a typical cyanobacterial bloom-dominated shallow Lake Dianchi, China

“…In Dianchi Lake, MC-containing and MC-free strains usually coexisted, but largesized Microcystis (over 100 m) accounting for approximately 80% of the total biomass (unpublished data) could account for the potentially high concentration of MCs (Wang et al, 2013). The zooplankton structure accompanied by cyanobacterial blooms in Lake Dianchi was in line with the findings of Hansson et al (2007) and Moustaka-Gouni et al (2006). Toxic cyanobacteria were shown to be negatively correlated with large unselective herbivores such as Daphnia and calanoid copepods, whereas they were positively correlated with small, relatively inefficient phytoplankton feeders such as cyclopoid copepods, bosmina, and rotifers.…”

Indirect effect of environmental factors on interactions between microbial and classical food webs in freshwater ecosystems

“…Correlation analyses showed that in the studied lakes, links between microbial and classical food webs occurred at each level of the microbial loop. Evidence for the cascading effect of crustaceans on bacteria mainly came from meso-and microcosm experiments, but the effect of crustaceans on bacteria in natural conditions was also proved (Moustaka-Gouni and Vardaka, 2006). It is generally considered that crustacean plankton affect the whole microbial food web, i.e., from ciliates to larger bacteria (Ju¨rgens and Stolpe, 1995).…”

The trophic role and impact of plankton ciliates in the microbial web structure of a tropical polymictic lake dominated by filamentous cyanobacteria

“…However, a careful follow-up of the nanociliate and picoplankton densities for several days would be necessary to determine if top-down control actually prevails or if the observed pattern observed was a result of picoplankton depletion by nanociliates. The ciliate biomass did not appear to be affected by the filamentous cyanobacteria density, which is inconsistent with what was found for a lake with toxic cyanobacterial blooms, where Cylindrospermopsis raciborskii (but not Microcystis aeruginosa) blooms depressed both the nanoflagellate and nanociliate assemblages (Moustaka-Gouni et al, 2006).The biomass distribution by morphotype differed between the surface and bottom samples despite the mixed character of the water column, and this result may be indicative of a patchy distribution (Fig. 4).…”

“…Moreover, the ciliate importance to the food web increases with higher primary productivity (Sherr and Sherr, 2002), although it remains to be shown if this relationship holds true for tropical lakes, such as Catemaco. The nature of lacustrine trophic microbial web components and their interactions have been studied for temperate lakes with different trophic statuses (Straškrabová et al, 1999;Pfister et al, 2002;Auer et al, 2004;Chróst et al, 2009;Agasild et al, 2013;Van Wichelen et al, 2013), including eutrophic temperate lakes affected by cyanobacterial blooms (Moustaka-Gouni et al, 2006;Zingel et al, 2007;Zingel and Nõges, 2010), shallow soda lakes of Africa (Burian et al, 2013), relatively shallow eutrophic lakes, deep oligotrophic tropical lakes of Eastern Africa (Yasindi and Taylor, 2003), deep athalassohaline lakes of North America Peštová et al, 2008), and shallow subtropical lakes with differing trophic statuses (Beaver and Crisman, 1989;Beaver and Crisman, 1990;Gomes and Godinho, 2003;MachadoVelho et al, 2005;Havens et al, 2007;Bagatini et al, 2013;Machado-Velho et al, 2013). These studies have demonstrated that microbial food webs, particularly the composition, abundance, biomass and diversity of ciliates, present specific responses to the geographic, climatic and ecological features of different lakes and reservoirs.…”