An Under-appreciated Component of Biodiversity in Plankton Communities: The Role of Protozoa in Lake Michigan (A Case Study)

Abstract

Recent technological advances have led to the discovery that free-living, planktonic protozoa are ubiquitous in nature and appear to be important components of pelagic food webs (e.g., fluorescent straining, flow cytometry). Despite this, limited information exists tying their seasonality to rate processes that drive succession patterns. The abundance, and seasonal growth and grazing loss of an entire protozoan assemblage were evaluated in Lake Michigan. The protozoan assemblage was species-rich (100 taxa) and abundant throughout the year in Lake Michigan. Nano-sized protozoa (Hnano and Pnano, <20 lm in size) ranged in abundance from 10 2 to 10 3 cells ml )1 , while micro-protozoa (Hmicro and Pmico, >20 and <200 lm in size) ranged in abundance from 4 to 17 cells ml )1 . The biomass of Hnano and Hmicro by itself represented more than 70-80% of crustacean zooplankton biomass, while Pnano and Pmicro constituted nearly 50% of phytoplankton biomass. Protozoa exhibited growth rates comparable to other components of the plankton in Lake Michigan, and some populations grew at rates similar to maximum rates determined in the laboratory (rates of 1-2 day )1 ). Overall, it appears that macro-zooplankton predation is a major loss factor counterbalancing growth with only small differences between the two rate processes (<0.1 day )1 ). Discrepancies between growth and grazing loss in the spring were likely attributed to sedimentation losses for larger species of tintinnids and dinoflagellates (Codonella, Tintinnidium, and Gymnodinium) that can account for their occurrence in the deep chlorophyll layer. In the summer, carnivory among similar sized species (Chromulina and small ciliates) may be additional loss factors impinging on the protozoan assemblage.

Spatial and temporal patterns of ciliate species composition (Protozoa: Ciliophora) in the plankton of the Upper Paraná River floodplain

“…However, the total number of species recorded in the present study (61 species) was higher than observed in other studies (Bossolan and Godinho, 2000;Wiackowski et al, 2001;Gomes and Godinho, 2003;Carrick, 2005;Cardoso, 2007), which registered between 17 and 36 ciliate species in plankton samples.…”

Feeding at different plankton densities alters invasive bighead carp (Hypophthalmichthys nobilis) growth and zooplankton species composition

“…Productivity in the Great Lakes is relatively low compared to the mesotrophic to eutrophic rivers, reservoirs, and backwater lakes where Asian carp commonly thrive. For example, phytoplankton biomass in Lake Michigan is typically \3 lg l -1 chlorophyll a (Carrick, 2005), whereas chlorophyll a values in the Middle Mississippi River can reach 40 lg l -1 (Williamson & Garvey, 2005). In order to predict if successful establishment of Asian carp in the Great Lakes is likely, it is necessary to determine how their feeding, growth, and survival is affected by a less productive environment.…”

Zooplankton trophic structure in Lake Michigan as revealed by stable carbon and nitrogen isotopes

“…Others have also suggested that a strong trophic link between mesozooplankton and microzooplankton exists within Lake Michigan. In particular, estimates of carbon flux from heterotrophic protozoans to mesozooplankton may rival that of phytoplankton to mesozooplankton (Carrick, 2005). Other studies using stable isotopes have also reported high trophic positions for previously described omnivore copepod species within African Lakes and have similarly suggested this may be the result of carnivory (Ngochera and Bootsma, 2010;Sarvala et al, 2003).…”

“…Gardner (2004) demonstrated that bacteria can make up a significant portion of picoplankton in Lake Michigan. Likewise, average summer biomass of phototrophic protozoans can be as high as 50% of the average phytoplankton biomass within Lake Michigan (Carrick, 2005). Finally, differences in the location of various studies within the southern basin may also explain some of the observed discrepancies.…”

“…However, some evidence has been presented that heterotrophic food sources can contribute a substantial component to the diet of Leptodiaptomus, potentially leading to the higher than expected δ 15 N (Bundy et al, 2005;Burns and Gilbert, 1993;Carrick, 2005). For example, experiments conducted with L. sicilis taken from Lake Michigan found that they may selectively feed on microzooplankton, which can make up 22% to 74% of their total ingested carbon (Bundy et al, 2005).…”