Simultaneous measurement of food particle selection and clearance rates of planktonic oligotrich ciliates (Ciliophora:Oligotrichina)

Abstract

Ohgotrich ciliates are a major microzooplankton component in the northern Baltic Sea during summer The use of wheat starch particles as a tracer-level food source enabled us to simultaneously evaluate in situ clearance rates and food particle size selection of natural ciliate assemblages. Average clearance rates of 9 ciliates of the genera Lohmanniella, Strobilidium, Strombidium, Tintinnidium and Tintinnopsis on their most favored particle sizes ranged from 1.9 to 11.4 p1 cell-' h-'. Particle size selectivity was studied by the use of x2-based selectivity index. Each species showed a specific particle size preference pattern. The optimal particle size varied from 1.4 pm (Strombidium sp. 20 pm in size) to 9.8 pm (Strobilidium sp. 40 pm). Most species were able to ingest effectively nanoflagellate-size food, but only 2 of the species showed effective grazing on the smallest particles, suggesting a possible ability to utilize bacteria-size prey. The overall ciliate food size spectrum covered the size range of the most abundant food items in the Baltic summer plankton. Among the ciliates investigated, there appears to be 2 different feeding strategies: specialistic and generalistic, where the ciliates either concentrate on feeding on a narrow size range of food organisms, or use food particles of a wide size range, with little or no preferences within this range.

Spring bloom succession, grazing impact and herbivore selectivity of ciliate communities in response to winter warming

“…As proposed by Montagnes et al (1988), clear spring assemblages with large-sized ciliates preying upon large phytoplankton size fractions are found, while summer, autumn and winter assemblages are usually dominated by small ciliates consuming small prey, e.g., bacterioplankton and flagellates (Kivi and Setaelae 1995;Setaelae and Kivi 2003). Our findings of composition changes and shifts towards larger ciliate size fractions during spring support Montagnes and coworkers' general concept on ciliate seasonal succession, a pattern which is additionally confirmed by field observations during spring succession in the Baltic Sea (Smetacek 1981;Johansson et al 2004).…”

“…Traditionally, ciliates were considered as major grazers of microalgae, preying mainly upon nanoplankton size fractions (Jonsson 1986;Kivi and Setaelae 1995;Grané li and Turner 2002;Sommer et al 2005;Berninger and Wickham 2005), whereas large phytoplankton size fractions like, e.g., diatoms are usually considered as the preferred food item of copepods (Kivi et al 1996;Grané li and Turner 2002;Sommer et al 2005). In addition, recent studies also point to the ciliates' importance as bacterivores and to their role as a trophic link between the microbial components in the food web and higher trophic levels (Posch et al 1999;Simek et al 2000).…”

Dinoflagellates and ciliates at Helgoland Roads, North Sea

“…As they can respond more quickly to increasing phytoplankton concentrations, ciliates play a key role during spring (Riegman et al 1993) and form an earlier peak than dinoflagellates. The majority of ciliates is, with few exceptions (Smetacek 1981;Aberle et al 2007), restricted to the availability of smaller prey (Jonsson 1986;Tillmann 2004) consisting mainly of flagellates (Kivi and Setälä 1995), and their seasonal co-occurrence can be linked to that fact. Heterotrophic dinoflagellates are generally directly related to the availability of larger phytoplankton prey (Hansen 1991) and often occur at high concentrations during the course of diatom blooms (Sherr and Sherr 2007) especially during spring blooms (Stelfox-Widdicombe et al 2004).…”

Conserving original in situ diversity in microzooplankton grazing set-ups

“…The taxa Lohmanniella and M. rubra are widely distributed in coastal and open ocean environments (Smetacek, 1984;Kivi & Setälä, 1995;Myung et al, 2006;Park et al, 2007) and are also important members of the microzooplankton community in the North Sea around Helgoland (Figure 4). Both are known to feed on nanoplankton (Jonsson, 1986;Christaki et al, 1998;Aberle et al, 2007;Park et al, 2007) and bacteria (Myung et al, 2006).…”

“…As the importance of microzooplankton as fundamental grazers in planktonic food webs became recognized, diverse techniques for determining the grazing impact of microzooplankters were developed (Kivi & Setälä, 1995). The most widely used method to estimate in situ grazing rates is Landry & Hassett's dilution technique (Landry & Hassett, 1982;Calbet & Landry, 2004) which facilitates the estimation of grazing rates in barely manipulated grazer communities.…”