Particle grazing efficiency and specific growth efficiency of the rotifer Brachionus plicatilis (Muller)

A complete particle retention spectrum for the grazing of Brachionus plicatilis on phytoplankton of different cell size revealed optimal grazing on an algae (Tetraselmis suecica) with an equivalent spherical diameter (ESD) of 8.3 μm. Furthermore, although grazing sub-optimally, the rotifer grazed with an equal efficiency (60%) on two different algae Rhodomonas baltica (R.b.) and Thalassiosira fluviatilis (T.f.) with equivalent spherical diameters of 6.5 μm and 12.9 μm, respectively, when they were offered one algae at a time. These two algal species were in size positioned symmetrically in the bell shaped curve around the optimal prey size for the rotifers. In mixtures of these two algal species the total grazing on the two algae remained equal regardless of the ratio between the two species in the mixtures. The functional responses to the two algal species offered separately resulted in similar maximum ingestion (I(max)) but different half saturation constants (K(m)). In order to describe the growth efficiency for the rotifer, a 7 day growth experiment with the haptophyte Rhodomonas baltica was conducted at 15°C with 7 different food concentrations. The specific growth rate vs. food availability followed Monod kinetics with a maximum specific growth rate (G(max)) = 0.49 day^-1 and a K(m) = 2.25 ppm (R.b. 12 150 ml^-1). The mean carbon content of the individual rotifers vs. algal concentration also followed a Monod curve. Body length could be related to carbon by C((ngC)) = 1.06 x 10^-4 L((μm))/²⁷⁴. The carbon density of the rotifers were 0.11 pgC μm^-1. The carbon yield (specific growth rate vs. specific ingestion rate) was 0.29. The maintenance food concentration was 1.02 ppm (R.b. 5000 ml^-1). The rotifer lost 0.22 day^-1 when starved. The high specific growth tale and the high saturation food concentrations as well as the high energy requirement during starvation supports the idea that the rotifer follows a life strategy with a fast growth response.