PARTICLE GRAZING EFFICIENCY AND SPECIFIC GROWTH EFFICIENCY OF THE ROTIFER BRACHIONUS-PLICATILIS (MULLER)

A complete particle retention spectrum for the grazing of Brachionus p licatilis on phyto; plankton of different cell size revealed optimal g razing on an algae (Tetraselmis suecica) with an equivalent spherical diameter (ESD) of 8.3 mu m. Furthermore, although grazing sub-optimall y, the rotifer grazed with an equal efficiency (60%) on two different algae Rhodomonas baltica (R.b.) and Thalassiosira fluviatilis (T.f.) w ith equivalent spherical diameters of 6.5 mu m and 12.9 mu m, respecti vely, when they were offered one algae at a time. These two algal spec ies were in size positioned symmetrically in the bell shaped curve aro und the optimal prey size for the rotifers. In mixtures of these two a lgal species the total grazing on the two algae remained equal regardl ess of the ratio between the two species in the mixtures. The function al responses to the two algal species offered separately resulted in s imilar maximum ingestion (I-max) but different half saturation constan ts (K-m). In order to describe the growth efficiency for the rotifer, a 7 day growth experiment with the haptophyte Rhodomonas baltica was c onducted at 15 degrees C with 7 different food concentrations. The spe cific 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 r otifers vs. algal concentration also followed a Monod curve. Body leng th could be related to carbon by C-(ngC) = 1.06 x 10(-4) L-(mu m)(2.74 ). The carbon density of the rotifers were 0.11 pgC mu m(-3). The carb on yield (specific growth rate vs. specific ingestion rate) was 0.29. The maintenance food concentration was 1.02 ppm (R.b. 5000 ml(-1)). Th e rotifer lost 0.22 day(-1) when starved. The high specific growth rat e and the high saturation food concentrations as well as the high ener gy requirement during starvation supports the idea that the rotifer fo llows a life strategy with a fast growth response. (C) 1997 Elsevier S cience B.V.