Effect of food density of Pseudokirchneriella subcapitata and Chlorella vulgaris on the population growth rates of four brachionid rotifers

We conducted population growth experiments for 2–4 weeks using 4 species of brachionid rotifers (Brachionus angularis, B. havanaensis, B. rubens, and Plationus patulus), all isolated from Lake Xochimilco, Mexico City, Mexico. The test rotifers were fed 2 species of green algae (Chlorella vulgaris and Pseudokirchneriella subcapitata) at 3 food concentrations (2.9, 5.8, and 11.6 µg dry weight mL−1) for 24 h. Regardless of algal species, the population density of all 4 rotifer species increased with increasing food density; however, the magnitude of growth rate response of the rotifers differed. At comparable food levels, B. havanaensis had far greater abundances in 3 weeks than the other 3 rotifer species. At a concentration of 2.9 µg mL−1 of C. vulgaris, density of B. angularis was about 50 ind. mL−1, but when the food was enhanced to 11.6 µg mL−1, its population was 3 times higher; similar values were obtained when B. angularis was fed P. subcapitata. In comparison, B. havanaensis fed P. subcapitata at the highest food level had population abundances of about 900 ind. mL−1; at the same food level, when fed C. vulgaris, the density was much lower (250 ind. mL−1). Population abundances of B. rubens fed P. subcapitata were, in general, lower than those fed C. vulgaris. This was also the trend for rotifer P. patulus, which had lower abundances when fed P. subcapitata than when fed C. vulgaris. Regardless of food type and concentration, the rate of population increase per day (r) of the tested rotifer species varied from 0.16 to 0.61 d−1