Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1⁻¹, the population growth constant increased from 0.17 to 0.60 d⁻¹ at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 10⁴ cells ml⁻¹, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1⁻¹ (0.3 to 1.9 individuals 1⁻¹), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod⁻¹ day⁻¹.