Efficiency of Particle Retention and Filtration Rate in Four Species of Ascidians

Particle retention in Ascidiella aspersa, Molgula manhattensis, Clavelina lepadiformis and Ciona intestinalis was determined from comparisons of particle-size distributions in the inhaled and exhaled water. Particles down to 2-3 jun were completely retained and the retention efficiency of smaller particles decreased to about 70 "/o for 1 ~u n particles. There was no indication that the ascidians were able to adjust their retention efficiency. Filtration rates (F, m1 min-l) as a function of total dry weight (W,,,,,, g) could be expressed as F = 54.4 W,0,,,'-05 in A. aspersa and F = 46.4 Wr0r,P-84 in C. intestinalis. It is concluded that undisturbed ascidians filter the water continuously at constant rates.