Abstract
Sea water transport rates of the tunicate Ciona intestinalis were determined by measuring the volume of sea water transported through the specimen, and measuring the number of particles cleared by the specimen in a given time interval. The rate was also determined directly by matching the flow produced by the tunicate to that produced by a calibrated pump. Ciona transports sea water at variable rates; at times, it does not transport at all. The rate limits covering all techniques are: lower limit, 2.5 ml/hr/g wet weight and upper limit, 185 ml/hr/g wet weight; the average value based on clearance and direct measurements is 50 ml/ hr/g wet weight. Even at the lowest rate found, transport is rapid enough to ensure complete mixing between sea water and reaction or absorption sites in the pharyngeal chamber, alimentary tract or atrial chamber. We conclude that the rate controlling process for absorption of oxygen, vanadate ions, micro-organisms or organic detritus is not the rate of passage of the feeding current, but rather the rate of the intrinsic absorption process such as complex formation, ion exchange or adsorption.