Measurement of in situ clearance rates of Oikopleura vanhoeffeni (Appendicularia: Tunicata) from tail beat frequency, time spent feeding and individual body size

In situ observations (1994 to 1996) of the behavior of Oikopleura vanhoeffeni Lohmann in combination with a previously published model can be used to give a good approximation of clearance rates. The model is based on tail beat frequency, time spent feeding and subsequent measurements of individual size (trunk length). These estimated clearance rates are in close agreement with clearance rates determined in the laboratory under static and flow-through conditions. A comparison of various techniques (such as measurement of gut pigment, and various particle removal and particle uptake methods) with the behavior-model approach, revealed a convergence of all rates within a threefold range. Most of this discrepancy can be explained by the number of non-feeding individuals and the deterioration of the feeding filters in the field. The main reasons for the similarity of the various clearance rate estimates are the low variability of the behavior of appendicularians in response to environmental variables, such as temperature and particle concentration, and their non-selective retention of particles. The suggested mechanistic approach has great value for estimating the flux of material and energy through populations of appendicularians for which only size and abundance data exist, or for appendicularian species that cannot be assessed empirically. Received: 26 August 1997 / Accepted: 28 September 1998