SENSORY ECOLOGY OF SALPS (TUNICATA, THALIACEA) - MORE QUESTIONS THAN ANSWERS

There is still relatively little known about the natural history of ge latinous animals in the plankton, and their sensory ecology remains la rgely a matter of surmise, based on limited morphological, physiologic al and behavioral data. Pelagic tunicates are among the most widely di stributed and abundant of the gelatinous zooplankton, and display a ra nge of behavior that is apparently cued by aspects of their environmen t. Different kinds of information may be important for different scale s of behavior. Feeding and predator avoidance are likely to be affecte d by near-field stimuli from visual, chemical or mechanical sources, w hile far-field information such as gravity, light, temperature, or pre ssure are likely to cue behavior spanning larger time and space scales , such as vertical or ontogenetic migration, aggregation and reproduct ive cycles. A variety of sensory structures have been described in pel agic tunicates, including photoreceptors of varying complexity, and se veral structures that have been suggested to be mechano- or chemorecep tors. Focussing on salps, this paper describes behavior that depends o n sensory information, reviews the known structure and function of sen sory receptors, and suggests some hypotheses on mechanisms defining th e sensory ecology of these planktonic organisms.