Field studies of fishing, feeding, and digestion in siphonophores†

Abstract

The feeding and fishing behavior of siphonophores in their natural environment was observed by SCUBA diving at 171 stations in warm‐water areas of the western North Atlantic Ocean. The fishing posture of a siphonophore is determined by its flotation and by the contractility of its stem; fishing postures can be similar in siphonophores which are unrelated generically. Tentacle length in colonies with 2–3 mg body protein can total 4.5 meters. Variations in the morphology of tentacles reflect differences in the kinds of prey which can be captured. Dissection of feeding polyps revealed that most siphonophores could eat copepods, amphipods, polychaetes, pteropods, heteropods, veliger larvae, sergestids, mysids, euphausiids, and small fish, though laboratory experiments showed that not all could eat nauplii. Species which could capture Artemia nauplii usually required 2–4 hours to digest them, while large prey took 7–18 hours to be digested. By extrapolating from laboratory feeding experiments with small siphonophores it is suggested that colonies with 50–150 feeding polyps could eat several hundred individuals within minutes if they encountered aggregations of small Zooplankton.