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. Calycophorae
and Physonectae showed a two-phase cycle of fishing and swimming.
The fishing posture of a siphonophore is determined by its floatation
and by the contractility of its stem; fishing postures can be similar in siphonophores which are unrelated generically. Total tentacle
length in colonies with 2 - 3 mg body protein can extend 4.5 meters.
Variations in the morphology of tentilla reflect differences
in the kinds of prey which can be captured. Dissection of feeding
polyps revealed that most siphonophores could eat copepods, amphipods,
polyc:haetes, 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. Since a single feeding
polyp of species which captured nauplii could ingest more than one
per minute, colonies with 20 - 150 feeding polyps may be able to eat
several hundred individuals within minutes if they encounter aggregations
of small zooplankton.
Agalma okeni was the most common siphonophore encountered by
divers. Colonies of A. okeni maintained in the laboratory on a diet
of Artemia nauplii, copepods, or shrimp budded an additional feeding
polyp and 1 - 2 pairs of nectophores about every two days. Energetic
calculations suggest that small and medium-size colonies incorporate
48% and 33%, respectively, of ingestion into production. A small
colony of A. okeni with six nectophores probably requires 2.8 - 5.0
calories to balance daily rates of oxygen consumption and growth; a
medium-size colony with 14 nectophores probably requires 5.8 - 9.2
calories. Extrapolating from short-term increases in size in the
laboratory, the generation time of A. okeni in tropical and subtropical
regions is likely 2 1/2 - 4 weeks.
Respiration of siphonophores at 26 ± 3°C ranged from 2 - 86 μ1 02/mg protein-hr, and ammonia excretion ranged from 0.1 - 3.3 μg NH4/mg protein-hr. The cystonects Rhizophysa filiformis and Bathyphysa sibogae had low rates of respiration and excretion,
while calycophores of the genus Sulculeolaria had the highest rates.
For most siphonophores, ratios of oxygen consumed to ammonia-nitrogen
excreted ranged from 16 - 36 and suggest that both protein and lipid
are important metabolites.
