Predator deterrence and 2,4-dibromophenol conservation by the enteropneusts Saccoglossus bromophenolosus and Protoglossus graveolens

Saccoglossus bromophenolosus King et al., 1994 and Protoglossus graveolens Giray & King, 1996 contain high concentrations of 2,4-dibromophenol (DBP), the function of which is uncertain. Mature enteropneusts that were collected from the field and maintained in vitro without bromide retained DBP, which is inconsistent with active DBP secretion info the burrow environment. DBP was also conserved during field manipulations that decreased food availability in situ. Further, DBP did not deter predation in feeding experiments with the anomuran crab Pagurus longicarpus and the polychaetes Glycera dibranchiata, Nereis virens and Nephtys incisa. The hermit crabs fed on S. bromophenolosus readily, and in preference to shrimp, in the field and in laboratory aquaria. Elevated DBP levels were measured in crabs that had recently consumed S. bromophenolosus, and ingested DBP was degraded to 4-bromophenol. Elevated levels of DBP in polychaetes were associated with the disappearance of enteropneusts during in vitro feeding experiments. Control incubations with DBP-containing agar plugs indicated that the polychaetes did not accumulate DBP passively. These results suggest that DBP is not an effective anti-predatory agent against hermit crabs or some predatory polychaetes. A definitive role for DBP in enteropneusts remains to be shown.