Interaction between the Plasma of the Loggerhead Turtle and Toxin of the Portuguese Man-of-War

Abstract

THE loggerhead turtle, Caretta caretta, is reported to eat the Portuguese man-of-war, Physalia physalis ^1–3. Where Physalia are assembled in windrows, loggerheads are often seen at the surface with eyes closed, eating this siphonophore. Velella, an allied species, has also been identified from stomach contents of a turtle which was identified as a loggerhead⁴. Physalia is equipped with a singularly potent toxin⁵. This is contained in nematocysts which can penetrate a rubber glove and presumably even the chitinous exoskeleton of a crab's leg. As Barbour pointed out, the dense impenetrable skin of the face and jaws might protect a turtle from some of the obvious hazards of such a feast. However, since tentacles of active colonies have been observed to cling tightly to the skin, gloves, glass containers and even to the polished steel surface of a pair of scissors, it is difficult to explain the ability of the turtle to swallow, much less to digest and survive this meal. We believe that the acid of the stomach contents would inactivate the nematocyst and its contained venom virtually upon contact. The unconcern of the adult turtle with the toxic effects of the nematocysts might be due to the presence of protective antibodies in the blood acquired by contact with Physalia early in life. It is the object of this communication to report the results of experiments designed to test this hypothesis.