The Portuguese Man-of-War, Physalia Physalis L., in British and Adjacent Seas

Abstract

The occurrence in the summer of 1945 of a swarm of Physalia physalis L. off the south-west coast of the British Isles has initiated a survey into records of its appearance on the Atlantic coasts of Europe during the past 100 years. Unpublished records for 1912, 1913, 1934 and 1935 were discovered and are listed with those already known. The 1945 strandings are considered in detail in conjunction with meteorological data for the period involved. It is concluded that winds, rather than water movements, are the main factor in transporting the swarms towards the British Isles and it is considered likely that the swarms come from the Azores-mid-Atlantic region rather than from the Canaries-Gibraltar district.Associated with the Physalia were Lepas fascicularis and L. pectinata, some Velella, a few turtles (Caretta caretta), and possibly an Opah fish (Lampris luna), all of them, with some reservation respecting the last-named, surface organisms that would come under the same meteorological influences as the Physalia.A living specimen of Physalia gave an opportunity to observe the method of feeding of which few previous first-hand accounts exist. The capture of the prey by the dactylozooids and its subsequent digestion by the gastrozooids is illustrated by photographs from life and is described in some detail. It is suggested that the rolling of the pneumatophore from side to side, dipping the crest in the water, is a calm-weather habit directed to keeping moist the upper surface exposed to the air.