EFFECT OF WATER CURRENTS UPON THE ATTACHMENT AND GROWTH OF BARNACLES

Abstract

The work of previous authors, dealing with the effect of water currents upon barnacle attachment, growth and distribution, is briefly reviewed. Expts. were conducted to determine the effects of water currents upon the attachment and growth of barnacles, and particularly of Balanus amphi-trite. Submerged rotating discs and glass tubes of graded cross-sectional diam. were employed to provide variations in current velocity. The velocity of water current limiting attachment appears to lie between 0.5 and 0.9 knot for Balanus amphitrite, between 0.4 and 0.7 knot for B. eburneus, and above 1.1 knots for B. improvisus. Following attachment the growth rate of barnacles was found to be increased by water currents of velocity <1.5 knots and to be decreased by currents with velocities in excess of this. The adverse effects of water currents were found to decrease with increasing age of the barnacles subsequent to attachment. 6 hrs. after attachment, growth rate was reduced to 1/3 of normal by a 1.5 knot current and completely stopped by a 3 knot current. 5 days after attachment, growth was prevented by currents ranging between 3.3 and 8 knots. Loss of attachment appeared to some extent among all barnacles in which growth rate was reduced. This loss was greatest at velocities bringing about complete cessation of growth. It is suggested that loss of attachment is due to interference with the feeding process, followed by reduction of growth rate, death, and diminished adherence. Possibly due to an orientation to the current which facilitates feeding, barnacles attached for 1 day or less show less retardation of growth rate and loss of adherence than barnacles 2 days old. Since tidal currents are almost invariably intermittent it appears from the data presented that they are not sufficient to prevent the colonization of suitable surfaces by barnacles, except where the velocities are unusually high. It also follows from the numerical results obtained that on vessels making short stays in port and relatively long voyages, little permanent barnacle fouling will occur, since those organisms which attach will be killed and at least a portion of them dislodged. The evidence does not preclude, however, the continued growth of barnacles upon slow vessels making longer stays in port, and their geographical distribution by this means.