Factors Influencing Growth-Rate in Balanus balanoides

Abstract

Barnacles parasitized by Hemioniscus balani grew more slowly than unparasitized individuals. The passage of an uninterrupted current of water over the barnacles was the most important factor in promoting rapid growth. Population density appreciably influenced growth in volume only when the individuals were closely packed, either touching or nearly touching. Even at densities as high as 4 individuals/cm2 much of the loss in cross-sectional area caused by space limitation was compensated for by increase in height. The effect of close packing in itself did not appear to be harmful. In a unidirectional current, there was little evidence that the leading individuals in a group grew appreciably faster than the trailing ones. Orientation with the rostrum pointing to the current source conferred an advantage resulting in slightly enhanced growth. It is shown that a barnacle whose growth is isometric and determined only by the rate of intake of food from a current of constant nutrient content would grow at a constant linear rate. This is approximately true for the greater part of the growth curve of the species investigated. Early growth just after metamorphosis is slower, probably because the rate of water flow is reduced in the immediate vicinity of the solid substratum. Growth slows down after maturity in all species as a consequence of metabolic changes.