Factors Influencing Growth-Rate in Balanus balanoides

The rate of growth of the common shore barnacle of boreal coasts, Balanus balanoides (L.), has been investigated at a number of localities by different workers. The literature has been critically reviewed by Barnes & Powell (1953), who concluded that the seasonal changes in rate of growth were similar over the whole of its range. Nevertheless, the actual rates of growth vary considerably as can be seen from the summary of earlier work given in Table 1, in which growthrates are compared on the basis of size attained at the end of the first year. Only a limited study has been made of the factors controlling growth in any one given area. The influence of the tidal level at which the barnacle grows has been shown by Hatton & Fischer-Piette (1932), by Moore (1934) and by Barnes & Powell (1953) to be of importance, those individuals able to feed for a longer period at the level of low water growing faster than those living at high water. Bames (1953) investigated growth-rates at different light intensities, and concluded, notwithstanding the observations of Klugh & Newcombe (1935), that light was without influence. In further measurements on specimens immersed continuously from a raft, Barnes (1955) found that the presence of competing organisms seriously interfered with growth especially in its early stages soon after settlement. Hatton & Fischer-Piette (1932) compared growth-rates at stations in the same locality differing in their exposure to wave action, and found that growth was greatest at exposed localities, a conclusion also reached by Moore (1934) in the Isle of Man. Moore (1936) found that, at localities near Plymouth, growth was greater where there was a current of water containing suspended matter than at more exposed localities with clear water in the same area; Hatton (1938) demonstrated the advantage of water flow in the St Malo area by transplanting individuals on rock from a stagnant area to one where they were in the path of tidal currents. Moore (1934, 1958) found some evidence that crowded individuals grew more slowly, but his findings may be criticized on two grounds; first that one of the isolated individuals with which the crowded ones were compared could clearly be seen in the original plate to be Chthamalus stellatus, secondly because the crowded group had settled in a shallow groove which, as Hatton (1938) later demonstrated, would itself retard growth. It is convenient to divide the factors influencing growth-rate into two groups, regional and local. Regional environmental factors include the temperature and salinity of the water and its richness in suspended nutrients, while lccal environmental factors include the flow of water over the barnacle, the orientation of the