Apical elongation of fucoid algae exposed to low salinities

Abstract

Apical elonggation of five intertidal fucoids ( Pelvetia canaliculata (L.) Dec. et Thur., Ascophyllum nodosum (L.) Le Jol., Fucus spiralis L., Fucus vesiculus L. and Fucus serratus L.) was measured during exposure to different salinities. The response could be separated into two distinct phases, an initial (0–3 h) very rapid elongation due to osmotic effects, and after about 24 h an approximately steady state where elongation rates probably represented normal growth rates. Elongation rates during the initial phase were inversely correlated to salinity. In the steady state phases, all species demonstrated a very wide salinity tolerance for elongation rate. For P. canaliculata, the maximum elongation rate was observed at the lowest salinity applied, 2.6%. Cumulative elongation including both phases showed a maximum at salinities less than 20 0 00 , and exposure to a variable salinity regime ( 34 sol;0 00 for 23 h, 5 0 00 for 1 h) for 5 days showed stable elongation rates after 2 days of exposure, 2–3 times higher than at 34 0 00 . This indicates that exposure to low or variable salinities increases total elongation, and it is suggested that this may enhance competition for light and thus be of ecological significance.