Apical hair formation and growth of Fucus evanescens and F. serratus (Phaeophyceae) germlings under various nutrient and temperature regimes

Abstract

Fucoids produce numerous hyaline hairs, which are believed to assist in nutrient uptake. In this laboratory experiment, the effects of nutrient (N and P) concentrations and temperature (7°C and 17°C) on apical hair formation and growth were compared in germlings of Fucus evanescens and F. serratus, using a factorial design. Field observations indicate that F. evanescens thrives better than F. serratus in areas where nutrient levels are high and vice versa, which might result from differences in the species' autecology. In both species, germlings grew largest at 17°C, but nutrient enrichment stimulated growth only in F. evanescens germlings. The numbers and lengths of apical hairs were negatively correlated with nutrient concentration in both species and F. evanescens germlings generally developed fewer but longer apical hairs than F. serratus germlings. The negative relationship between nutrient concentration and apical hair formation increased with temperature in both species. At 17°C, the negative relationship between nutrient concentration and apical hairs was significantly stronger in F. evanescens than in F. serratus germlings, which indicates that hairs are more closely linked to nutrient uptake in F. evanescens. In a second experiment performed on 50-day-old F. evanescens germlings, transfer from high to low nutrient level for a 15-day period resulted in an increase in the number of apical hairs and their length more than doubled. Conversely, a change from low to high nutrient levels resulted in a 30% decrease in hair length. Thallus growth, on the other hand, was little affected by these changes in nutrient concentrations over the same period of time. The rapid response of hairs to changes in nutrient concentration further suggests that hairs play a significant role in nutrient uptake in F. evanescens germlings.