A cultural assessment of the distribution of Callithamnion hookeri (Dillw.) S. F. Gray (Rhodophyta, Ceramiales) in nature

Abstract

The life history of C. hookeri was demonstrated on the basis of culture to be of the ‘Polysiphonia-type’. Isolates from N.E. Scotland and S.W. England were interfertile in culture. The absence of the species from estuaries correlated with its relatively stenohaline nature in culture. The geographical distribution correlated with the August mean surface water isotherms at both its northern (about 10°C) and southern (about 22°C) limits of occurrence, the former being the minimum temperature and the latter the maximum temperature at which growth proceeded in culture, respectively. The occurrence of the alga in shaded locations on the shore correlated with the ability of the species to grow in culture at extremely low light intensities. There was no marked stimulation of growth on removing small amounts (2–4%) of green light, which suggests that Boney's hypothesis that the phycobilins of intertidal red algae function in the removal (absorption?) of harmful green light, does not apply to this species. The seasonal growth appears to be temperature controlled, based on cultural studies.