The Effects on Intertidal Fucoid Algae of Exposure to Air under Various Conditions

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Abstract
Pelvetia canaliculata and Fucus spiralis plants were exposed to air at different temperatures and water potentials, then resubmerged in seawater and observed in culture. Drought injury was manifested as an initial decrease in fresh weight followed by the appearance of dead, discolored spots on the thallus, damage to growing apices and temporary curtailment of growth. Plants subsequently recovered except when injury was extreme. Damage was greater at 25.degree. C than at 9.degree. C and increased with duration of exposure. At 25.degree. C, partial dehydration (-100 to -395 bars water potential) was more harmful than desiccation to -1375 bars; hence rapid tissue water loss during tidal exposure is advantageous to these algae. Simulated rainfall caused little injury even at 25.degree. C. However, fresh water sprayed on air-dry plants accentuated the effects of dehydration. Results are discussed in relation to an earlier field study which showed that intertidal fucoid algae are most critically affected by prolonged emersions during warm weather.