GROWTH AND LONGEVITY IN THE CRUSTOSE RED ALGA PETROCELIS-MIDDENDORFFII

Petrocelis middendorffii is a non-calcareous encrusting red alga growing on rocks in the middle and upper intertidal zone. We have photographically followed the fate of 43 individual plants for periods up to 88 months at Waadah Island, near Neah Bay, Washington (USA). Growth is slow, with surface area increasing about 4% year-1 for those individuals growing. Other plants were observed to decrease in total surface coverage, fragment, and eventually disappear. Plants on neighboring but not contiguous sample sites are not in synchrony, with some subpopulations increasing their total space coverage while others diminished theirs. Age estimates, based on a variety of growth interpretations, suggest that an average sized individual (123 cm2) will be from 25 to 87 years old. Recruitment and mortality rates appear low. The ecological traits of P. middendorffii may be similar to those of other crustose heteromorphic benthic algae. © 1979 Springer-Verlag.