Seasonality of the red algal crust ‘Petrocelis franciscana’(Gigartinales, Rhodophyta) on boulder‐strewn shores of southern British Columbia, Canada

Abstract

SUMMARYThe red algal crust,‘Petrocelis franciscana’ Setchell et Gardner [= tetrasporophytic phase of Mastocarpus papillatus (Agardh) Kützing] exists as discrete patches on boulders throughout the intertidal zone at Burrard Inlet in Vancouver (mainland British Columbia) and at Sooke, Vancouver Island (British Columbia). This study photographically quantifies monthly surface area of 60 individual crusts over 12‐ and 18‐month periods, respectively, at the two sites. Conspicuous seasonal fluctuations in ‘Petrocelis’ abundance and relatively low survivorship of crusts sampled suggest that not all crusts are as static and as long‐lived (> 25 years) as previously suggested. Herbivory, sloughing of senescing tissue and abiotic factors visibly reduce ‘Petrocelis’ abundance in fall and winter; regeneration of lost crust tissue and relatively rapid crust growth occur from spring to early fall.