Depth distribution of endolithic algae from the Firth of Clyde: implications for delineation and subdivision of the photic zone

Abstract

INTRODUCTIONSome marine endolithic algae grow well and are restricted to the strongly lit littoral and uppermost sublittoral environments. The wide depth ranging boring algae must however adapt to different light intensities. Whereas Eugomontia sacculata Kornmann is considered as a form adapted to high light intensity (Akpan, 1981), Ostreobium quekettii Bornet & Flahault and Conchocelis - a boring phase in the life cycle of red algae in the Porphyra and Bangia genera - are able to survive under low light conditions even though they thrive at depths with strong illuminations (Rooney & Perkins, 1972; Clokie & Boney, 1980). Sheath, Hellebust & Sawa (1977) have demonstrated that the Conchocelis of a Porphyra sp. can survive prolonged very dim light condition and probably remain in a ‘steady state’ without growth in the dark for a long time. This adaptation is important for those algae in the lower part of the photic zone because during winter, deep light penetration is hampered.