Depth Maxima of Conchocelis and Phymatolithon rugulosum on the N. W. Shelf and Rockall Plateau

Conchocelis filaments in shells have been found at depths from 46 to 78 m below Chart Datum on the Malin Shelf, and the coralline red alga Phymatolithon rugulosum at 90 m on the Rockall Plateau. The use of Conchocelis growing in shells as a means of assessing the lower limits of the photic zone is restricted to coastal waters where an adequate Porphyra spore 'rain' is likely.