Differential meiospore size and tolerance of ultraviolet light stress within and among kelp species along a depth gradient

Kelp are differentially stratified along a gradient of UV exposure (as a fu nction of water depth). The role of ultraviolet light in seaweed zonation h as not been fully explored. This study found a significant meiospore size d ifference within and among the kelp species examined: Pterygophora californ ica Ruprecht (high to mid-subtidal), Laminaria groenlandica Bory (high to m id-subtidal), Laminaria groenlandica Rosenvinge (high-subtidal), Alaria mar ginata Postels and Ruprecht (low-intertidal) and Hedophyllum sessile Setche ll (mid-intertidal). This size difference was correlated with the depth dis tribution of adult plants, with the largest meiospores originating from sha llow-dwelling adult kelp exposed to high UV light. Under UV stress in the l aboratory, meiospores from adults growing in high-UV environments displayed greater germination and survival rates than the progeny of adult kelp occu pying lower-UV environments. This suggested that in Barkley Sound, British Columbia, Canada, differential tolerance to UV (possibly determined by meio spore size) may limit the upper settlement position of kelp species and ind ividuals. Tolerance to UV may be an important determinant of kelp zonation on rocky shores.