The effect of depth on summer growth of Laminaria saccharina (Phaeophyta, Laminariales)

Mature Laminaria saccharina sporophytes transplanted to seven depths between 1 and 21 m below mean low water showed different rates of blade growth during July. A maximum rate of 1·15 cm day−1 occurred at 9 m. Elongation proceeded about 40% as rapidly in transplants at 1 and 3 m and in undisturbed plants on shore at 0 m. Growth was much reduced below 17 m. Low levels of nitrate and high temperatures near the surface and attenuated illumination at depth are suggested as limiting factors. A quantitative survey of subtidal kelp beds around the study site showed that L. saccharina dominates L. digitaca and Agarum cribrosum in abundance and biomass between 2 and 8 m.