We examined the growth, productivity, and turnover of sublittoral fringe populations of Laminaria longicruris in high- and low-flow habitats (headlands and bays, respectively) in Cobscook Bay during 1995 and 1996. We used the hole-punch technique, incorporating increases in length and width (area) to estimate frond growth. Regression analysis was used to predict biomass from frond area. Water temperature, salinity, and nutrients were measured monthly. Kelp tissue was analyzed to assess nutrient-growth relationships. Mean ± SD monthly productivity at Bar Island (low-flow) ranged from 0.42 ± 0.31 to 8.61 ± 2.37 g dry m⁻² day⁻¹. Productivity estimates for Mahar Point and Garnet Point (headlands) exhibited a lower and narrower range of values, 0.25 (n = 1) to 3.67 ± 0.79 g dry m⁻² day⁻¹ and 0.46 (n = 1) to 5.82 ± 2.27 g dry m⁻² day⁻¹, respectively. The overall range of productivity estimates based on carbon was 0.08 (n = 1) to 2.58 ± 0.71 g C m⁻² day⁻¹. Growth in these fringe stands was comparable to kelps in general, but productivity was slightly lower, likely due to lower stand densities and, possibly, stress from aerial emergence during low tides. We estimated that 75 hectares of the Bay was in L. longicruris production yielding 3.34 × 10⁷ g C year⁻¹.