Growth rates, standing stocks, and estimates of net primary production for the kelps <i>Agarum clathratum</i>, <i>Hedophyllum nigripes</i>, and <i>Eualaria fistulosa</i> (Phaeophyceae, Laminariales) in Kachemak Bay, Cook Inlet, Alaska

Abstract We measured baseline growth rates of perennial understory kelps, Agarum clathratum and Hedophyllum nigripes , and canopy-forming Eualaria fistulosa from March 1977 through October 1978 in Jakolof Bay, Kachemak Bay, Alaska. We measured density and biomass of several kelp species in the entrance to Jakolof Bay, at Seldovia Point, and at Latouche Point, Latouche Is., in an ocean entrance into Prince William Sound. We used Kachemak Bay data to estimate primary productivity in these kelp beds. In view of current records demonstrating increasing sea-surface temperatures in the Gulf of Alaska, these baseline data provide a useful basis for evaluating effects of climate change or other environmental effects. Growth rates, highest from late winter/early spring and lowest from late summer until mid-winter, changed seasonally. Rates were fastest in Eualaria , the largest of these kelps, and slowest in Agarum , the smallest. Rates and seasonality of stipe growth varied among species. Stipe growth, observed seasonally in Agarum and Hedophyllum , occurred from spring through mid-summer; rates were slowest in Agarum . Stipe growth in the annual Eualaria occurred throughout its life span. Tissue growth and primary production varied among species; all produced appreciable quantities of fixed carbon annually. Estimated production for understory kelps off Seldovia Point varied from 73 g C m −2 yr −1 for Agarum to 87 g C m −2 yr −1 for Hedophyllum . Estimated production for canopy-forming kelps was an order of magnitude higher. Value of these decades-old baseline data cannot be over-emphasized in view of growing awareness of effects of climate change on kelps.