A SEASONAL COMPARISON OF CARBON, NITROGEN, AND PIGMENT CONTENT IN LAMINARIA-SOLIDUNGULA AND L-SACCHARINA (PHAEOPHYTA) IN THE ALASKAN ARCTIC

Laminaria solidungula and L. saccharina inhabit the Beaufort Sea in th e Alaskan High Arctic. Laminaria solidungula is an Arctic endemic, whe reas L. saccharina extends from north temperate Pacific and Atlantic w aters to the Arctic. Previous studies have shown that the two species have different seasonal timing of growth, but little comparative physi ological information exists. As a first step in characterizing these t wo species from a mixed Arctic population, we measured variations in c arbon, nitrogen, and photosynthetic pigment content in blade tissue fr om plants collected under the fast ice in April and during the open wa ter period in late July. Both species exhibited seasonal differences i n many measured variables; seasonal differences in L. solidungula were mast pronounced in growing basal blades. For example, the molar C/N r atio of basal blades averaged 11 in April and 21 in July for L. solidu ngula and 11.5 in April and 28 in July for L. saccharina. Basal and ma ture second blades differed in pigment content in April but not in Jul y: chlorophyll a + c in L. solidungula basal and nature second blades averaged 19 and 27 nmol . cm(-2) in April and 30 and 29 nmol . cm(-2) in July, respectively. The corresponding values for L. saccharina were 17 and 29 nmol . cm(-2) in April and 16 and 1G nmol . cm(-2) in July (95% confidence intervals approximately 1-3 nmol . cm(-2)). Carotenoid s exhibited similar patterns. Species differences in pigments, carbon, and nitrogen were minor and were probably effects rather than causes of the different seasonal patterns of growth and development. The prim ary difference between the two species may be the ability of L. solidu ngula to retain multiple metabolically active blades and to fuel areal growth with stored carbohydrates during winter near darkness, whereas L., saccharina growth is more closely tied to active photosynthesis i n the growing basal blade. The cause of old blade retention in L. soli dungula and the possibility of other physiological differences between the two species, including gametophytes, remain to be determined.