Growth dynamics of Saccharina latissima (Laminariales, Phaeophyceae) in Aarhus Bay, Denmark, and along the species' distribution range

Growth dynamics of Saccharina latissima in a Danish embayment (56A degrees 03.793N, 10A degrees 16.148E) were investigated through an annual cycle (March 1999-March 2000) and related to patterns found in previous studies covering the distribution range of the species. The kelps exhibited meristematic growth as well as distal tissue loss all year around. Elongation rate peaked in spring (March-May, 0.75 cm day(-1)), whereas maximum biomass growth occurred in May-July at higher insolation. S. latissima accumulated nitrogen (N) in November-March, when ambient N levels were high and the fast growth in March-July was followed by a depletion of these reserves. Light regimes and seasonal fluctuations of nutrients were, thus, major factors explaining the seasonal growth pattern of S. latissima in this temperate bay. Differences in light and exposure along depth gradients affected the growth, loss and storage product dynamics. High losses of N and carbon (C) through summer abscission of distal tissue question the efficiency of translocation, especially at shallower depths, where losses are accelerated by, e.g., high temperature. A large-scale comparison further highlighted that warming advanced the timing, increased the level of peak growth and also seemed to expand the growth period. Growth rates of the studied Danish population fell in the low end of the range for similar latitudes and temperatures, probably due to sub-optimal salinities (avg. 23.3 psu) in combination with periodically high summer temperatures (max. 21.1 A degrees C).