Growth Strategies of Three Laminaria Species (Phaeophyceae) Inhabiting Different Depth Zones in the Sublittoral Region of Helgoland (North Sea)

Abstract

ABSTRACT. On European coasts, Laminaria digitata does not inhabit the deeper kelp zone; this is dominated by L. hyperborea and (locally) L, saccharina. Sporophytes of three Laminaria spp. were cultivated from unialgal gametophyte cultures in the laboratory and transplanted into the field in February, at depths of 2,4.5 or 7 m below M.L.W.S. Near Helgoland, the deepest kelp (L, hyperborea) occurs at 8 m, and older plants of L. digitata are not found below 2 m depth. Photosynthesis was light-saturated in all three species, irrespective of cultivat.ion depth, at photon flux densities above about 150 pE m-2s-1 (corresponding to an irradiance of 30 W m-2). The experimental plants of L. digitata and L. saccharina produced much bigger blade areas in spring and summer at all depths than L. hyperborea. In July, the latter species completely ceased blade growth and L. saccharina reduced its growth rate very much. L. digitata, however, first reduced its growth rate in September (by about 50 */D), so that at the beginning of the dark season, from October onwards, its blades consisted of much younger tissue, resulting in a lower content of reserve materials per plant than in the case of the other two species. The long-persisting, high growth rate in L. digitata may be interpreted as adaptation to life in the sublittoral fringe; however, it obviously prevents the species from perennial colonization of the deepest parts of the kelp zone. The finding that the three Laminaria spp. reduced or ceased growth at different times during the year, under otherwise identical conditions of temperature, nutrients, light intensity or light quality, suggests the possibility that none of these factors actually trigger the seasonal growth behaviour of these species.

Laminaria hyperborea photosynthesis-irradiance relationship measured by oxygen production and pulse-amplitude-modulated chlorophyll fluorometry

“…Gévaert et al (2003) showed that in Laminaria saccharina the daily patterns in PAM fluorescence are related to photo-regulation via the xanthophyll cycle. reported by Lüning (1979) for Laminaria hyperborea kelp blades using gas exchange experiments with , assuming a DW:area ratio similar to that obtained in this study (0.008 g DW cm −2 for the blades). This is >1 order of magnitude higher than the values obtained in the present study, with P max not exceeding 2 mg O 2 g −1 DW h −1…”

“…P max estimations using RLCs from the blade alone (Fig. 2) may reach values > 7 mg O 2 g −1 DW h −1 -still considerably lower than the estimations by Lüning (1979), yet closer to the 12 mg O 2 g −1 DW h −1 value obtained when considering the higher limit of the dry weight:area ratio. Lüning (1979) , values which are much lower than those obtained in the present study, i.e.…”

The effects of warming on the ecophysiology of two co-existing kelp species with contrasting distributions

“…Moreover, the cool-water species exhibited increased production of known an ecologically-important period for many Laminaria species which exhibit fastest annual growth rates through spring and into early summer (Lüning 1979). As such, the observed 397 reduction in growth rates and photosynthetic efficiency at higher temperatures for L. 398 digitata during this period could have wider implications for benthic primary production and 399 the availability of kelp-derived material for consumers.…”

The German Case Study: Pioneer Projects of Aquaculture-Wind Farm Multi-Uses

“…While growth of L. hyperborea totally stops in July, growth of S. latissima decreases substantially but does not cease. In contrast, the growth period of L. digitata from Helgoland extends from spring to summer and in September, it exhibits a growth rate of still 50% of the optimum (Lüning 1979). The seasonal variations in abiotic conditions affect growth performance, particularly in algae from high latitudes with a more pronounced seasonality of temperature, irradiance and photoperiod (Bartsch et al 2008).…”