Hyperborea

Abstract: This paper describes the macroflora and macrofauna associated with two bull kelp species,Laminaria hyperborea andL. digitata, at the island of Helgoland, North Sea. During a study period of seven months (March–September 1987), 29 macroflora species and 125 macrofauna species were found. The dominant taxonomic groups were Polychaeta (25 species), Bryozoa (17), Amphipoda (14), Hydrozoa (10) and Ascidiae (8). The species maximum was in July. In general,L. hyperborea was preferred as a substrate for settlement toL. digitata. Composition of the communities associated with kelp changed during the season according to exposure to wave action, and according to location on the kelp thallus. The rhizoid community of both kelps bore more species at exposed locations. Wave-exposedL. digitata lacked obvious faunal settlement on both phylloid and cauloid. Phylloid and cauloid ofL. hyperborea were chosen as an attractive substrate at both sheltered and wave-exposed locations, showing an association of encrusting bryozoan and hydrozoan colonies.

Abstract: Rates and drivers of primary productivity are well understood for many terrestrial ecosystems, but remain poorly resolved for many marine ecosystems, particularly those within in coastal benthic environments. We quantified net primary productivity (NPP) using two methods as well as carbon standing stock within kelp forests (Laminaria hyperborea) at multiple subtidal habitats in the United Kingdom (UK). Study sites spanned 9° in latitude and encompassed a gradient in average temperature of ~ 2.5 °C. In addition to temperature, we measured other factors (e.g. light intensity, water motion, nutrients, sea urchin density) that may influence productivity. Although estimates of NPP were highly variable between sites, ranging from 166 to 738 g C m-2 yr-1, our study-wide average of 340 g C m-2 yr-1 indicated that L. hyperborea forests are highly productive. We observed clear differences between NPP and carbon standing stock between our cold northernmost sites and our warm southernmost sites, with NPP and standing stock being around 1.5 and 2.5 times greater in the northern sites, respectively. Ocean temperature was identified as a likely driver of productivity, with reduced NPP and standing stock observed in warmer waters. Light availability was also strongly linked with carbon accumulation and storage, with increased light levels positively correlated with NPP and standing stock. Across its geographical range, total NPP from L. hyperborea is estimated at ~ 7.61 Tg C yr-1. This biomass production is likely to be important for local food webs, as a trophic subsidy to distant habitats and for inshore carbon cycling and (potentially) carbon sequestration. However, given the strong links with temperature, continued ocean warming in the northeast Atlantic may reduce primary productivity of this foundation species, as optimal temperatures for growth and performance are surpassed.

Abstract: Profiles of bottoms near the shore of the Isle of Man and two areas of Scotland are described, together with the vertical distribution of species of Laminariaceae. Laminaria digitata dominates over a narrow zone near lowwater springs. Unstable bottoms, providing they are sheltered enough to be habitable, support mainly L. saccharina. Stable bottoms of either boulders or solid rock support L. saccharina when sheltered (by topography or depth) from wave action and L. hyperborea when exposed. Near Port Erin, Isle of Man, the downward penetration of L. hyperborea on exposed rocks and boulders is limited by an as yet unknown factor which might possibly be associated with a slope of more than to the horizontal.

Abstract: Recent investigations of the intertidal macrophyto- and zoobenthos of the island of Helgo- land (North Sea) revealed that species composition and spatial extent of communities have changed within the last century. To evaluate the situation in the subtidal, a diving study from the late 1960s was repeated with comparable methods in 2005 and 2006. Along 2 vertical transects, the cover of dominant brown seaweeds, Fucus serratus, Laminaria digitata, L. hyperborea, Saccharina latissima (= Laminaria saccharina), Sargassum muticum and Desmarestia aculeata, was semi-quantitatively assessed to define vegetation zones. Within each zone, all macroalgal species were estimated quantitatively in 3 to 6 random 1 m 2 quadrats. Additionally, a replicated biomass survey was performed at 6 depths (0.5, 2, 4, 6, 8 and 10 m below mean low water spring tide (MLWS)). Comparison of recent and historical data showed some characteristic changes. The previously dominant brown seaweed S. latissima showed a decline in the northern part of the island, but is still present at other sites. S. muticum invaded the kelp forest, but is not dominant within this vegetation. The vertical distribution of L. hyperborea increased, and its lower depth limits as well as those of various understory seaweeds deepened by about 2 to 8 m. Biomass data followed this trend. The maximum biomass of L. hyperborea shifted from 2 m below MLWS in 1967 to 4 m below MLWS in 2005. The overall downward extension of the Laminaria forest is concordant with the increase in water transparency observed around Helgoland since 1975.