CR 37:135-147 (2008)  -  DOI:

Changes in depth distribution and biomass of sublittoral seaweeds at Helgoland (North Sea) between 1970 and 2005

Constanze Pehlke1,2,*, Inka Bartsch1

1Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
2Present address: University of Rostock, Albert Einstein Str. 3, 18051 Rostock, Germany

ABSTRACT: Recent investigations of the intertidal macrophyto- and zoobenthos of the island of Helgoland (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 m2 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.

KEY WORDS: Biomass · Change · Depth limit · Macroalgae · Laminaria · Saccharina · Helgoland · North Sea

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Cite this article as: Pehlke C, Bartsch I (2008) Changes in depth distribution and biomass of sublittoral seaweeds at Helgoland (North Sea) between 1970 and 2005. Clim Res 37:135-147.

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