Investigation of the Helgoland kelp forest along a depth gradient

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Annual monitoring of the sublittoral macrophytobenthos of the island of Helgoland revealed a change in biomass and depth distribution. This study was performed to identify possible changes in the kelp forest in the north-east part of Helgoland compared to 2005 along a depth gradient between 0.5 and 10 m. The mean kelp biomass increases from 4 kg FW m-² to 6 kg FW m-² between 2005 and 2018. Especially in 6 m - 10 m the kelp biomass has increased. This was also reflected in the increase in the leaf area index from 1.9 to 3.3 between 2005 and 2018. This also indicated a depth expansion of the kelp forest. At the same time, mean water transparency had improved in the last 5 years (2014-2018) by 0.2 m in February and 0.7 m in March compared to the period 2001-2005. Similarly, the mean sea surface temperature in the same period (2014-2018) was 0.3 to 1.4 ° C higher from summer to winter than the long-term average (2005-2018). Additionally, the mean understorey biomass increased from 0.03 kg DW m-² to 0.11 kg DW m-² between 2005 and 2018. Especially at 0.5 m, 2 m, and 4 m the understorey dry biomass was 13-fold, 9-fold and 4.7-fold higher in 2018 than in 2005, respectively. The increase in sea surface temperature and water transparency occurred during the growth phase of L. hyperborea during winter and spring and could be responsible for high biomass, high LAI and depth expansion.

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Thesis (Master)
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Steinberg, R. (2019): Investigation of the Helgoland kelp forest along a depth gradient , Master thesis, University of Oldenburg.

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