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Shifting beach wrack composition in the SW Baltic Sea and its effect on beach use

Florian Weinberger, GEOMAR Helmholtz Centre for Ocean Research, Marine Ecology Division, Kiel, Germany
Swantje Sundt, Kiel University, Department of Economics, Kiel, Germany
Nadja Staerck, GEOMAR Helmholtz Centre for Ocean Research, Marine Ecology Division, Kiel, Germany
Christine Merk, Kiel Institute for the World Economy, Kiel, Germany
Rolf Karez, State Agency for Agriculture, Environment and Rural Areas Schleswig-Holstein, Flintbek, Germany
Katrin Rehdanz, Kiel University, Department of Economics, Kiel, Germany

DOI: http://dx.doi.org/10.5751/ES-12759-260443

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Abstract

Beach visitors rate beach quality in large part by its appearance. Removal of natural beach litter (called beach wrack) has, therefore, high priority for beach managers in coastal areas dependent on revenues from tourism. Focusing on the German Baltic Sea coast, the amount of beach wrack has increased by a factor of approximately 3.4 between 1977 and 2012/2013. At the same time, the composition of macrophyte communities underwent a severe change from late successional stages (eelgrass and bladder wrack) toward more ephemeral communities. Correspondingly, the contribution of bladder wrack to seaweed litter alone dropped from 75% in 1977 to 18.1% today, while the contribution of ephemeral and nutrient-opportunistic seaweeds increased by a factor larger than 6.2 to approximately 44%. Such seaweed opportunists could have a higher potential for olfactorial nuisance than late successional macrophytes. To test this hypothesis, odors extracted from equal amounts of nutrient-opportunistic and non-opportunistic species that had been partially degraded under equal conditions were compared in a public survey. Participants graded the smell of opportunistic species, in particular Ceramium tenuicorne, consistently as more intense and less pleasant than the odor of non-opportunistic species. The particularly high potential of Ceramium litter and the relatively lower potential of eelgrass litter for deterrence were confirmed in field experiments. We conclude that the documented compositional shift in macrophyte communities at German Baltic Sea coasts since the onset of eutrophication has caused a shift of beach wrack composition toward species with a higher potential for olfactorial deterrence, which could explain recent concerns of beach managers about beach wrack despite the limited increase of biomass in the study area.

Key words

beach management; beach user behavior; beach wrack; coastal eutrophication; nuisance seaweed; seaweed odor

Copyright © 2021 by the author(s). Published here under license by The Resilience Alliance. This article is under a Creative Commons Attribution 4.0 International License. You may share and adapt the work provided the original author and source are credited, you indicate whether any changes were made, and you include a link to the license.

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