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

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.

Human-Induced Hydrological Connectivity: Impacts of Footpaths on Beach Wrack Transport in a Frequently Visited Baltic Coastal Wetland

“…Although storm Eunice in February lasted longer, the beach wrack area did not increase and no fresh sea grass leaves were visible. One seagrass shoot litters 6-30 leaves per year (Mateo et al, 2006;Weinberger et al, 2021) and the seagrass meadows offshore (see Kuhwald et al, 2021) provide a large source. Still, it seems as if most cast material was already transported onshore by storm Malik, thus beach wrack accumulation might depend more on timing and source availability than on storm strength.…”

“…Beach wrack washed onshore after storm events and trapped along footpaths enhances wetland resilience. Beach wrack itself also provides a variety of ecosystem services such as stabilizing soft bottom substrates, providing food and shelter to different organisms or storing blue carbon (Defeo et al, 2009;Malm et al, 2004;Vanhooren et al, 2011;Gilburn, 2012;Weinberger et al, 2021;Pan et al, 2021). However, not only Baltic coastal wetlands are understudied with regard to carbon sequestration and storage (Graversen et al, 2022;Buczko et al, 2022), but also the role of beach wrack remains overlooked (Duarte et al, 2013).…”

“…The coastal wetland offers a diverse species portfolio, but the seaward wetland edge is largely dominated by common reed (Phragmites australis) with a few patches of salt marsh bulrushes (Bolboschoenus maritimus). The composition of beach wrack is geographically highly diverse and overall the contribution of ephemeral and nutrient-opportunistic seaweeds increased along Schleswig-Holstein's Baltic Sea coast (Weinberger et al, 2021). However, beach wrack at the study site Stein is dominated by seagrass (relative contribution of 89-95%, Weinberger et al, 2021), probably due to the large seagrass meadows north-west off the coast (Kuhwald et al, 2021; see Figure 1B).…”

“…The composition of beach wrack is geographically highly diverse and overall the contribution of ephemeral and nutrient-opportunistic seaweeds increased along Schleswig-Holstein's Baltic Sea coast (Weinberger et al, 2021). However, beach wrack at the study site Stein is dominated by seagrass (relative contribution of 89-95%, Weinberger et al, 2021), probably due to the large seagrass meadows north-west off the coast (Kuhwald et al, 2021; see Figure 1B). Aquatic vegetation is dominated by Zostera marina (Schubert et al, 2015) and to a lesser degree by Fucus vesiculosus and Fucus evanescens (Rohde et al, 2008).…”

Methane emissions from macrophyte beach wrack on Baltic seashores

“…On Baltic seashores, the increasing level of eutrophication has altered the composition of the beach wrack, with an increased proportion of thinner and filamentous macroalgae, making the beach wrack denser and more nutrient rich (Chubarenko et al 2021). At the German Baltic Sea coast, the accumulated beach wrack biomass has increased by a factor of 3.4 between 1977 and 2013, while the composition changed toward a larger proportion of ephemeral and nutrient-opportunistic seaweeds (Weinberger et al 2021). This has posed a problem as beaches have become increasingly fouled and the larger accumulations of beach wrack has resulted in significantly reduced recreational values of such coastal areas (Stenis et al 2021).…”