Temporal Dynamics of the Quantity and Composition of Beach Wrack: A Monthly Analysis in an Urban Sandy Beach in the NE Baltic Sea

Möller-Raid, T.; Torn, K.; Herkül, K.; Taevere, T.; Martin, G.; Paalme, T., and Schubert, H., 2024. Temporal dynamics of the quantity and composition of beach wrack: a monthly analysis in an urban sandy beach in the NE Baltic Sea. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 488-493. Charlotte (North Carolina), ISSN 0749-0208. Sandy beaches are important for tourism and therefore the beaches are often managed, which also includes beach cleaning and the removal of excessive beach wrack. At the same time sandy beaches are fragile environments and often need conservation to maintain their ecological function. The beach management decisions need to be based on the local circumstances, however the information on beach wrack communities is utterly scarce for the northern Baltic Sea. The study was carried out at Kakumäe in Tallinn, Estonia, NE Baltic Sea. Kakumäe sandy beach is popular among both tourists and locals. The amount of beach wrack (areal coverage and volume per 100 m long beach section) and its composition (all marine- and land-origin species) was studied monthly in 2019-2020. The beach wrack coverage varied from a few patches to 50 %, and the volume of beach wrack varied from 0.1 to 50 m3. The amounts were the largest in the period from October to December and lowest in March. Altogether 128 biomass samples were collected and analysed. A total of 112 taxa (64 invertebrates and 48 species of plants and algae) were described within the beach wrack. Land-based invertebrates (37 taxa) and sea-based plants and algae (40 taxa) dominated in the beach wrack composition. The beach wrack provides a food source and shelter to invertebrates, thereby increasing the biological diversity of sandy beaches. Dominant algal species in the Kakumäe beach wrack were Fucus vesiculosus, Furcellaria lumbricalis, Ceramium tenuicorne, Vertebrata fucoides, Battersia arctica, Cladophora glomerata and from higher plants Zostera marina and Stuckenia pectinata, reflecting the heterogeneity of nearby benthic habitats. Faunal species represented the phylums Mollusca and Arthropoda, about 20% of the found species can be regarded as occasional encounters. The study emphasizes the significance of beach wrack in the region and examines the impact of beach management on the coastal community.