Community science approach reveals temporal and eutrophication-related spatial patterns in bladderwrack-associated invertebrate fauna

Coastal zones are affected by a variety of anthropogenic drivers. While scientific assessments of the large-scale impacts are often insufficient due to limited resources, community science approaches (i.e. engaging voluntary participation by the general public in scientific research) may allow studying processes on larger geographic and/or temporal scales. In this study, a community science campaign was launched to assess geographic and temporal patterns in subtidal bladderwrack (Fucus vesiculosus) -associated invertebrate fauna along the coastal eutrophication gradient of the Finnish Baltic Sea coast in 2020–2021. The data collected by the community scientists were quality-controlled and generally similar to scientist-collected data. However, most taxa had somewhat lower abundances than data collected with another, more established sampling method. The community composition of fauna differed between areas with varying eutrophication status, and the total abundances of fauna were highest in the areas with the lowest eutrophication impacts. The data also revealed spatial and temporal patterns of individual taxa. For example, the abundance of blue mussel (Mytilus edulis) was highest in less eutrophied areas, while the abundance of non-indigenous Harris mud crab (Rhithropanopeus harrisii) was highest in the areas with moderate eutrophication impacts. A two-fold increase in the abundance of isopods that graze on bladderwrack was observed between the study years, indicating a sizeable temporal variation in bladderwrack grazing pressure. The study provides novel information on bladderwrack-associated invertebrate fauna and the applicability of using community science in marine subtidal research. The results suggest that community science is an effective approach to assessing subtidal community-level patterns, and its continued use is recommended to complement data collection across large spatial and temporal scales in marine key habitats.