Species diversity in lagoons, which are typically impacted by dredging, captured in Kaarlenniemi, Finland.
Image credit: Joonas Hoikkala, Parks & Wildlife Finland, 2017.

By Elina Virtanen, Niko Kallio, Marco Nurmi, Susanna Jernberg, Liisa Saikkonen, and Louise Forsblom.

Read the full paper here.

Coastal areas play a vital role in people’s lives, yet there is limited understanding of how human coastal recreational activities impact marine biodiversity. In this study, we investigated the relationship between coastal land-use, specifically dredging, and marine biodiversity loss in the context of second homes. We focused on the Finnish archipelago in the northern Baltic Sea, which is a popular area for second homes. Dredging is often performed to improve access to properties, as shallow shores or extensive reed beds can make access difficult.

We were particularly interested in understanding how dredging affects plant and animal communities and where dredging is most likely to occur. To do this, we characterized the current distribution of second homes and examined how accessibility, landscape, and the environment have influenced their location. We simulated the annual increase of new second homes in the most suitable locations, and evaluated the likely ecological consequences if people were to dredge their shores.

Using extensive data on submerged species inventory, we developed models that describe the marine biodiversity of shallow soft seafloors, which are the areas targeted by dredging. Our simulations indicated that new second homes are most likely to be built in the inner archipelago, close to the mainland, due to better accessibility compared to the outer archipelago. We found that the impacts of dredging have been severe in coastal lagoons and shallow bays, which are important biodiversity hotspots. Additionally, we discovered that even small-scale dredging can have severe consequences as they often target marine biodiversity hotspots in the near-shore, shallow zone where there is enough available light.

Our results highlight the importance of stricter control over land-use in the coastal zone to prevent marine biodiversity loss and to ensure sustainable land-use decisions in the future. We suggest that a comprehensive assessment of the potential ecological consequences of coastal land-use decisions is necessary, especially when it comes to dredging. To protect marine biodiversity and sustainably develop coastal areas, it is essential to take into account the ecological values of the areas that are being impacted.