Experimental Disturbance-Induced Shifts in Benthic Functional Diversity: the importance of marine protected areas in soft-bottom ecosystems

Benthic communities form the foundation of food webs in coastal and shelf seas worldwide. However, these communities face severe threats from anthropogenic bottom-disturbing activities. Marine Protected Areas (MPAs) effectively safeguard benthic communities against such disturbances. Nevertheless, the effectiveness of MPAs for the recovery of benthic communities in highly dynamic soft-bottom areas is much debated, as these communities are thought to be adapted to natural dynamics and therefore resistant to human impacts. In this study, we examine whether MPAs in highly dynamic seas support sensitive communities that are affected by bottom-disturbing fishing gear. Utilising a Before-After-Control-Impact (BACI) experimental design, we investigated the effects of disturbance caused by a shrimp trawl gear on macrozoobenthic communities within MPAs in a dynamic coastal soft-bottom sea over two years. We assessed changes in taxonomic and functional diversity, as well as community composition, across three levels of trawling intensity and frequency (low intensity and high frequency, high intensity and low frequency, and high intensity and high frequency) compared with undisturbed control areas. The study was carried out in the lower dynamic areas of the study system, where we found that, even light trawling gear impacted functional diversity and community assembly of macrozoobenthic communities, leading to shifts in functional groups. Contrastingly, taxonomic diversity metrics were not affected. We found that taxonomic and functional turnover increased stronger over time than the undisturbed control, with the highest turnover in the most frequently disturbed treatments. Long-living species were negatively impacted by disturbance, and the abundance of scavengers and predators increased in trawled areas, with possible radiating effects into undisturbed areas, while suspension feeders declined. Our findings demonstrate that anthropogenic disturbance remains a relevant ecological pressure, even in areas that may appear resilient due to their dynamic nature. MPAs can then provide ecological benefits by protecting sensitive and functionally important species.

Meijer, K. J., Franken, O., Govers, L. L., van der Heide, T., Willebrands, E., de Wilt, M. E., de Wit, B., Olff, H.

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