Macrobenthos and Morpho-Sedimentary Recovery Dynamics in Areas Following Aggregate Extraction Cessation

Abstract

Marine sand and gravel extraction plays a crucial role in supplying raw materials for construction and coastal protection. However, this activity can profoundly impact the marine environment, altering both seabed structure and biodiversity. While the immediate effects of aggregate extraction are well-documented, the recovery dynamics following extraction cessation remain less understood. Therefore, this study investigates the recovery of macrobenthic communities and morpho-sedimentary characteristics in two areas after cessation of aggregate extraction in a tidal sandbank environment. By combining long-term monitoring data, including multibeam echosounder surveys and grab sampling, we assessed recovery trajectories over up to eight years post-extraction. Our findings highlight that while extraction-induced depressions persist without infill, biological and physical recovery begin almost immediately after extraction stops induced by local sediment reorganisation within the depression and colonisation of opportunistic species. The extent of recovery depends on the time elapsed but after 8 years a return to reference conditions is observed. We hypothesise that seabed enrichment with coarse materials through screening during extraction helped facilitate the recovery via the hiding-exposure mechanism. While signs of recovery are evident, our analysis highlights some site-specific variations influenced by differences in sediment composition, local hydrodynamics, and extraction intensity, suggesting that full restoration to pre-extraction conditions may not always occur. Instead, new stable ecosystem states, approximating reference conditions, could be adopted as alternative recovery benchmarks. These findings underscore the importance of adaptive management strategies, that are tailored to the recovery potential of dynamic sandy environments.

Keywords: Belgian Part of the North Sea, Marine aggregate extraction, Seafloor Integrity, Recovery processes, Environmental impact, On-site screening