Mapping temporal trends of intertidal Zostera nolteiseagrass and its interactions with oyster aquaculture, sediment characteristics, and macroinfaunal assemblages in the Royal Bay of Grouville, Jersey

Seagrass meadows provide key ecosystem services but are in global decline. In the Royal Bay of Grouville, Zostera noltei forms an extensive intertidal bed overlapping with oyster aquaculture within the South East Coast of Jersey Ramsar site. This study examined changes in Z. noltei extent (1997–2024) using aerial imagery, alongside field surveys of seagrass cover, sediment characteristics, and macroinfauna in the main bed and adjacent aquaculture zones. Extent declined between 1997 and 2012, consistent with previous assessments, but recovery extended from 2021 to 2024, reaching the largest recorded cover (1.30 km²) and expanding lower shore into trestle areas. Expansion was absent south of Le Hurel slip, apart from a small patch, suggesting localised nutrient enrichment by oysters facilitate colonisation. Sediments in Z. noltei habitat were dominated by Well Sorted Medium Sand, with denser and more stable cover in middle and lower shore zones, and greater variability in the aquaculture zone. Oyster aquaculture did not alter primary sediment type, but improved sorting indicating facilitation of localised seagrass expansion. Seagrass colonisation of aquaculture areas enhances infaunal abundance and richness but produced distinct communities from the main bed, shifting toward opportunistic deposit feeders over bivalves, creating hybrid assemblages between seagrass and bare sand habitat. Overall, oyster farming in Grouville Bay has not hindered seagrass recovery, and may facilitate its expansion while restructuring benthic communities.