Dense aggregations of upogebiid shrimp burrows observed in the nearshore zone off a sandy beach

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Upogebiid shrimp (Decapoda: Upogebiidae) are important ecosystem engineers in shallow marine environments because their filter feeding reduces the abundance of phototrophic microorganisms in the water column. Although many previous studies have examined upogebiid populations in intertidal settings such as tidal flats and estuaries, quantitative observations of offshore populations along wave-dominated open coasts remain sparse. Here, we report the abundance of upogebiid burrows in the nearshore zone of a wave-dominated sandy beach, the Kujukuri coast in central Japan. Upogebiid burrows occurred at water depths of 20.1–30.2 m (corresponding to 5.1–13.1 km offshore). The maximum burrow density was 2591.6 openings m⁻² at a water depth of 26.6 m (corresponding to 10.1 km offshore) observed in December 2021. This roughly corresponds to a population density of 1296 m⁻² because upogebiid burrows typically have two openings. The results suggest that a dense shrimp population comparable to the high value reported in tidal flats exists in the nearshore zone of a wave-dominated sandy beach.