Extremely sheltered gravelly sandy mud, subject to variable or reduced salinity. The infaunal community consists of the ragworm Hediste diversicolor, Streblospio shrubsolii, Capitella capitata and Manayunkia aestuarina. Oligochaetes and Corophium volutator are abundant. Given the low sample numbers for this biotope, more records are needed to confirm the characterising species list. Situation: It is probable that there are broad transition areas between this biotope and the corresponding muddy sediment biotope A2.3222. The boundaries may be very indistinct, with this unit present in patches of gravelly mud on areas of mudflat, where the main biotope is A2.3222.