Oligochaetes in littoral mobile sand

Description (English)

A species-poor community of oligochaetes occurring in estuarine conditions where sands and gravel are associated with the lower shore river channel in estuaries. The sediment is relatively coarse and mobile due to strong river flow and subject to variable salinity. The biotope also occurs in fully marine conditions on open shores with mobile, medium to fine, usually clean, sand. Oligochaetes, including enchytraeid oligochaetes, constitute the infaunal assemblage. This biotope has been split into two sub-biotopes, based on the physical environment (a full-salinity and a variable salinity type).
Situation: This unit often occurs in variable salinity conditions, in channels of very fast flowing river mouths at the bottom of otherwise sheltered estuarine shores. In this situation, biotopes under the A2.31 and A2.32 biotope complexes may be present above the river channel. A2.222 also occurs on open, fully marine shores. Where it is situated on the mid shore, units A2.111 and/or A2.221 may be present on the upper shore, and lower down on the shore, A2.2231 and A2.2233 may be found. A2.222 may also occur on the upper shore, with A2.2232 present on the mid shore, and A2.2311 or A2.2312 on the lower shore. A2.211may be found on the upper shore where driftlines of wracks and debris accumulate.
Temporal variation: Wave exposure may be higher on some beaches during winter than during the summer months, leading to the disappearance of infaunal species in winter. Where this happens, the biotope may change to unit A2.221. If conditions become more sheltered, seasonally or permanently, the sediment may become colonised by a greater range of species and the area may change to A2.223.

Source: EUNIS habitat classification