Biodiversity & Conservation

For a full description of this biotope including characterizing species, distribution, survey information and references visit JNCC

Upper estuarine mixed hard substrata colonized by very sparse communities of animals with low species richness and with a few seaweeds in very shallow water. In the Tamar estuary the hydroid Hartlaubella gelatinosa and bryozoan Conopeum reticulum are found on stones. In the River Dart the bryozoan Bowerbankia imbricata is most abundant. A similar brackish-water rocky biotope is recorded from the Bann Estuary, Northern Ireland. There are considerable differences in species composition between sites, but all occur in brackish turbid-water conditions. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Little direct information on the ecology of this biotope was available and reference has been made to other hydroid communities, especially estuarine fouling communities where appropriate. The biotope has been described from only two records in the MNCR database (JNCC, 1999). Similarly, the hydroid Hartlaubella gelatinosa has been little studied and inferences have been made from similar species of Obelia (Gili & Hughes, 1995; Stephanjants, 1998). Other frequently occurring species in the few records of the biotope are Alcyonium mytili, Balanus crenatus, Electra crustulenta, Lanice conchilega, Clava multicornis and Obelia dichotoma. The distribution of Conopeum reticulum with respect to salinity is imprecisely known, since it has been confused with other brackish water bryozoans e.g. Conopeum seurati and Electra crustulenta (Ryland, 1970; Hayward & Ryland, 1998) and could have been mis-identified in this biotope.