Biodiversity & Conservation

Molgula manhattensis and Polycarpa spp. with erect sponges on tide-swept moderately exposed circalittoral rock



Image Keith Hiscock - Molgula manhattensis dominated seabed, middle channel with associated common starfish Asterias rubens. Image width ca 50 cm.
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Distribution map

CR.HCR.XFa.Mol recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats

For a list of 2004 characterising species please see the JNCC website.

Species indicative of sensitivity

To assess the sensitivity of the biotope, the sensitivity of component species is reviewed. Those species that are considered to be particularly indicative of the sensitivity of the biotope, and for which research has been undertaken in detail are shown below (see selection criteria). The biology of other component species of the biotope is also taken into account wherever information is known to the researcher.

Species found especially in this biotope

  • Molgula manhattensis

Rare of scarce species associated with this biotope

Community Importance Species name Common Name
Key structural Molgula manhattensis Sea grapes
Important characterizing Alcyonium digitatum Dead man's fingers
Important characterizing Urticina felina Dahlia anemone
Important characterizing Flustra foliacea Hornwrack
Important characterizing Nemertesia ramosa A hydroid


Molgula manhattensis and similar ascidians including Polycarpa spp. are dominant in the biotope and, without them, the biotope would not be recognised. The range of other animal species present in the biotope is large but the most abundant species appear to be fast growing species that most likely settle readily when space becomes available (for instance after storms have destroyed existing but old populations) and would recover rapidly following an impact. Examples of those species have been included to represent sensitivity. However, many of the species listed as characteristic of the biotope, especially the branching and cushion sponges, are slow growing and recruit infrequently. There is very little literature on those species that are believed to be long-lived and slow growing but, wherever information is known, it has been used in assessments.

Additional information

The Marine Nature Conservation Review (JNCC, 1999) recorded a total of 512 taxa from examples of this biotope including some species groups that would have been identified to species elsewhere.

This review can be cited as follows:

Hiscock, K. 2002. Molgula manhattensis and Polycarpa spp. with erect sponges on tide-swept moderately exposed circalittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 30/11/2015]. Available from: <>