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

Ecological and functional relationships

Conspicuous members of the community include active and passive suspension feeders that compete intensely for space. The conspicuous members of the community provide substratum for attached bryozoans and hydroids and microhabitats for amphipods, worms and small crustaceans that are most likely scavengers. Apart from competition for space, there is little interaction between members of the community.

Seasonal and longer term change

The most likely seasonal change in this community will be the occurrence of annual algae and the growth of new fronds in perennial algae where the community occurs at shallow depths. Some members of the community, such as the often dominant ascidians Molgula manhattensis and most likely Polycarpa spp and Distomus variolosus, settle and grow rapidly and may also be lost in, for instance, storm events thus freeing space for settlement by other species. Many of the more sparsely distributed species such as the branching sponges are believed to be long-lived and slow growing. For instance, Hiscock (1994) records growth rates of less than 1 mm a year in the branching sponge Axinella dissimilis that can grow to 20 cm tall.

Habitat structure and complexity


The organisms found in this biotope are secondary producers and no information has been found on levels of productivity.

Recruitment processes

Recruitment is predominantly from planktonic propagules.

Time for community to reach maturity

The dominant species in the community (the ascidians) are likely to colonize and grow very quickly (establishment within one year) if propagules are present at the time that bare rock is available. Some of the associated species (for instance, Nemertesia spp., Alcyonium digitatum, Pomatoceros triqueter, other ascidians) will colonize and grow within a few years. However, some of the species associated with the community most likely reproduce and settle infrequently and are slow growing (especially cushion and branching sponges). Little evidence is available for the longevity and growth of these sponges although Hiscock (1994) observes that Axinella dissimilis has a growth rate of less than 1 mm a year.

Additional information

No additional information.

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 25/11/2015]. Available from: <>