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Trees- ShrubsCommon Brittle Star ( Ophiothrix fragilis )
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The Common brittle star consists of a round disk that is 2 cm long with five thick arms that are approximately 7 cm long (1). The colour of the Ophiothrix fragilis varies, ranging from pink, red, beige, brown and sometimes multicoloured (1).The five arms are covered with long spines. The arms are very bristly with seven rugose segments on each segment (2)
Common brittle stars are very mobile (3). When present on hard rock stratum such as bedrock, the Common brittle star has a smothering effect (3) due to the large densities that calumniate. This significantly reduces species diversity and biomass (3) in these areas. The situation is a little different for soft substratum such as sediment. Here a rich fauna of smaller marine animals (3) may be present beneath the brittle stars.
Breeding of the Common brittle star, Ophiothrix fragilis takes place in the summer (3). The breeding season is between June and October, with a life span of six to ten years (4). Larvae appear in the water column after a week, after gamete release and the fertilisation of the eggs. The larvae then metamorphose into juvenile brittle stars whilst still in the plankton (4).
Can normally be found in crevasses, underneath boulders and can be present on seaweeds, on the lower shore (5). Most commonly found from the lower shore to deep water as individuals beneath boulders or as sessile animals (5) but they can also occur as dense populations.
This species is known to form very dense aggregations in European Waters, over scales of several square kilometres and in densities 2000 mֿ² (6). It is normally found at surface depths down to 500m, in the Atlantic Ocean, the English Channel and the Mediterranean Sea (7).
The Common brittle star is a suspension feeder and during feeding, it anchors itself to the rocks. Then raises several of its arms into the passing current, where its tube feet filters out the suspended food matter (plankton) (8).
Conservation action has not been taken for this common species (9).
Description written by Wanda Mills (2009)
(1) Bay-Nouailhat A., September 2005, Description of Ophiothryx fragilis, Available on line at http://www.european-marine-life.org/30/ophiothryx-fragilis.php, consulted on 24th August 2009.
(2) Picton, B.E. & Morrow, C.C., 2009. [In] Encyclopaedia of Marine Life of Britain and Ireland http://www.habitas.org.uk/marinelife/species.asp?item=ZB2350 (Date accessed 25th August 2009)
(3) MarLIN 2004 Biodiversity and Conservation http://www.marlin.ac.uk/habitatecology.php?habitatid=278&code=2004 (Date accessed 25th August 2009)
(4) Hayward P., Nelson-Smith T., Sheilds C., 1996. Collins Pocket Guide Seashore of Britain and Europe. London: Harper Collins Publishers Ltd. 220pp.
(5) MarLIN, 2009. Biological Traits Information Catalogue. Species Information for Ophiothryx fragilis http://www.marlin.ac.uk/biotic/browse.php?sp=4139 (Date accessed 25 August 2009)
(6) MarLIN Learning Zone – Species Review http://www.marlin.ac.uk/lzspeciesreview.php?speciesid=3976 (Date accessed 25th August 2009)
(7) Allen, J.R., 1998. Suspension feeding in the brittle-star Ophiothrix fragilis: efficiency of particle retention and implications for the use of encounter-rate models. Marine Biology 132: 383-390.
(8) Marinet – An Illustrated Guide to Great British Marine Animals – Echinoderms http://www.marinet.org.uk/mreserves/marineanimals.html#ech (Date accessed 25th August 2009)
(9) Arkive – Images of Life on Earth 2003-2009 http://www.arkive.org/common-brittlestar/ophiothrix-fragilis/info.html (Date accessed 25th August 2009)
