Polydora sp. tubes on upward-facing circalittoral soft rock
Image Keith Hiscock - Polydora sp. tubes on upward-facing circalittoral soft rock, with the sponge Suberites sp. also present. Image width ca 2 m.
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Ecological and functional relationships
In areas of mud, the tubes built by Polydora ciliata can agglomerate and form layers of mud up to an average of 20 cm thick, occasionally to 50cm. These layers can eliminate the original fauna and flora, or at least can be considered as a threat to the ecological balance achieved by some biotopes (Daro & Polk, 1973).
Daro & Polk (1973) state that the formation of layers of Polydora ciliata tend to eliminate original flora and fauna. The species readily overgrows other species with a flat morphology and feeds by scraping its palps about its tubes, which would inhibit the development of settling larvae of other species.
The activities of Polydora plays an important part in the process of temporary sedimentation of muds in some estuaries, harbours or coastal areas (Daro & Polk, 1973).
Polydora ciliata is predated upon by urchins and in Helgoland there is a close relationship between the distribution of Polydora ciliata and Echinus esculentus. Echinus esculentus grazes almost exclusively on the Polydora ciliata carpets and takes its main food not from biodetritus and animals living between the Polydora chimneys but by feeding on the worm itself. To reach the worm, Echinus esculentus has to scrape away between 0.5and 1.2 cm of solid rock and this feeding behaviour is responsible for the bioerosion of rocks in the Helgoland area by an estimated 1cm per annum (Krumbein & Van der Pers, 1974).
Seasonal and longer term change
The early reproductive period of Polydora ciliata often enables the species to be the first to colonize available substrata (Green, 1983). The settling of the first generation in April is followed by the accumulation and active fixing of mud continuously up to a peak during the month of May, when the hard substrata are covered with the thickest layer of mud. The following generations do not produce a heavy settlement due to interspecific competition and heavy mortality of the larvae (Daro & Polk, 1973). Later in the year, the surface layer cannot hold the lower layers of the mud mat in place, they crumble away and are then swept away by water currents. The empty tubes of Polydora may saturate the sea in June. Recolonization of the substratum is made possible, when larva of other species are in the plankton so recolonization by Polydora may not be as successful as earlier in the year.
Habitat structure and complexity
The biotope has very little structural complexity as Polydora tubes aggregate to form layers of muddy tubes on soft rock. Polydora mats tend to be single species providing little space for other fauna or flora. A Polydora mud is about 20cm thick, but can be up to 50cm thick.
Productivity in MCR.Pol is mostly secondary, derived from detritus and organic material. Macroalgae are absent from the biotope. The biotope often occurs in nutrient rich areas, for example, close to sewage outfalls. Allochthonous organic material is derived from anthropogenic activity (e.g. sewerage) and natural sources (e.g. plankton, detritus). Autochthonous organic material is formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients are recycled. The high surface area of fine particles that covers the Polydora mud provides surface for microflora.
The spawning period for Polydora ciliata in northern England is from February until June and three or four generations succeed one another during the spawning period (Gudmundsson, 1985). After a week, the larvae emerge and are believed to have a pelagic life from two to six weeks before settling (Fish & Fish, 1996). Larvae are substratum specific selecting rocks according to their physical properties or sediment depending on substrate particle size.
Larvae of Polydora ciliata have been collected as far as 118km offshore (Murina, 1997). Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates and the larvae of the species settle preferentially on substrates covered with mud (Lagadeuc, 1991).
Time for community to reach maturity
A Polydora biotope is likely to reach maturity very rapidly because Polydora ciliata is a short lived species that reaches maturity within a few months and has three or four spawnings during a breeding season of several months. For example, in colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring. The tubes built by Polydora agglomerate sometimes to form layers of mud up to an average of 20cm thick. However, it may take several years for a Polydora ciliata 'mat' to reach a significant size.
This review can be cited as follows:
Polydora sp. tubes on upward-facing circalittoral soft rock.
Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line].
Plymouth: Marine Biological Association of the United Kingdom.
Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=247&code=1997>