Biodiversity & Conservation

In areas of mud, the tubes built by Polydora ciliata can agglomerate and form layers up to an average of 20cm thick, occasionally to 50cm. These mud 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 outside 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).

Other species that may be found in the biotope include mud dwelling polychaetes such as the slow moving, burrowing Pholoe synophthalmica and mucus tube building Neoamphitrite figulus. The amphipod Corophium volutator, which builds semi-permanent burrows in mud may also be present in high abundance.

• The early reproductive period of Polydora ciliata often enables the species to be the first in the year 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 substrata is covered with the thickest layer of Polydora 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 of substantial Polydora muds may not be able to 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 close to dense Polydora ciliata aggregations 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.

The biotope has very little structural complexity as Polydora tubes aggregate to dominate firm mud or clay. 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 IMU.PolVS is mostly secondary, derived from detritus and organic material. Polydora ciliata generally feeds on detritus but may also suspension feed on particles in the water. 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 of development 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 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 substrata and the larvae of the species settle preferentially on substrata covered with mud (Lagadeuc, 1991).

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.

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