The life-history of Polydora ciliata has been studied in the Bassin de Chasse, Ostende. Three or even four generations succeed one another during the period from April to September. Their planktonic larvae can be found throughout the year, they have a life of 12 to 14 days. Larvae from 3 to 9 segments are growing 2 segments a day, larvae from 10 to 16 segments 1 segment a day. During the first period they feed on nannoplankton or detrital particles, during the second period they are carnivorous, but also detritiphagous and phytophagous. After 3 weeks of sedentary life egg-laying takes place. When one or two broods have been produced most animals die. The eggs hatch after 1 week. The worms are detritiphagous and scrape the food directly on the substrate with their palps. The settling on the substrate is followed by the accumulation and active fixation of mud during May-June. The following generations do not produce a heavy settlement due to interspecific competition and heavy mortality of the larvae. The density of settled Polydora may amount to 1 million individuals per m2. This causes the destruction and death of the remaining fauna. Its prolific occurrence responsible for the silting up of rocky intertidal shores, is related to the mud suspensed in the water. Being typically euryoecious Polydora can withstand diverse pollutions longer than many other organisms.
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