SOME ASPECTS OF ECOLOGY OF PELOSCOLEX-BENEDENI UDEKEM (OLIGOCHAETA TUBIFICIDAE) IN THAMES ESTUARY

Although Peloscolex benedeni is one of the commonest marine and estuarine tubificids, little has been published on the ecology of this species. P. benedeni is the dominant littoral species in the Cliffe region of the lower Thames estuary, reaching densities of up to 142 × 103 m-2 in association with Tubifex costatus Claparède and Caulleriella sp. The stages in the reproductive cycle are described. The highest proportion of mature worms in the population occurs in late winter and spring and the peak of breeding worms in early summer. These stages precede the main peak in cocoon density. The proportion of breeding worms and the density of cocoons are greater in the deeper sediment layers than in the superficial layer. Experiments showed that P. benedeni tolerated oxygen concentrations as low as 7·2% of air saturation with negligible mortality over 7 days; at the lowest level tested (1·2% of air saturation) 37% of adult worms and 52% of newlyhatched worms died. © 1978.