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ItemThe ecology of Australonereis ehlersi (Augener, 1913) and Ceratonereis erythraeensis Fauvel, 1919 (Polychaeta, nereidae) living offshore from the Werribee sewage-treatment farm, Port Phillip Bay, Victoria, Australia( 1981)Summary: 1. The ecology of the nereid polychaetes Ceratonereis erythraeensis and Australonereis ehlersi was studied along intertidal and shallow subtidal sandflats offshore from the Werribee Sewage-treatment Farm, Port Phillip Bay, Victoria. 2. Populations were sampled monthly from February, 1976 to April, 1977 at 24 stations along 2 km of shoreline. 3. The mouth of the Little River and the 145 W drain were centred within the study area; secondarily-treated effluent is released from this drain, and flows over the intertidal area. The effluent is high in nutrients and low in suspended solids. 4. Both nereids were abundant at Werribee, but displayed divergent distributions. Ceratonereis was distributed intertidally with very dense aggregations at the 145 W drain (mean densities up to 14,000 individuals/m2) and at Station 2, about 400 m southwest of the Little River. Australonereis rarely was collected at the drain; this nereid was more abundant in intertidal and subtidal areas away from the drain. Mean densities reached up to 3,000 individuals/m2 during periods of recruitment. 5. Factor analysis showed Ceratonereis to be closely associated with muddy-sands of the upper-intertidal area, while Australonereis was associated with well-sorted, fine-sand habitats of the lower intertidal and shallow subtidal regions. 6. Examination of gut material revealed that both species mainly were selective deposit feeders. Ceratonereis ingested a wide range of grain sizes (medium sand to silt and clay) compared with Australonereis (mainly silt and clay). Ceratonereis also consumed dead or living animals, if available, therefore displaying a relatively broad diet. Australonereis strictly consumed fine sediments, and may be a suspension feeding nereid; this behaviour would be compatible with its tubicolous existence in fine-sand habitats. 7. Food for both species is micro-organisms (such as bacteria, protozoans, diatoms, and dinoflagellates) associated with mineral grains, detritus, and organic mineral aggregates. Production by this microbiota is 600 to 700 times greater than similar sand habitats in the Bay. Food, therefore, probably represents an unlimited resource for the particle-consuming nereids. 8. Both nereids live about 1-1.5 years, display rapid growth, reproduce from spring to autumn, and probably die after spawning. Ceratonereis brooded embryos in specially constructed tubes; 13-15setiger-stage juveniles emerged after about 4-6 weeks of incubation. A description of the development of the embryo is given. In contrast, Australonereis produced a free-swimming larva; duration in the plankton and development is unknown. 9. Ceratonereis was a major prey item of red-necked stints Calidris ruficollis, sharp-tailed sandpipers C. acuminata, and curlew sandpipers C. ferruginea. These waders consumed medium- to large-sized Ceratonereis, and most likely are responsible for controlling densities of this nereid in intertidal areas at Werribee. 10. Factors which regulate the distribution of both nereid are discussed. Ceratonereis is considered a "pollution-tolerant” species whose subtidal distribution probably is controlled by invertebrate and fish predators. Australonereis is less tolerant of stressful conditions, and densities at the drain may be limited by physical factors and biological competition for space.