The Life-Cycle and Population Dynamics of Streptosyllis Websteri (Polychaeta: Syllidae) from a Northumberland Beach

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Abstract
The population of Streptosyllis websteri at Newton, Northumberland shows epigamous reproduction and has an extended spawning season from April to July, during which there are two main peaks of spawning activity. Most individuals spawn twice in the breeding season at the beginning of their third year of life, although some individuals may contribute to the second spawning peak of the breeding season at the beginning of their second year. Growth rates are remarkably uniform, and year classes are usually clearly distinguishable using setiger number frequency distributions. Observations on growth and mortality suggest that there is competition for resources amongst the new recruitment class over the first few months of life, but that overall survival through the first year is density independent and likely to be determined by external factors. Larval development is largely benthic, and it is unlikely that there is any prolonged truly pelagic larval phase.