Resting stages of Tortanus forcipatus (Crustacea, Calanoida) in sediments of Victoria Harbor, Hong Kong

The distribution and abundance of viable and non-viable (so-called resting eggs) embryos of the calanoid copepod Tortanus forcipatus were determined in the laboratory by the enumeration of nauplii that emerge from sediments collected in Victoria Harbor (Hong Kong). Sediment cores sliced down to a depth of 37 cm showed the highest number of viable resting eggs near the surface layer (0-5 cm). The number of viable eggs sharply decreased with sediment depth, particularly at the inner harbor stations, although diapause eggs remained viable as deep as 25 cm. Pb-210 analyses of the sediments indicated that the mean egg age was 4.9 years. The egg mortality of T. forcipatus in the sediments was 0.135 year(-1), or 78.22% annual egg survival, calculated by regressing In (egg density) from sediment age. The range of horizontal distribution of viable resting eggs was 24.25 x 10(3)-58.90 x 10(3) m(-2), with a mean value of 36.8 x 10(3) m(-2) over all stations. The accumulation of viable resting eggs that can persist for an extended period of time provided evidence for the existence of an egg bank of T. forcipatus in the sediments of Victoria Harbor.