DISTRIBUTIONS AND POPULATION STRUCTURES OF 2 INTERTIDAL ESTUARINE POLYCHAETES IN THE LOWER ST-LAWRENCE ESTUARY, WITH SPECIAL REFERENCE TO ENVIRONMENTAL-FACTORS

An intensive study of the spatial distribution of Nereis virens (Sars) and Nephtys caeca (Fabricius) was conducted during the spring and autumn of 1986 in the lower St. Lawrence estuary. Statistical analysis showed that spatial variations in density, individual body weight and sexual maturity, particularly in the case of Nereis virens, are correlated with the intertidal level, with certain sediment characteristics, and with the thickness of the colonizable sediment layer. The density of N. virens increases in an offshore-onshore direction, whereas that of Nephtys caeca decreases in the same direction. For both species, mean body weight increases downshore from the upper intertidal level. Other specific relationships exist in relation to sediment characteristics. Sexually mature Nereis virens are found only at the lower intertidal level; sexual maturity in Nephtys caeca was not studied. There were no changes in spatial distribution patterns between spring and autumn. The spatial distribution of Nereis virens parallels depth contours and may reflect its ability to inhabit environments which become more physically unstable in an offshore-onshore direction. This spatial distribution is consistent with a model whereby larvae are recruited in the upper intertidal zone and juveniles migrate downshore. © 1990 Springer-Verlag.