Recruitment of copepod nauplii into the plankton: importance of diapause eggs and benthic processes

Abstract

During the last 10 yr it has been shown that the eggs of many zooplankters (e.g. copepods, cladocerans, tintinnids) occur in bottom sediments of coastal regions. Accumulations of these eggs on the sea-bottom may represent an important source for the recruitment of individuals into the plankton. We examined vertical distribution and viability of copepod eggs at several locations in Buzzards Bay, Massachusetts USA. Cylindrical cores were obtained by divers. In the laboratory each core was divided at 1.0 cm intervals to a maximum depth of 10.0 cm. From each layer 2 subcores were taken. One was suspended in seawater and incubated for several days at 19 OC. Hatched nauplii were collected, counted, and reared for identification. Viable eggs (evidenced by appearance of nauplii) were found at all depths in the sediment. The greatest densities (106 to 107 m-') often occurred several cm below !he water-sediment interface. Egg abundance was not significantly correlated with sediment grain size. The other subcore was sonified so that the eggs of Labidocera aestiva could be removed, counted, and incubated (to determine viability). Laboratory feeding experiments indicate that diapause and subitaneous eggs of L. aestiva remain viable after being consumed by either Capitella sp. 1 or Streblospio benedicti which are common benthic consumers in regions where eggs occur. The relative importance and influence of physical factors (waves, tidal and wind-driven currents) and biological factors (feeding and bioturbating activities of benthic animals) on the distribution, abundance, and viability of eggs on the sea-bottom is discussed.