In situ egg production and hatching success of the marine copepod Pseudocalanus newmani in Funka Bay and adjacent waters off southwestern Hokkaido, Japan:: associated to diatom bloom

Clutch size and egg viability were examined for wild females of Pseudocalanus newmani collected from four different stations inside and outside Funka Bay, southwestern Hokkaido, Japan, during pre-phytoplankton-bloom conditions in 1997, and from a single station outside the bay during the period from pre- to post-blooming seasons in 1998, to examine spatio-temporal variability of the reproductive parameters and to detect deleterious effects of diatom blooms on in situ copepod reproduction. Clutch size and hatching success in P. newmani were relatively similar at the four stations in 1997. The eggs almost always hatched completely, but deformed nauplii occurred in 20-40% of the cases. The proportion of deformed nauplii gradually decreased when the females were fed on non-diatom Pavlova sp. in the laboratory, suggesting that the occurrence of deformed nauplii was related to the quality of in situ food particles, including diatoms. Clutch size varied from 12 to 30 eggs female(-1) during the study period in 1998; more than 90% of the variation could be explained by the body size of the females which depended on ambient water temperature. Hatching success also varied, from 15 to 80%, but was not related to either clutch size, female body size, water temperature or diatom biomass. These results suggest that not only egg production but also hatchability should be measured routinely when estimating recruitment of the copepod into the planktonic population, and show that neither clutch size nor egg viability are directly affected by diatom biomass. Although we could not obtain clear evidence of in situ deleterious effects of diatoms on abnormal embryos and nauplii, this might be related to methodological problems and properties or characteristics of prey-predator interactions. Also, deformities of copepod nauplii have not yet been observed for reasons other than feeding on diatoms.