A NEW INCUBATION SYSTEM FOR THE MEASUREMENT OF COPEPOD EGG-PRODUCTIONAND EGG HATCHING SUCCESS IN THE FIELD

The design and testing of an incubation system for studying copepod eg g production and hatching success that allows undisturbed incubation a nd monitoring of eggs under field conditions for extended periods of t ime is described. The incubation system was tested with copepods from polar (Weddell Sea), temperate (Irish Sea) and subtropical (Atlantic C oast, Gulf of Mexico and Gulf Stream) seas between 1993 and 1995. Indi vidual female copepods sorted from plankton tows were incubated at amb ient temperature and photoperiod (5% incident light) for 24 h in presc reened (size determined by egg diameter) water from the sampling locat ion. The incubation system consists of an upper spawning chamber that houses the female and a lower brooding chamber where the eggs incubate . After 24 h, the chambers are separated and the eggs are permitted to incubate some 24-96 h longer while being monitored under a microscope to determine the onset of hatching. When nauplii are detected in all containers, eggs and nauplii are incubated an additional 24 h to allow adequate time for the eggs released near the end of the spawning peri od to hatch. Nine experiments were conducted to compare our incubator and protocol with a ''standard'' technique for measuring egg productio n. Mean egg production rates measured by both techniques were not stat istically distinguishable in 8 of the 9 runs. Hatching success was var iable between and within species. Mean hatching success was surprising ly low (62.7%) when taken over the eight species, which suggests that a substantial portion of egg production may not be viable. Apparently, some egg disintegrated during the extended incubation in 43% of our e xperiments, emphasizing that when measuring hatching success, it is im portant to perform counts upon the removal of the female so as not to underestimate the rate of egg production or to overestimate hatching s uccess. The present technique permits one to estimate egg production, as well as, hatching success and the disintegration of delicate non-vi able eggs. (C) 1998 Elsevier Science B.V.