Copepod Egg Production Rate (Process Cruise)

Methods

Copepod Collection

Live copepods were collected with a 333-µm mesh, 71-cm diameter bongo net with non-filtering cod ends. The bongo net was lowered at 50 m min−1 to approximately 210 m, held at depth for 3 min, and then recovered at 20 m min−1 while the ship moved at 0.5–1 m s−1. The contents were immediately diluted with seawater that was collected below the thermocline the preceding night and placed in a cooler. Adult females were promptly sorted individually into 20 mL Petri dishes containing seawater collected from the chlorophyll maximum layer the preceding night. The dishes were placed in a dark incubator at 13.5 °C.

Egg Production Rates

Dishes were checked for eggs by microscope and the chlorophyll maximum water replaced every 12 h. After 24 h, C. pacificus and M. pacifica were removed from their dishes and preserved in scintillation vials filled with seawater and several drops of 37% formaldehyde. E. californicus was incubated for 24 h for Cycles 1 and 2 in 2011 and for 72 h thereafter. EPR for all species was expressed as eggs female−1 d−1. Clutch sizes were defined as the number of eggs laid by a single female within a 12 hour check interval.

Hatching Success

All eggs were incubated an additional 36 h after their discovery to allow them to hatch. Several drops of acetic acid were added to the dish to stain the nauplii and unhatched eggs to facilitate identification for assessment of hatching success. Hatching success is presented as the percentage of successfully hatched nauplii to the total of nauplii, partially hatched, and unhatched eggs.

Prosome Length Measurements

Following each cruise, prosome lengths of preserved females were measured under a microscope using an ocular micrometer.