Copepod egg production in Exmouth Gulf, Western Australia

Ten stations were sampled in Exmouth Gulf (7 on the eastern side and 3 on the western). At each station water temperature and salinity were measured at 1m depth intervals and secchi depth recorded. Values for Chlorophyll a, particulate carbon and nitrogen were determined.

Egg production rates by 4 of the dominant copepod species were measured by bottle incubations (Acartia fossae, Parvocalanus crassirostris) and the egg-ratio technique (Oithona attenuata and Oithona simplex). Egg production data was used to calculate adult females grazing rates of the total particulate carbon each day.

Plankton abundance and biomass did not differ greatly within the gulf; however, highest values of chlorophyll a, particulate carbon and nitrogen, and copepod egg production rates occurred in the south-east of the gulf. Though egg production rates were low and apparently severely food-limited, resuspension of bottom sediments or export of material from adjacent salt flats may fuel production in shallow inshore areas of the gulf. P. crassirostris appeared to be omnivorous and 0. attenuata primarily herbivorous, but the trophic resources used by 0. simplex and A. fossae could not be identified. From the egg production data, it was calculated that adult females of the four dominant copepod species graze 12% of the total particulate carbon each day.