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Marine Ecology Progress Series

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MEPS 286:193-201 (2005)  -  doi:10.3354/meps286193

The paradox of Metridia spp. egg production rates: a new technique and measurements from the coastal Gulf of Alaska

R. R. Hopcroft*, C. Clarke, A. G. Byrd, A. I. Pinchuk

Institute of Marine Science, University of Alaska, Fairbanks, Alaska 99775, USA

ABSTRACT: Egg production rates of the copepods Metridia pacifica and M. okhotensis were examined in the Gulf of Alaska over an annual cycle using a new incubation system that separates females from their eggs and keeps the eggs undisturbed prior to observation. Metridia spp. eggs frequently break-down during incubation, leading to severe underestimates of egg production by traditional methods. Egg production by M. pacifica continued throughout most of the year, while that of M. okhotensis was confined to the spring. Egg production rates of M. pacifica peaked in May at 30 eggs female-1 d-1 and averaged 16 eggs female-1 d-1 from March through October. Egg production of M. okhotensis was limited to spring and averaged 28 eggs female-1 d-1 during April and May. Equivalent specific egg production rates for the 2 species over these periods averaged 10 and 11%, respectively, comparable to other calanoid species from this region. For M. pacifica, most of the variability in egg production rates could be attributed to ambient chlorophyll concentrations, after adjusting for the influence of temperature, with food-saturated specific egg production at 5°C equivalent to 17 to 18% of their body weight d-1, and half saturation occurring at 1 to 1.5 mg chlorophyll a m-3.

KEY WORDS: Egg production · Metridia pacifica · Metridia okhotensis · Alaska · Techniques

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