1. Egg production rates of the larger copepods in the Gulf of Alaska: Calanus marshallae, Calanus pacificus, Eucalanus bungii and Neocalanus flemingeri Russell R. Hopcroft & Cheryl Clarke Institute of Marine Science, University of Alaska Fairbanks All data adjusted to 5°C Figure 1. LTOP sampling area. Typical experimental sites indicated in purple Question: What are the differences in reproductive strategy for the larger surface-dwelling copepods in the Gulf of Alaska? Methods: The study region in the Northern Gulf of Alaska was occupied 7 times per year from 2001-2004. Zooplankton was collected from the upper 50 m during daytime with a 0.5m ring net. Many species of larger copepods are somewhat sporadic in the samples, but when possible 24-48 females where incubated for 24 hrs to assess egg production. In general, females were incubated in towers that separated them from their eggs after laying. Neocalanus species spawn at depth during winter without feeding, so females collected in early December where maintained in the laboratory and eggs were harvested on several dates each week. Female weight was predicted from species specific length-weight relationships. Egg weight was calculated assuming 0.14 pg C µm -3. Daily specific egg production (SEP) was calculated from these weights. Conclusions: Calanus marshallae, Calanus pacificus and Eucalanus bungii utilize the environmental gradients within the Gulf of Alaska differently, nonetheless the data suggests food saturated egg-production rates of 10-20% per day. This is the same range observed for all other smaller calanoid copepods in this system. Neocalanus flemingeri employs a strategy that uncouples it from the environment to which other copepod species respond. As a daily rate, egg production is low, but substantial when accumulated over the reproductive period. This strategy could be as efficient as that of other co-occurring species if the life-expectancy of those other species is short, and egg production generally below saturated rates. Neocalanus flemingeri Results: Neocalanus flemingeri. From March-June, Neocalanus species were the most common large copepods in the Gulf of Alaska. Of the 4 species presented here, Neocalanus flemingeri was the heaviest species and laid the largest clutches (up to 400 eggs), with lifetime fecundity of up to 1200 eggs. N. flemingeri females do not feed, yet they released an estimated 50-60% of their original mass as eggs. SEP, however, averaged only 2% per day because it was spread out over several clutches during more than a month. Calanus marshallae was the next most commonly observed large copepod, occurring throughout the year, but largely confined to the inner shelf and Prince William Sound. It laid clutches up to of the 100 eggs, that represented up to 20% of the females weight, and was clearly related to chlorophyll concentration. Calanus pacificus is a more southern species imported into the Gulf during summer and fall. It was distributed broadly across the shelf. Clutches were typically smaller then its congender, and presented up to 25% of its body weight. Such high rates were confined to high water temperatures, such that after Q10 correction, they are lower than for C. marshallae. Limited range of observations for chlorophyll precluded establishing a clear signal to food concentration. Eucalanus bungii was confined primarily to offshore oceanic waters. It produced clutches intermediate in size between the calaniids, but despite the potential for large clutches (up to 200 eggs), egg production was extremely variable between individuals. Eucalanus populations often showed extremely limited gonadal development, but when phytoplankton blooms occurred offshore, gonadal development increased significantly.