Acknowledgments Awesome research technicians: Carla Maria Delfino and Kayt Chambers

1. Development and growth rates of Centropages abdominalis reared in the laboratory at subarctic temperatures Laura M Slater & Russell R Hopcroft lslater@ims.uaf.edu, Hopcroft@ims.uaf.edu University of Alaska Fairbanks, School of Fisheries and Ocean Sciences, Fairbanks, AK 99775 UAF School of Fisheries and Ocean Sciences Results and Discussion Centropages abdominalis took 42 days to develop to 50% adults at 6.9°C (fig 2). Mortality increased dramatically beginning with the appearance of CV stage at both temperatures (fig 3), and populations were exhausted at 4.6°C prior to reaching 50% adults. It took 51 days to reach CV stage at 4.6 °C (fig 2); assuming that CIV and CV stage durations are similar, then it would take 59 days to 50% adults at 4.6 °C. Time to pre-adult stage could be estimated for all except CI at 4.6 °Cbecause we did not observe cumulative 50% at stage. Stage durations ranged from 6.8 to 7.9 days at 4.6 °C and from 3.0 to 6.2 days at 6.9 °C (fig 4). All remaining relations of time to cumulative % at stage were significant (p < 0.05) except CII at 6.9 °C, which we set at midpoint between stages CI and CIII for analyses. Employing our data in conjunction with that of Liang et al (1996), stage duration decreased with increased temperature (fig 4). A consistent group of curves predicting the relationship between temperature and the development time of each stage (fig 5) was created using a Bêlehrádek’s function with the exponent of –1.58 as determined for this species’ embryonic development time (Liang et al 1994). At both temperatures there was a significant increase in prosome length (P <0.05) with each increased copepodite stage, and males were significantly smaller than females for both CV and CVI stages (fig 6). Instantaneous growth rates average 0.08 d-1 at 4.6 °C and 0.17 d-1 at 6.8 °C, and declined with stage at 6.8 °C.These growth rates agree well with those determined in situ for Centropages abdominalis in the Gulf of Alaska, which average 0.14 d-1 at ~12 °C (Hopcroft unpublished data) as determined from egg production rates. Centropages abdominalis Abstract The rates of development and growth of the copepodite stages of Centropages abdominalis were determined at 4.6 & 6.9 °C under excess food conditions in the laboratory. Development rates were determined by following daily changes in stage distribution, and growth rates were measured by examining the change in size between subsequent stages. The total development time from eggs lain to 50% adults was 59 & 42 days at 4.6 & 6.9 °C, respectively, and the average growth rate was 0.08 d-1 and 0.17 d-1 at 4.6 & 6.9 °C, respectively. Figure 2. Development time of Centropages abdominalis. Both median (black symbols) and minimum (color symbols) observed times are indicated. Data for 10.5 and 16 °C from Liang et al (1996). Elapsed day is from the day that eggs were lain. Figure 1. Map of study location in Seward, Alaska. Introduction Centropages abdominalis is a neritic, omnivorous copepod distributed throughout the Pacific. In the Gulf of Alaska, it is most common in near shore waters during late summer and fall (~ 12 °C), but recruitment begins at cooler temperatures. The objective of our research is to report the development and growth rates of the copepodite stages of Centropages abdominalis measured at temperatures colder than previously examined. Figure 3. Average population size of Centropages abdominalis during the study. Breaks indicate the first appearance of a CV stage. Note that the greatest decline in populations (i.e. mortality) occurs after the appearance of CV stage at both temperatures. Figure 4. Stage durations for Centropages abdominalis. Data for 16 °C was taken from Liang et al (1996). Materials and Methods Copepods were collected in Resurrection Bay, Alaska (fig 1), and eggs harvested from Centropages abdominalis females were maintained at 4.6 & 6.9 º C under a 17:7 h L:D cycle. Each temperature was sub-sampled daily throughout the copepodite stages; population size was estimated, and ~30 animals were removed and preserved. Copepods received an addition of a mixture of Isochrysis and Pavlova diluted in each container to ~ 40,000 cells ml-1 every third day. Feeding was augmented with in situ food (10 – 150 µm) collected from the bay to ensure a more nutritionally-balanced diet. Food concentration was assessed weekly to determine chlorophyll a concentration, which averaged 10.94 mg m-3 & 10.21 mg m-3 at 4.6 & 6.9 °C, respectively. Prosome length of preserved copepods was measured digitally, and dry weight was calculated using a published length: weight relationship (Uye 1982). Development time was determined as the time (day elapsed since eggs were lain) to reach 50% at stage (as predicted by linear regressions). Stage duration was calculated as elapsed time between successive 50% at stage. Instantaneous growth rates were calculated from the average dry weight at a copepodite stage and it’s stage duration. Figure 5. Relationship between temperature and median development time from eggs lain to copepodite stage for Centropages abdominalis. Lines were fit to data using a Bêlehrádek's function. Data at 16 °C from Liang et al (1996). (left to right) Laura Slater, Russ Hopcroft, Carla Delfino, and Kayt Chambers Figure 6. Prosome length of Centropages abdominalis. Asterisks indicate a significant difference in length between temperatures. (n: 16 - 163 at 4.6 °C & 29 - 102 at 6.9 °C) Inlaid table shows instantaneous growth rate (d-1) Acknowledgments Awesome research technicians: Carla Maria Delfino and Kayt Chambers Funding: This research is supported by  the U.S. GLOBEC Northeast Pacific Program, jointly funded by the National Science Foundation and the National Oceanic and Atmospheric Administration under NSF Grant OCE-0105236. Thanks to:  Seward Marine Station staff and researchers, especially Alexei Pinchuk, Linda Lasota, and all the marine technicians  Qutekcak Shellfish Hatchery, Seward, AK Literature Cited Liang, D., S. Uye & T. Onbe. 1994. Production and loss of eggs in the calanoid copepod Centropages abdominalis Sato in Fukuyama Harbor, the Inland Sea of Japan. Bull. Plankton Soc. Jap. 41: 131-142. Liang, D., S. Uye & T. Onbe. 1996. Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. I. Centropages abdominalis. Mar. Biol. 124: 527-536. Uye, S. 1982. Length-weight relationships of important zooplankton from the Inland Sea of Japan. J. Oceanogr. Soc. Jap. 38: 149-158.