Tracking life history of each particle Particles could be divided into three groups (Fig. 7) The red group’s period of copepodite stage shortened when the birthday delayed a day. Because the environment improved for the copepodite day by day, This group’s growth rate was increasing. In this group lately born particle could be caught up with early born particle until diapause starting. Therefore these particles matured at the same time, and they started reproduction all together. The yellow group, which was corresponding PL bloom, did not have the difference by the period of the copepodite by each birthday. A gap at the egg laying start time depends on a gap at the birthday. The green group‘s period of copepodite lengthened due to the deterioration of environment. The egg laying start time of green group delayed more and more. It succeeded to represent that this process was caused by the appearance time of C1 and environmental conditions (food concentration or temperature). LEM A Lagrangian ensemble model of Copepoda (Neocalanus cristatus) in the Northwestern subarctic Pacific Takeshi Terui 1,2 and Michio J. Kishi 1,3,4 1 Graduate School of Environmental Science, Hokkaido University 2 Core Research for Evolutional Science and Technology, Japan Science and Technology Agency 3 Graduate School of Fisheries Sciences, Hokkaido University 4 The Research Institute for Global Change JAMSTEC 1. Introduction 2. Model 3. Results and Discussion Metridia pacifica C6F Eucalanus bungii C6F Neocalanus cristatus C6F Neocalanus flemingeri C6F Neocalanus plumchrus C5 5 mm BirthdayC1Solid The period of Copepodite Egg laying start day Death day Mean growth rate (/day) 1/12/ / /214/ / /224/209/ /213/7 (NY) /34/299/ /233/9(NY) /175/149/ /1 (NY) 3/19 (NY) /86/410/ /26 (NY) 4/11 (NY) Neocalanus species (N. cristatus, N. plumchrus and N. flemingeri) are the dominant large grazing copepods occurring in the subarctic Pacific (Fig. 1). Their life cycles are annual, and they undergo an extensive ontogenetic vertical migration (Fig. 2). They are reported to be important prey components for pelagic fish. Thus, they are a vital link between primary production and higher trophic production in the subarctic marine ecosystems of the North Pacific and its neighboring waters. We aim to model the dynamics of large grazing copepods in the Northwestern subarctic Pacific. In this study, we have developed a Lagrangian Ensemble Model (LEM) for Neocalanus cristatus, which is the largest copepod in this region. We have developed this model to reproduce the annual life cycle, including ontogenetic migration, and we have discussed each cohort’s period of copepodite stage. Fig.1 Large copepods in the subarctic Pacific Fig.2 Neocalanus species annual lifecycle Fig.3 The inter-compartmental flow of NEMURO and LEM JanFebMarAprMayJunJulAugSepOctNovDec Physical condition Living depth Living Temp. ( ℃ ) Mortality setting Predation by ZP Feeding Molting mechanism Initial weight (mgC/ind) The period of the mature (day) Eggsdeep2naturalno aging Naupliideep2naturalno aging C1surface natural, starvation alwaysPL, ZSgrowing C2surface2 – 10 natural, starvation alwaysPL, ZSgrowing C3surface natural, starvation alwaysPL, ZSgrowing C4surface natural, starvation alwaysPL, ZSgrowing C5surface natural, starvation alwaysPL, ZSgrowing C5 soliddeep2naturalno aging C6deep2naturalno aging Table 1 Model setting and parameter in each stage for N. cristatus The LEM was developed to refer to a model for Calanus finmarchicus proposed by Carlotti and Wolf (1998). This model includes development stages, vertical migration, and NEMURO for other compartments (Fig. 3). Each particle of the Lagrangian model represents copepods of the same cohort age, which means one particle represents a set of copepods of the same birthday. This model was coupled with a lower trophic level ecosystem model of NEMURO as an interactive copepod component. The model can simulate the annual cycle of Neocalanus cristatus. We divided N. cristatus life history into 9 stages (eggs, nauplii, copepodites stage 1- 5, solid, and adults). Eggs, nauplii, solid, and adults could be developed without feeding in the deepwater. We assumed two natural death factors of the natural mortality and starvation. Each particle died by the starvation when 0.03 or less of the copepodite growth rate continued for 14 days. We added predation pressure to the C1 – C5 by ZP, which prey ZL in NEMURO. The temperature and solar radiation are applied as physical forcing for the surface water same as Kishi et al (2007). Only the temperature in the deep water is set as a constant boundary condition (2 ◦C) JanFebMarAprMayJunJulAugSepOctNovDec Eggs Nauplii C1 C2 C JanFebMarAprMayJunJulAugSepOctNovDec C4 C5 Solid Adults JanFebMarAprMayJunJulAugSepOctNovDec PS PL ZS ZL ZP JanFebMarAprMayJunJulAugSepOctNovDec Adults Solid C5 C4 C3 C2 C1 Nauplii Eggs 4. Reference Temperature ( ℃ ) Solar radiation (ly/m) Abundance (ind/m 3 )) Fig.4 Simulated abundance of (a) egg, nauplii and C1 to C3 (b) C4 to C5, Solid and Adults. a y = x R² = /21 2/222/23 2/24 2/25 2/26 2/27 2/28 3/1 3/23/33/4 3/5 3/6 3/7 3/8 3/9 3/10 3/11 3/12 3/13 3/14 3/15 3/16 3/17 3/18 3/19 3/20 3/21 3/22 3/23 3/24 3/25 3/26 3/27 3/28 3/29 3/30 3/31 4/1 4/2 4/3 4/4 4/5 4/6 4/7 Abundance (ind/m 3 )) Fig.5 Biomass of phytoplankton and zooplankton in the surface water for NEMURO with LEM. b Biomass (mgC/m 3 )) Fig.6 Vertically integrated Neocalanus biomass for each life stage. LEM of N. cristatus The shape in the line of eggs and nauplii was jagged wave form patterns (Fig. 4a). The extremal value of eggs was almost corresponding to the egg reproduction cycle. Therefore, there was a possibility that some particles which survived in the previous year started egg reproduction at the same time. Precocious particles reached the C1 stage from middle Feb to middle April, but these could not survive by the starvation (Fig. 4a). The particle which could finish life cycle was appeared from April 20th. Survived particles grew at surface and total biomass was increasing from May(Fig. 4a, 4b). The increase of biomass from September was mainly due to the success to develop to solid (Fig. 4b, Fig. 6) which mainly prey on bloomed PhyL in autumn (Fig. 5). In the winter, they molted to adult and reproduced at depth. N. cristatus population on LEM completed annual life cycle. Duration of Copepodite (day) Fig.7 The period of the Copepodite plotted each birthday. Table 2 History of growth of typical particle. Fig.8 Outline chart of population consolidating process. Carlotti, F. and Wolf, K., Fisheries Oceanography., 7(3/4): Kishi et al., Ecological Modelling., 202: Kobari, T. et al., Progress Oceanography., 57: 279 – 298 Terui, T. and Kishi M. J., Ecological Modelling., 215: Surface Deep C1-C5 N1-N6 Egg ♂♀ C6 C5(solid) Summer Autumn Spring Neocalanus Winter Jan. – Mar.Apr. – Sep. Oct. – Dec.Jan. – Mar. Lately born Early born ♂♀ ♂♀ ♂♀ ♂♀ ♂♀