Population dynamics model of Copepoda (Neocalanus cristatus) in the northwestern subarctic Pacific

Transcription

1 Population dynamics model of Copepoda (Neocalanus cristatus) in the northwestern subarctic Pacific Zooplankton production symposium S , May, 27, Hiroshima Michio J. Kishi 1)2) and Takeshi Terui 1)3) 1)Hokkaido University 2)FRSGC, JASTEC 3)Japan IBM

2 1. Copepoda, Neocalanus cristatus Large grazing copepods Metridia pacifica C6F Eucalanus bungii C6F Neocalanus cristatus C6F 5 mm Neocalanus Neocalanus flemingeriplumchrus C6F C5 Neocalanus species are the dominant large grazing-copepods in the subarctic North Pacific. Annual lifecycle. They undergo an extensive ontogenetic vertical migration (1 ~ 2 m). N. cristatus is the largest copepod. Surface Deep Egg N1-N6 C1-C5 C5(solid) C6 Neocalanus Winter Spring Summer Autumn

3 3 2. Environmental condition and outline of model NEMURO Boundary conditions Solar radiation(w/m 2 ) N 1 -N 6 Winter C 1 -C 5 Spring Summer C 5 (solid) Neocalanus CEgg 6 Autumn Model has two boxes, Surface box = NEMURO and C1-C5, Deep box = eggs, nauplii, solid, adult..6 temperature( ) January April July October Simplified boundary conditions simulated observed value.

4 3. Ecosystem model, NEMURO (North Pacific Ecosystem Model Used for Regional Oceanography) PDM Developed by the PICES Model Task Team (Kishi et al., 27). Nitrogen based box model for the euphotic layer. ZL is set to descend out of the model on 31th August, and returned on 1st April every year as ontogenetic migration.

5 4-2. NEMURO coupled with PDM We consider that copepodite in larger stage can potential graze body-larger group of plankton. Each C1 to C5 lose by predation of ZL to ZP. Solved with an Euler forward scheme, with a time step of 1 hour, running for 5 years. NEMURO PS C1 C2 C3 C4 C5 Nauplii migration ZS Eggs PL migration Adults Solid ZP ZL NH4 excretion POM Egestion or Dead biomass Transfer by growing in the surface water Transfer by aging in the deep water

6 4 3. Comparison between NEMURO with/without PDM These figures represent seasonal variations of biomass of PS, PL, and ZL in the NEMURO and NEMURO - PDM. 25 NEMURO ) 3 Biomass (mgc/m Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec NEMURO - PDM PS PL ZL Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec In spring, nutrients are supplied from deep water. Thus phytoplankton blooms occurred. The peak of PL in NEMURO-PDM is greater than that in NEMURO. In NEMURO- PDM, C1-C4 mainly prey on PS, and PL is free from the grazing pressure from ZL. Grazing pressure to PL in NEMURO-PDM is weaker than that in NEMURO.

7 4 4. Comparison between NEMURO with/without PDM These figures represent seasonal variations of biomass of PS, PL, and ZL in the NEMURO and NEMURO - PDM. 25 NEMURO ) 3 Biomass (mgc/m Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec NEMURO - PDM PS PL ZL Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec In NEMURO, ZL graze PL and PS in a ratio of 4 to 1. This causes the oscillation of PL and ZL. and larger PS biomass from June to September. ZL descend out August, So PL increase in autumn. In NEMURO-PDM, grazing pressure by C5 is strengthened in June. the diapause begins from June and the grazing pressure on PL is weak. Thus PL biomass remains high through autumn.

8 4 5. Annual cycle of abundance of all stages The model represented the annual cycle of abundance. Abundance(ind/m 3 ) 8 Nauplii C3 6 Eggs C4 Solid Adult 4 C2 C5 2 C Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Left vertical axis = Abundance of Eggs, Copepodites, Solid and Adult. Right vertical axis = Abundance of Nauplii The number of nauplii increases exponentially. Because egg production and the transfer from eggs to nauplii continues simultaneity. The nauplii stage lasts longer than eggs, and therefore nauplii accumulated.

9 4 5. Annual cycle of abundance of all stages The model represented the annual cycle of abundance. Abundance(ind/m 3 ) 8 Nauplii C3 6 Eggs C4 Solid Adult 4 C2 C5 2 C Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Tracing the peak, the developmental time from C1 to C5 is 41 days. The shortest developmental time estimated from sampling is 44 days at 6 o C (Saito and Tsuda, 2). This is due to growth rate not regulated by food limitation. That is, food was always sufficient in the model.

10 4 5. Annual cycle of biomass Vertically integrated biomass for each life stage. EGG NPN C1 C2 C3 C4 C5 SOLID ADULT 5 Biomass(mgC/m 3 ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total biomass begins to increase exponentially from April Surface biomass transferred to deep layer from August. Solid and adult make up most of the zooplankton biomass for about nine months. We represented annual cycle of biomass, growth in surface water and life in water.

11 4-6. Discussion In our model, the lack of food limitation resulted in rapid growth of copepodite. The ZL component of NEMURO is assumed to be dominant large copepods. In this study, we replaced the ZL with the PDM representing only the species N. cristatus. Consequently, there is no competition for foods among copepods. Observations suggest PL does not dominate in the Oyashio region in summer. By including the other copepods species in the PDM, the biomass of PL may decrease more during summer.

12 2 Cohort structured PDM Sum of eggs Spawned date

13 2-2Cohort structured PDM NEMURO と関 係する要素を 結合させる

14 Annual cycle of abundance of all stages

15 Difference of growth by birthday 誕生日によって異なる成長率 4 Weight (mgc) 月 1 日 3 月 1 日 4 月 1 日 5 月 1 日 6 月 1 日 7 月 1 日 8 月 1 日 9 月 1 日 12 月 1 日 day Time dependent value of wet weight from C1 to C5

16 誕生日 C1への移行日 Copepodid 期間 Solidへの移行日 1 月 1 日 2 月 28 日 16 6 月 14 日 3 月 1 日 4 月 28 日 67 7 月 4 日 4 月 1 日 5 月 29 日 7 8 月 7 日 5 月 1 日 6 月 28 日 78 9 月 14 日 6 月 1 日 7 月 29 日 71 1 月 8 日 7 月 1 日 8 月 28 日 7 11 月 6 日 8 月 1 日 9 月 28 日 月 16 日 9 月 1 日 1 月 29 日 97 2 月 3 日 12 月 1 日 1 月 28 日 月 5 日

17 Thank you See you tomorrow