Understanding the role of the YS Bottom Cold Water ( 10 C) on the survival strategy of Euphausia pacifica throughout the hot summer

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1 Understanding the role of the YS Bottom Cold Water ( 10 C) on the survival strategy of Euphausia pacifica throughout the hot summer Euphausia pacifica Se-J. Ju, H.S. Kim, W.S. Kim, D.H. Kang and A.R. Ko Korea Ocean Research and Development Institute (KORDI), Korea

2 Backgrounds Yellow Sea is one of highly productive Large Marine Ecosystems in the world ocean - total catch is 5%(3 million tons/yr) of global catches(fao) Direct/indirect impact of human activities (land reclamation, pollution, overfishing, high activity of aquaculture, etc) from four countries (China, South Korea, North Korea, Japan). Become recognized the importance of YS on regional climate change/ fishery production/biodiversity - UNDP/GEF YSLME project - WWF YSEPP program

3 Backgrounds YS has a unique physical feature called YSBCW ( 10 C) which forms through winter cooling and mixing and it is persistently observed in the deep central region of Yellow Sea during summer. It provides a refuge (i.e. over-summering sites) for some organisms (i.e. Euphausia pacifica) to survive through the hot summer (>20 C in surface). Euphausia pacifica is one of key species in YS because of the highest biomass among zooplankton and major prey for fishes (anchovy, sardine, etc.)

4 Objective Understand the role of YSBCM on Euphausia pacifica survival through the hot summer Does E. pacifica utilize YSBCM as an overwintering refuge? If they do, how? Lower metabolism, hibernate, shrinkage. Life cycle of E. pacifica Winter Algal bloom adult Eggs Spring disappear YSBCW form Larvae Juvenile Fall develop Larvae Summer Over-summering (?)

5 Field Sampling Field works April & August 10 - Net sampling : vertical tow from bottom (~5m) to surface using conical net (mouth diameter 1m, mesh 330μm) - 24hr. sampling (every 3hrs) using open-closing net CHINA Yellow Sea KOREA A-line Acoustic : 200 khz split-beam transducer (BioSonics, USA) D-line CTD: Temperature, salinity,and Chl- a Net sampling Acoustic transducer R/V Eardo

6 Sample Analysis Analysis in the lab. Preserved samples - Sorted and enumerated E. pacifica with development stages: egg, nauplii, calyptopis, furcilia, juvenile, and adult - Gut content analysis using SEM Frozen samples - Lipid extracts - Total lipid and lipid class analysis (TLC-FID) - Fatty acid analysis (GC-FID & GC-MSD)

7 Vertical profiles of Temp/Sal/Chl-a Spring 2010 North South Central Coastal Water masses well mixed High Chl-a in the middle of YS A-line D-line

8 Vertical profiles of Temp/Sal/Chl-a Summer 2010 North South Central Coastal Water masses - well stratified YSCM - well developed Chl-a Max just below thermocline A-line D-line

9 Spatial distribution of E. pacifica Eggs Nauplii Calyptopis Furcilia Juvenile 36 A A Adult 35 D03 D05 D06 D07 KOREA D06 D07 KOREA ind./m 3 Jeju ind./m 3 Jeju spring Predominant eggs and nauplii Appearance of large adults (~20mm) (especially, gravid females) in the coast summer A few individuals collected Most of them is early stage (furcilia and juvenile) and small adults (<10mm) Some eggs found only in the coast

10 Diel vertical migration (Spring vs. Summer) Spring (April) depth (m) sunrise 0.87 m/min eggs nauplii calyptopis adult (ind/m 3 ) 253 sunset 0.74 m/min 224 Temp.( C) volume backscattering strength (db) :00 07:00 12:00 19:00 21: fluoresence (mg/m 3 ) Summer (Aug.) 0 sunrise sunset Temp. ( C) db depth (m) m/min juvenile adult (ind/m 3 ) m/min 05:00 07:00 12:00 19:00 21: fluoresence (mg/m 3 )

11 Lipid content and composition Lipid contents (5.4 ~ 7.4 % DW) and class compositions in E. pacifica were not significantly different between spring vs. summer. Relative abundance (% of Total FA) - Algal origin fatty acid markers (20:5(n-3), 22:6(n-3), PUFA) were abundant in the spring (no YSCM), while microbial origin fatty acid markers were abundant in the summer (w/ YSCM) spring summer Protozoa Diatom Grouped FAs Dinoflagellate Bacterial Saturated Polyunsaturated spring Monounsaturated Branched summer 0 14:0 16:3+ 16:1(n-9) 16:1(n-7) 16:2+ 16:1(n-5) 16:1(n-3) 16:0n 18:2 18:1(n-9) 18:1(n-7) 18:1(n-5) 18:0n 20:4+ 20:5(n-3) 20:3+ 20:1(n-11) 20:2+ 20:1(n-9) 20:0n 22:5 22:6(n-3) 22:1(n-9) 22:0n 24:1(n-9) Branched

12 Gut contents Spring Summer Diploneis sp. Paralia sulcata Silicoflagellate Adoneis sp. 10um 25um Flagellate cyst 10um Eutintinus sp. 10um 25um Parafavella sp. 50um 10um 50um Detritus Flagellate Pennate diatom Almost diatoms 25um Some diatoms, dinoflagellates, Protozoa, and detritus

13 Findings Major spawning occur in spring. (even it was weak during summer, still some spawning activity occurred in the coastal region) Strong DVM was detected in spring and summer but DVM depth was limited to below thermocline during summer. Krill is herbivorous (mainly diatom) in spring but in summer, it is omnivorous because it could feed on any particles sized from 10 to 200um (protozoa, detritus, dinoflagellate, diatom, etc). Bloom Spring Large phytoplankton Summer Small phytoplankton Nutrient Microbial loop Small zooplankton Microbial loop YSBCM? Detritus

14 Questions raised Where are most of adult E. Pacifica during summer? - Based on acoustic signals, they were condensed near the bottom (2-3m above bottom) - Also they were spatially very patched. - In order to confirm this, we need different sampling devices! A05/day-time Sv (db) CTD signal I Strong signal : high density or large size krill % of data 10 5 I A06/day-time Sv II Weak signal : low density or small size krill % of data 15 II Sv