Seasonal cycle of phytoplankton community composition off Newport, Oregon, in 2009

Transcription

1 Seasonal cycle of phytoplankton community composition off Newport, Oregon, in 29 Xiuning Du 1, William Peterson 2 1 College of Environmental science and Engineering, Ocean University of China, Qingdao, Shandong 2661, China. 2 NOAA Fisheries, Northwest Fisheries Science Center, Hatfield Marine Science Center, Newport, OR 97365, USA

2 Why did we do the study? Funded by a harmful algal bloom project MOCHA (Monitoring Oregon s Coastal Harmful Algae). Project interested in Pseudo-nitzschia. When does it bloom? Do blooms of P-n relate to other phytoplankton blooms? Interested in relationships between blooms and upwelling. Basic study of phytoplankton ecology. We also measured copepod egg production during the same cruises needed to know how to interpret copepod egg production using phytoplankton species composition and biomass data. This talk mostly about the seasonal cycle of phytoplankton community structure By chance, the study took place during the onset of a weak El Niño event in August 29

3 Monthly SST anomalies at the NOAA Buoy off Newport (upper panel) and monthly values of the Pacific Decadal Oscillation (PDO: colored bars) and Multivariate ENSO Index (MEI: black line) NOAA Buoy 465 Temperature Anomaly PDO (colors) and MEI (line) Indices YEAR

4 NH5: (5 miles, 62m depth, 44.6 N) located at the very center of the most active upwelling zone; temperature is the lowest and nutrients are the highest. Study area Methods o Went to sea every two weeks in 29 o Preserved surface water in Lugols o Inverted microscope counts o Identification using Rita Horner s book

5 Seasonal upwelling/downwelling cycles in 29 Cumulative upwelling index winter downwelling spring/summer upwelling late summer upwelling autumn downwelling Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Upwelling season started around on Mar. 23 and ended on Oct. 12

6 Seasonal cycle of main group biomass (µg g C L -1 ) in phytoplankton community Overall, higher biomass and dinoflagellate proportions started with warm ocean Carbon biomass Carbon biomass Carbon biomass winter downwelling spring/summer 2/17 upwelling autumn downwelling late summer upwelling 6/2 7/8 58% 7/23 late summer 7/28 94% upwelling 68% Diatoms Dinoflagellates others 12/1 11/4 1/5 8% 3 4 4/ /7 9/22 3/23 8/27 spring/summer 2 autumn 2 upwelling 11/1 downwelling 2/ /26 4/23 6/ /16 Month / Month Month 1/19

7 Seasonal cycle of total Chl a and <5µm fraction concentrations (µg( g L -1 ) in Total Chl a concentration Month

8 Seasonal cycle of total Chl a and <5µm fraction concentrations (µg( g L -1 ) in 29 Chl a <5 micron concentration ~86.2% 5.8%~91.6% Month All the observed higher total Chl a concentrations (9~21 µg L -1 ) had Chl a <5µm contributions of 5~91.6% in total.

9 We could see the progression of diatoms dinoflagellates smaller flagellates assemblages from the alternation of upwelling season and downwelling season. Also, the progression of diatoms smaller flagellates during the course of event-scale upwelling/downwelling cycles.

10 Sampling dates at NH5 in 29 4/23 A 2/17 A 5/16 A 2/4 A 3/24 A 12/1 A 1/5 B 5/26 B 7/8 B 6/2 B 7/23 B 7/28 B 4/4 B 5/7 B 9/1 C 8/27 C 9/22 C 6/14 D 1/19 D 11/4 D 11/1 D Bray-Curtis similarity Four clusters: A: cold winter B: strong cold upwelling C: late upwelling season D: warm autumn Phytoplankton community structure analysis based on cruise by cruise sampling throughout year of 29 2/4 A 5/16 A 3/24 12/1 A A 2/17 A 4/23 A 6/14 D 11/4 D 11/1 D 1/19 D 4/4 B 5/26 B 7/28 7/23 6/2 B B 7/8 B B 5/7 B 9/1 C 8/27 C 9/22 C 2D Stress:.13 1/5 B

11 Total Chl a concentration A A A B A A B B B Month D B B B C C C D B D D A Phytoplankton chlorophyll biomass of the four clusters Cold winter cluster A: low Chl a: <2.2 μg L 1 Strong cold upwelling cluster B: high Chl a: 4.4 ~14.5 μg L 1 Late upwelling season cluster C: high Chl a: 1.3, 3.7, 15.6 μg L 1 Warm autumn cluster D: high Chl a: 2.9, 2.7, 2.1,.5 μg L 1

12 Cluster A (cold winter) Coscinodiscaceae silicoflagellates Protoperidinium spp. Gonyaulax spp. Species contributed most to the similarities for each cluster Cluster B (strong cold upwelling) Chaetoceros debilis Thalassiosira nordenskioeldii Asterionellopsis glacialis Thalassiosira rotula Thalassiosira pacifica/aestivalis Pseudo-nitzschia australis complex Eucampia zodiacus

13 Species contributed most to the similarities for each cluster Cluster C (late upwelling season) Prorocentrum gracile Pseudo-nitzschia australis complex Chaetoceros debilis Thalassiosira pacifica/aestivalis Protoperidinium spp. Cluster D (warm autumn) Akashiwo sanguinea Ceratium lineatum Alexandrium catenella

14 Pseudo-nitzschia abundance (line) and biomass (µg g C L -1 ) (bar) versus time Pseudo-nitzschia carbon biomass Chl a >5 micron concentration Month abundance (cells L -1 ) Month Upwelling, mixing, nutrients, lights, species succession, biological factors

15 Akashiwo sanguinea unusual bloom during autumn (October to November) of 29 Akashiwo sanguinea abundance Average Maximum late summer upwelling autumn downwelling 27 Aug.22 Sep.5 Oct. 19 Oct.4 Nov.1 Nov.1 Dec. (Du et al., 211)

16 Conclusion Strong seasonal cycle with modest blooms (based on chl-a) in February, larger blooms in April-August. Very large bloom in October/November due to Akashiwo sanguinea. Phytoplankton community structure changes related to upwelling intensity and seasonality. It progressed in the order of mixture taxa diatom type mixture taxa dinoflagellate type. No clear relationship with El Niño other than water got unusually warm in August and September; we do not know if the El Niño contributed to the dinoflagellate blooms in August/September (Prorocentrum gracile) and October/November (Akashiwo sanguinea). Pseudo-nitzschia high density (above 1 5 cells L -1 ) occurred during upwelling season and related to upwelling events.

17 Acknowledgements We thank Tracy Shaw (TS), Jay Peterson (JP), Jennifer Menkel and Captain Mike on the Elakha for collecting the samples, JP for processing the CTD data, TS for processing the chlorophyll samples, Joe Jennings for running the nutrient samples and Jennifer Fisher s comments on data analysis. This study was supported by the China Scholarship Council for sponsoring the study abroad for Xiuning Du; the NOAA/MERHAB 27 program project NH7NOS ; Monitoring Oregon Coastal Harmful Algae (MOCHA) and the NOAA/CAMEO program.