EOSC Biology 3. Zooplankton Measurements

Transcription

1 EOSC Biology 3 Zooplankton Measurements

2 Zooplankton Biomass and Abundance Two Quantitative Procedures: Biomass Determination (mg C per m 3 or per m 2 ) Abundance (# individuals per m 3 or per m 2 )

3 Biomass Determination by Volumetric Method Measures the settling volume of a sample 1. Pour sample into a graduated cylinder 2. Mix sample 3. Particles settle by gravity over 24 hrs 4. Measure the settled volume 5. Convert settled volume (SV) to mg wet mass (WM) or dry mass (DM) using conversion factors. 1 mg WM = 195 cm 3 SV (or 195 ml) ICES Committee on Terms and Equivalents

4 Biomass Determination by Volumetric Method Rapid Influenced by shape of organisms Any large gelatinous plankton should be rinsed and removed before measuring

5 Abundance Determination Enumeration and identification of organisms in sample 1. Measure a subsample using a Folsom Splitter (coefficient of variation (CV) = 5-18%)

6 Abundance Determination 2. Count at least 100 individuals of most abundant groups (CV = 20%) 3. Estimations of other groups are less precise 4. Compute abundance # individuals m -3 = n k -1 V -1 n = number of counts k = fraction counted (e.g. 0.5 if counted half the sample) V = volume filtered by the net

7 Abundance Determination Can obtain wet weight (WM) or dry weight (DM) by multiplying individual species counts by the average WM or DM of an individual WM or DM can be converted in Carbon weight e.g. DW has 50% of carbon, mg DW * 0.5 = mg C Time consuming, requires experience, but only method that allows parallel quantification and identification Estimates of zooplankton abundance or biomass are highly variable. Have a CV of at least 20%.

8 Zooplankton Conversion factors Raymont, J.E.G Plankton and productivity in the oceans. Volume 2. Zooplankton. 489 pp. Pergamon Press NY. ISBN Checkout R. Peters publications (allometry and zooplankton) Zooplankton biodiversity & trophic state in lakes [Ecology, 88(7), 2007, pp ]

9 Zooplankton Feeding Experiments For carnivorous zooplankton (ingestion rates) To determine the type of functional response of a given zooplankton predator Feeding rate (prey * predator -1 h -1 ) Holling 1959 [Prey]

10 Zooplankton Feeding Experiments Herbivorous zooplankton (grazing rates) Grazing by female Calanus hyperboreus on various food concentrations of (a) and (b) Thalassiosira [Mullin, 1963]. Solid lines: grazing rate = clearance rate; ml cop -1 d -1 Broken lines: rate of intake = ingestion rate; cells cop -1 d -1

11 @ low phytoplankton density zooplankton may Increase F Keep max F Reduce F Exploiting phyto to extinction Phyto can grow despite grazing Lower grazing mortality

12 Rerissinotto (2000)

13 Zooplankton Feeding Experiments Grazing vs. Ingestion rates Decide what organisms you want to investigate Ingestion Rates (eg.chaetognaths feeding on copepods) - Sample live zooplankton (see previous lecture) - Sort species of interest using a wide bore pipette - Incubate zooplankton in bottles with food and measure the decrease in [food] Grazing Rates (eg. copepods feeding on phytoplankton) - Sample live zooplankton (see previous lecture) - Sort species of interest using a wide bore pipette - Collect phytoplankton in the chl a maximum

14 Grazing Rates Experiments 1. Filter seawater through a Nitex screen (variety of porosities) to remove any possible phytoplankton grazers o 2. Pour seawater with phytoplankton in bottles (need initials, controls, & experimentals) 2.5 (if interested in the response of zoop to various [phyto] will need to prepare bottles w/ different phytoplankton densities, using 0.2 μm filtered seawater 3. Measure [chla] in these bottles, this is your initial phytoplankton abundance 4. Add predators at a reasonable [ ]: enough to see a decrease in phytoplankton & not too high to stress the predators themselves (search literature, due to low O 2 ) 5. Incubate for 24 hours, measure final [chla] (can also determine size-fractionated chla, as zoop have higher grazing rates on larger phytoplankton, if you do so you ll need more water) 1 L 1 L 1 L Initial bottles for initial measurements, no zoop 1 L 1 L 1 L 1 L 1 L 1 L Control bottles with no zoop to determine phytoplankton growth during experiment Bottles with zoop

15 Ingestion Rate Experiments - Filter seawater to remove any possible predators and prey - Pour filtered seawater in bottles - Add prey at a reasonable [ ] (or at various concentrations in different bottles) - Add predators at a reasonable [ ]: enough to see a decrease in prey abundance and not too high to stress the predators themselves 1 L 1 L 1 L 1 L 1 L 1 L Control bottles with only prey to determine prey growth/mortality during experiment Bottles with prey and predator

16 Grazing/Ingestion Rate Experiments Bottles should be filled to the rim with SW & acclimated for 2 hrs before zoop are introduced Water T. has to be maintained as ambient (running a water bath or hanging bottles in the sea) Add zooplankton to incubation bottles using a wide bore pipette Maintain food in suspension by stirring or gentle bubbling (also keep zoop. happy)

17 Grazing Rates Experiments Compute ingestion rate (I), amt. food cop -1 hr -1 I = (C 0 - C t )/n*t C 0 = initial [Chl a] (better to use the final concentration in control bottles!) C t = final [Chl a] n = # of grazers per bottle t = incubation time

18 Gut fluorescence technique I = 24 * G * k 1) 24-hour gut pigment content dynamics 2) Gut evacuation rate 3) Gut pigment degradation gut content (ng pigement Ind. -1) y = e x R 2 = time (min) Pakhomov & Froneman (2004) Collect animals every 4-6 hours Measure individual or community mean gut pigment content Measure gut evacuation rate experiment by monitoring gut pigment decline over time Optional: measure pigment degradation coefficient I = (24 * G * k)/(1-b )

19 Predation rate calculations Can be conducted as in previous slide: Instead of Chl a, measure copepod numbers (added to control and experimental bottles) Instead of copepod grazers, add to experimental bottles chaetognath, a predatory zooplankton

20 Dilution Rate Experiment (Landry & Hassett 1982) Measures grazing rate of microzooplankton assemblage on Chl a (or bacteria) 1. Collect seawater from desired depth (chla maximum is best) 2. Filter a fraction of SW through appropriate size mesh to obtain SW with bulk microzooplankton assemblage and phytoplankton

21 Dilution Rate Experiment 4. Filter the remaining water through a cartridge filter (0.2 μm) to obtain particle free seawater (only nutrients) 5. Create a dilution series, can use 250 ml jars 1* grazing 0.75*grazing 0.50*grazing 0.25 *grazing Grazing pressure decreases with increasing dilution, but NOT growth rate

22 Dilution Rate Experiment 6. Have an initial conditions bottle for each dilution rate 7. Make sure you have reps for each dilution 8. Measure initial [phyto] in each bottle 9. [phyto] can be bulk [chl a] or size fractionated [chl a]

23 Dilution Rate Experiment 10. Incubate bottles for 24 hrs at in situ light and temperature conditions 11. Measure final [phyto] 12. Compute grazing rate In each bottle, phytoplankton grows according to P t = P o * e kt P t = final [phyto] P o = initial [phyto] k = apparent growth rate (hr -1 ) t = incubation time (hr)

24 Dilution Rate Experiment We can compute k for each bottle k = ln e (P t /P o )/t But k is an apparent growth rate k = r - g r = rate of phyto growth (hr -1 ) g = grazing rate (hr -1 ) P t = P o * e (r-g)t

25 The apparent phytoplankton growth rate in your diluted bottles: P t = P o * e (r-1g)t P t = P o * e (r-0.75g)t P t = P o * e (r-0.5g)t P t = P o * e (r-0.25g)t

26 Dilution Rate Experiment Plot k vs. d to determine slope g by linear regression analysis Landry & Hassett 1982 Apparent growth rate d -1 Dilution factor k = r - g*d

27 Dilution Rate Experiment Dilution bottles have same growth rate (r), but different grazing rates (g) depending on dilution. Therefore, apparent growth rate (k) changes according to: Y = intercept Y slope * X k = r - g*d Equation of a line with k = y = apparent growth rate d = dilution factor; x (decimal fraction of unfiltered seawater) r (growth rate) = y-intercept g (grazing coefficient) = slope

28 Obtain rapid, synoptic data on zooplankton distribution through an echosounder An echosounder transmits sounds and receive echoes Acoustics

29 Acoustics Each animal in the water column scatters a wave back Its backscattering depends on its size, shape, internal structure, and material properties Zooplankton scattering is categorized into 3 main groups based on their material properties

30 Acoustics Organism Type Example Echo energy/organism mass (log-scale, db) Fluid-Like Decapod shrimp 24 Pteropod 43 Elasticshelled Gasbearing Siphonophore 24 At an acoustic frequency of 200 Hz

31 Acoustics NEPTUNE is a network of ocean observatory systems moored on the ocean floor in BC Live data is gathered 24/7 and made freely accessible to researchers

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33 Acoustics The echo data is displayed through an echogram A 2D representation of a succession of echo signals Each signal is a single vertically oriented line with the information on backscattering strength encoded by the degree of darkening or colour e.g. of an echogram from NEPTUNE echosounder in Folger Passage

34 Acoustics During data analysis the echo data is allocated to specific scattering classes of organisms Models can be used to convert scatter into an estimate of zooplankton biomass Useful tool to look at diurnal migration of zooplankton Concurrent zooplankton net samples can be carried out to determine to what species the zooplankton backscatter corresponds to

35 Target Strength vs. frequency

36 Scattering 3 different frequency transducers (higher khz pings, bigger target (eg. fish)

37 Acoustic Doppler Current Profiler (ADCP) -Hydroacoustic current meter, like a sonar, to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. -The working frequencies range from 38 khz to several magahertz 4 transducers

38 What you can measure for your Bamfield project (underlined, things that we will be doing together as a group on Mon-Wed) Chlorophyll (total & size-fractionated) (BF) Nutrients (Si, NO 3-, NO 2-, P, and NH 4+ ) (BF) Salinity (BF) Temperature (BF) Oxygen (BF) Light in Water CDOM Turbidity Chlorophyll fluorescence (BF) O 2 evolution & consumption (BF) Phytoplankton identification (BF) & counts using inverted microscope & settling chambers (UBC) Growth rates of bacteria and phytoplankton, sinking rates of phytoplankton and Grazing rates on bacteria and small phytoplankton Bacteria counts using DAPI or Acridine Orange (UBC) Zooplankton identification and counting (BF) Estimate phytoplankton C from phytoplankton counts and estimate of size & volume (BF) Estimate zooplankton C from conversion factors (BF) Estimate bacterial C, from bacteria size estimates and conversion factors (UBC) Distinguished between carnivorous and herbivorous zooplankton (BF) - Wet weight (BF) dry weight (UBC) Predation rates by zooplankton

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