EOSC Biology 2. Zooplankton Measurements

Transcription

1 EOSC Biology 2 Zooplankton Measurements

2 What are zooplankton Plankton = organisms unable to swim against currents. Drifters. (Hensen 1887) Zooplankton = heterotrophic plankton

3 Importance of Zooplankton Hold key position in pelagic food web Transfer energy from phytoplankton to higher trophic levels Affect fish recruitment Mediate the removal of anthropogenic CO 2 into the deep ocean Fuel the benthic community Nano & microzooplankton: key players of microbial loop

4 Zooplankton taxonomic diversity unparalleled in the plankton we may find an assemblage of animals more diverse and more comprehensive than is to be seen in any other realm of life. (Hardy 1965) Size range from 2.0 µm to 200 cm (> 30,000 species)

5 Zooplankton size spectrum Net plankton - 20 µm to 200 cm

6 Holoplankton: spend their entire life as plankton Meroplankton: spend only part of their lifecycle, usually larval stage, as plankton

7 Systematic Overview Protozooplankton-protozoans Flagellate Ciliates Foraminifera Radiolaria Metazooplankton-metazoans (> 20 μm)

8 Cnidaria Siphonophora Hydromedusae Ctenophora (comb jellies) Scyphomedusae

9 Mollusca Heteropoda (swimming snail) Pteropoda (sea slugs or sea angels) Veliger larvae Cephalopoda

10 Chordata Appendicularia Fish larvae Thaliacea (salps) Annelida Chaetognatha Polychaeta Chaetognaths (arrow worm)

11 Crustacea Amphipoda Isopoda Cladocera Euphausiacea Mysidacea Ostracoda (seed shrimp)

12 Crustacea Copepoda Decapoda Cirripidia (barnacle) larvae

13 Echinodermata Echinoderm larvae (starfish, sea urchins, sand dollars, and sea cucumbers)

14 Zooplankton Sampling Problems 1. Zooplankton in highly dynamic environment 2. Hard to sample the same population 3. Fixed station = different zooplankton populations passing by Accompany every plankton sampling program by hydrographic documentation

15 Sampling Design 1. Define purpose of zooplankton scientific study Sampling design will depend on purpose Identify research questions, hypotheses, objectives Example Assessing relationship b/w size & vertical migration vs. determining zooplankton community grazing rate

16 Sampling Design 2. Identify potential dominant processes that affect the zooplankton in study Maybe physical, chemical, biological Supporting information on the environment of zooplankton Collaborative effort between physical, biological, and fisheries oceanographers Examples Hydrography, currents, light, fluorescence, phytoplankton biomass, production, composition, fish distribution

17 Sampling Design 3. Define the temporal and spatial scales these forcing processes are operating at Physical, chemical, biological processes might be occurring at different spatial/temporal scales, & are interlinked This will determine the appropriate scale of investigation

18 Stommel Diagram

19 Sampling Design 4. Prepare a detailed work plan Define sampling locations Determine sampling frequency Establish sampling size (think about statistical analyses of your data) Decide which variables to measure Decide which sampling methods to use

20 Collecting Zooplankton Water bottles - small volume, few L Underway pumping - 10 s L - 10 s m 3 Nets of all shapes and sizes s m 3 Continuous Plankton Recorder (CPR) Laser Optical Plankton Counter (LOPC) Acoustics In situ camera system Research requirements and species of interest dictate the sampling method used

21 Net Sampling Conical OUR Opening-closing net Conical w/ mouth reducing cone Bongo Net Multi Net Conical-cylindrical Closing Net

22 Net Sampling Advantages: low cost, towed from any type of vessel, ease of use E.G. for sampling mesozooplankton, use a conical net: 200 μm pore size net, with an R = 6 & m mouth diameter

23 Cod ends examples

24 Net Sampling Issues Extrusion Avoidance Clogging A given net sample is representative of a limited size range. This is dependent on mesh size and avoidance

25 Extrusion (net escape) Individuals smaller than diameter of mesh opening Water pressure can extrude organisms > mesh opening - Influenced by tow speed (0.7-1 m/s best) - Mesh size of 75% of carapace width of organism, this catches 95% organisms at high speeds of 9-10 m/s (Nichols and Thompson 1991) What minimum size of organism would a 200 µm net catch?

26 Atkinson et al. (2012) macrozooplankton mesozooplankton

27 1 2 3

28 Schindler s sampler simple & cheap near surface and bottom l of water shallow sampling small zooplankton fraction discrete sampling

29 Avoidance Zooplankton can actively swim out of the net path Most serious bias for meso & macrozooplankton Net size dependent Individual escape velocity increases proportionally with net radius and towing speed Few solutions as reaction distance and escape velocities of zooplankton are poorly known

30 Micronekton net avoidance Kaartvedt et al. (2012)

31 To prevent/reduce net avoidance Of visual zooplankton (euphausiids, mysiids, and fish larvae): Sample at night Paint frame and net dull dark colour, such as grey or blue Creation of bow wave in front of net increases net avoidance Obstructions in net mouth lead to avoidance When sampling organisms > 5 mm, use no bridle. E.g. Bongo net OR multi-net Strobe light system (blinding plankton)

32 Clogging Affected by: Density and composition of suspended material Mesh size Net filtration efficiency Shape of net Conical ok, conical cylindrical best for very productive waters

33 Problems associated w/ clogging Water column not sampled uniformly More organisms extruding b. of pressure differences b/w inside and outside of net Significant clogging if filtration efficiency drops below 85%

34 Filtration Efficiency (need no less than 85%) F = ratio b/w actual volume vs. theoretical volume through mouth opening F =V/(A*D) V = volume filtered by the net A = area of net mouth D = Towing distance Depends on R, the ratio b/w the open area of the net mesh VS. area of mouth opening

35 R = ratio of open area of net mesh to area of mouth opening R = (α*β)/a α = total area of net mesh β = porosity, open area fraction of mesh size, from gauze manufacturers, average (~ 0.47) A = mouth area (pi*r 2 ) Note: Porosity ranging from 0.15 for a 20 µm nitex mesh (15% porosity) to 0.6 for a 1000 µm nitex mesh (60% porosity)

36 To avoid clogging, filtration efficiency should be > 85%, and then Recommended R is at least: For oceanic sampling: 3.5 For coastal waters: 6 Smiths, Counts, and Clutter (1968) developed an equation to enable choice of best net design

37 Smiths, Counts, and Clutter (1968) equations: Log 10 R=0.37*Log 10 (V/A) for blue water Log 10 R=0.38*Log 10 (V/A) for green water Where R = ratio of open area of net mesh to area of mouth opening V = volume to be filtered (mouth area X depth of plankton haul) A = mouth area You can use this equation to calculate whether your assumption of R (either 3.5 or 6) was appropriate given your deepest sampling station (ie. 150 m)

38 Volume Filtered Determination To obtain a quantitative estimate of [zooplankton], the volume filtered during a tow must be known Measured by a flowmeter, a propeller that rotates with flow of water and records the number of revolutions

39 Volume Filtered (V) Determination V = (L/F) *A L = length of H 2 0 column, (# revolutions) F = calibration factor (ratio of revolutions per meter), supplied by manufacturer A = net mouth area

40 Measuring filtration efficiency of a net Filtration efficiency (F ) of net can also be computed using flowmeter directly.

41 Measuring filtration efficiency of a net On a calm day 1. Lower the empty net frame w/ flowmeter & haul it back up at usual haul speed. Repeat 5 times and record # of revolutions (this is your N ) 2. Repeat with net attached, and record # of revolutions (this is your N) 1. Calculate F = filtration efficiency = N/N N = avg. # of revolutions with net N = avg. # of revolutions without net 4. This F can then be used to calculate actual volume filtered during plankton haul from F =V/(A*D), so V = F x A x D

42 Flowmeter Flometer should be placed halfway between the center of the net and the frame.

43 Towing paths of a net tow 1. Vertical 2. Deep horizontal 3. Oblique

44 Towing Methods Vertical Ship stationary kg weight Bring up at m/s Horizontal Ship is moving Range of depths and weights Oblique Heavy depressor weight below net Out: ship moving at 2-3 m/s, wire out at 1 m/s In: ship moving at 1m/s, wire in at 1m/s

45 Sampling Considerations If wind > 10 knots, to prevent wire from going under the boat, keep wind on the side of bow you are sampling from When windy, the wire will be at an angle, how do you measure the actual depth of your haul?

46

47 Sample Handling 1. Carefully rinse net with seawater to concentrate every organism in cod end 2. If closing net, rinse only lower part 3. Screw-off cod end to pass specimens into jar ( ml glass or polyethylene) 4. Use filtered seawater to concentrate sample and rinse cod end 5. Label, Pickle 6. Rinse net with freshwater

48 Sample Preservation Use 4 % buffered formalin Concentrated formalin (37-40%) Buffered by Borax Add borax in a ratio of 2 g per 98 ml of 40% formalin This results in a ph of 8.2, suitable for a mixture of zooplankton If too acidic, calcareous shells dissolve If too basic, crustacean and gelatinous tissue is damaged

49 How much formalin would you add to a 500 ml sample?

50 Sampling for Live Zooplankton Handle net, cod end gently Tow upwards at an angle at low speeds, m/s Choose a fine mesh relative to size of organism Avoid direct sunlight or bright deck lights Have filtered seawater at ambient T and S, ready for reception of animals Plastic 4 L jars make optimal containers Use large bore pipettes to transfer organisms from jar into sorting petri dish