mussel mediation of nutrient availability and algal composition 1.how do dreissenid mussels affect...
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Mussel mediation of nutrient availabilityand algal composition
1.How do dreissenid mussels affect phosphorus (P) availability? 2. How do they affect seston composition?
Core team members and responsibilities:Tom and Hank—overall design Jim Liebig—setup of feeding experiments and data analysisAshley Burtner and Danna Palladino—nutrient excretion experiments
and nutrient, chlorophyll analysesHuijuan Tang—phytoplankton analysesPeter Lavrentyev—mussel and microbial food web interactions
Analytic and lab assistance:Nancy Morehead, Dave Fanslow, and Joann Cavaletto
This means: We are looking at what dreissenid mussels do
Where have we been (previous results): mussel P excretion is sensitive to seston N:P ratio and P
ingested (A)
R = -0.726
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 10 20 30 40 50Seston N:P (molar)
P e
xcre
tio
n (
ug
mg
-1 h
-1) R = 0.754
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 0.0002 0.0004 0.0006 0.0008A (ugP mg-1 h-1)
P e
xcre
tio
n (
ug
mg
-1 h
-1)
Results from experimentally manipulated mesocosms on Gull Lake
Proposed Activities for 2010What we said last year
Jan – Feb: continue lab experiments. Work-out cultures, P-content, and bioassay approach. Work of available-P chemical assay’s for riverine material.
Four Sets of Experiments (Mar – May – July – Sept)
• determine phosphate and ammonia excretion rates by dreissenids as a function of seston composition, feeding rate, and temperature
• estimate the amount of P and N that dreissenids biodeposit each in feces and in pseudofeces as a function of seston composition, feeding rate and temperature
• determine if mussel tissue and shells are sink for P
• evaluate the availability of the P in feces and pseudofeces
• evaluate the availability of the P in riverine material (before and after exposure to mussels)
Where we are—what we did and where we are with analysis
Challenges (of experiments from hell):• Getting mass balance on nutrients and
everything measured• Cannot easily separate feces from
pseudofeces or other settled material• Feces and pseudofeces are fragile—cannot
screen to separate.• Getting enough biodeposits for assay
experiments
Typical experimental set-up, but…
Photo by Cathy Darnell
Control beakers and treatment beakers containing quagga mussels filled with Control beakers and treatment beakers containing quagga mussels filled with feeding suspension. Bubblers keep suspension mixed.feeding suspension. Bubblers keep suspension mixed.
…we didn’t collect enough biodeposits for bioassay
So we used big 20-L buckets, lots of mussels, and brought lots of water (~300L) back to lab for acclimation and experiments
Tom siphoning experimental bucketsto separate water-column water from bottom deposits
Sampling of buckets to achieve mass balance
For each of 2-3 control buckets and 4 experimental buckets we sampled water:
• Initial sample of bucket contents
• Water column sample at end of experiment
• Water with settled material in bottom of bucket
What we sampled in buckets
All experiments (May (2), July, Sept., Dec.)
• Chlorophyll
• Phytoplankton
• Particulate P
• Particulate N and C
• Total suspended solids (initial only)
• Preliminary experiment:
• Microzooplankton and MFW (bacteria)
A few results—samples still in analysis
• Estimates of clearance rates based on chlorophyll and phytoplankton analysis
• A few results from excretion experiments• P in mussel tissue and shells• Microzooplankton grazing and
demonstration experiment on effects of mussels on MFW using FlowCam and fluorescence microscopy (Peter Lavrentyev)
Date Temp(oC)
Initial chl (µg/L)
F-gross(mL/cm2/h)
F-net (mL/cm2/h)
P excretion (µg/mg/h)
Dominant alga
7 May 13 1.37 23.26 ± 1.17 8.91 ± 2.96 0.00221 Cyclotella
27 May 23 0.77 82.55 ± 2.75 24.82 ± 7.13 0.0125 Cyclotella
2 July 20 6.50 40.10± 1.89 21.89 ± 5.23 0.000127 Fragilaria
23 Sept 19 5.62 19.82 ± 3.20 26.33 ± 2.93 In analysis Microcystis
1 Dec 5 8.01 30.43 ± 1.83 12.76 ± 1.83 In analysis Melosira
Mussels process more than they ingest and excretion rate of P does not relate conveniently to filtering or ingestion rate
Species matters: Net clearance rates of mussels on different algae during July and September 2010
Chroococcus Fragilaria Melosira MicrocystisInitial water 0.005 0.525 0.044 0.030
Feces/pseudofeces 0.017 0.052 0.005 0.142Ratio 3.372 0.099 0.120 4.701
Relative ratio 34.0606 1.000 1.2121 47.4848
Rejection potential indicated by ratio of algal concentration (µgC/L) found in excretion water compared to initial concentration in water animals fed on
Len Total P Content
Date Sample Descrip mm Tissue Shell Tissue Shell Tissue Shell
8/10/2004 L. Erie 3M Zebra Mussels (ZM) 14.30 10.40 0.07960 10.26 117.8 0.1067 0.00938
8/10/2004 L. Erie 3M Quagga Mussels (QM) 14.15 10.55 0.10210 10.23 89.5 0.1079 0.00914
9/5/2008 L. Mi M45 QM-Profunda Large 24.89 3.14 0.02522 24.42 335.4 0.0767 0.00846
9/5/2008 L. Mi M45 QM-Profunda Medium 20.36 3.01 0.02230 13.69 187.8 0.0412 0.00419
9/5/2008 L. Mi M45 QM-Profunda Small 15.38 2.98 0.02770 5.92 78.8 0.0176 0.00218
7/9/2009 Sag Bay Sta 5 QM 24.98 8.98 0.02910 39.26 557.4 0.3525 0.00114
P Conc. (µg/mg) Dry Wt (mg)
P Concentration (µg/mg dry wt) and Total Amount of P (mg/individual) in Mussel Tissue and Shells
Mussel tissue and shell P concentration vary among sites and ~90% of P is in tissues
Lower food web dynamics are driven by microzooplankton and mussels and their
interactions• Using dilution technique, Peter demonstrated
that microzooplankton (primarily protozoans) remove 63% of phytoplankton production/day including medium size algae and some Microcystis
• Preliminary experiment showed mussels feed on whole MFW including bacteria and especially microzooplankton
Tools used: FlowCam and epifluorescence and DIC optics in standard and inverted microscopes
Where we’d like to go(with the help of Peter)
Parallel experiments:• Look at mussel feeding on all seston components (MFW, detritus,
phytoplankton) in beakers in lab using state-of-art methods including flow cytometer, FlowCam and good inverted and standard microscopes
• Relate excretion to feeding• In ship-based/shore-based experiments expose acclimated mussels
to large quantity of water to generate lots of biodeposits for bioavailability experiments (use same mussels and water source for lab experiments)
• Experiments with lab cultures to nail down basics• Other ideas—let the modelers tell us what they want