Mussel mediation of nutrient availability and 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 analysis Ashley Burtner and Danna Palladino—nutrient excretion experiments and nutrient, chlorophyll analyses Huijuan Tang—phytoplankton analyses Peter 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) Results from experimentally manipulated mesocosms on Gull Lake

Proposed Activities for 2010 What 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 feeding suspension. Bubblers keep suspension mixed. Control beakers and treatment beakers containing quagga mussels filled with 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 buckets to 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 ( o C) Initial chl (µg/L) F-gross (mL/cm 2 /h) F-net (mL/cm 2 /h) P excretion (µg/mg/h) Dominant alga 7 May ± ± Cyclotella 27 May ± ± Cyclotella 2 July ± ± Fragilaria 23 Sept ± ± 2.93 In analysisMicrocystis 1 Dec ± ± 1.83In analysisMelosira 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

ChroococcusFragilariaMelosiraMicrocystis Initial water Feces/pseudofeces Ratio Relative ratio Rejection potential indicated by ratio of algal concentration (µgC/L) found in excretion water compared to initial concentration in water animals fed on

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