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Effects of Sediment and Suspended Solids on Freshwater Mussels
Jim StoeckelSchool of Fisheries, Aquaculture, and Aquatic Sciences
Auburn University
Why is sediment a problem?
• Firm, stable sediment = GOOD
Mussels are adapted to live in sediments
• Unstable or Flocculent sediment = BADDislodgement
Mussels sink into sedimentor
Sediments are easily suspended
Sediments taken in during filtering activities
Not all sediments are the same
Potential Impacts
• Clearance rates tend to decrease
• Pseudofeces production tends to increase
• Feeding
• Spawning
How do Bivalves Sort Particles?
Site: 1) Gills – maybe2) Palps – Yes!
Sorted by:1) inorganic vs. organic2) Nitrogen vs Carbon rich3) Algal species ?
Ingestion: Particles pass into stomach
Pseudofeces: Rejected particles bound in mucus1) “non-food”2) Excess food
Pseudofeces
Feces:Passed through digestive system
Selection Efficiency Varies Among Species and Habitat
Poor
Good
What about unionid mussels?
Palp area : Gill area = 11.5 +/- 1.3Palp area : Gill area = 3.78 +/- 0.95
Payne et al. 1995
LOW TSS High TSS
Two General Causes of High Suspended Solids
Organic:phytoplanktonbacteria
Inorganic:sand, silt,
clay
Eutrophication
Poor land use practices
Eutrophication experiments in a semi-natural setting
• Created eutrophication gradient• 6, 0.1 ha ponds• 2 – no fertilization• 2 – moderate fertilization• 2 – high fertilization• Monitored weekly
– Secchi– Total suspended solids (TSS)
• Organic and Inorganic
South AuburnFisheries Research Station
Experimental mussel
• Ligumia subrostrata – lentic species• Age – 1 individuals• 38 mussels/pond• Sex ratio 1 : 2.4 (male : female)• Tagged individuals• Recorded length and weight • April 27 – November 11, 2010
Air pump
Effect on clearance rate
Total suspended solids (mg/L)
0 10 20 30 40 50 60
Cle
aran
ce ra
te (L
/g/h
)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Clearance rate declined with increasing TSS
R2 = 0.52
Does this mean reduced feeding and growth?
0.11 mg/g/hr
0.10 mg/g/hr
Particle removal rate = 0.085 mg/g/hr
Particle removal rate remained constanteffect likely dependent on ability to sort food from non food (gill:palp ratio)
~ 0.2 m>1.5 m
Landis et al. (2013)
• Suspended pocket nets in ponds• Avoid potential pedal feeding• TSS = available food resources
Effect on Growth ?
Air lift
No significant trend in growth (April 17 – Nov 11)
10 20 30 40 500
Mean total suspended solids (mg/L)
~ 0.2 m
Landis et al. (2013)
Spermatozeugmata
What happens at high TSS?• Selectivity breaks down?• Sperm bound up with pseuodofeces?
What about reproduction?
Lack of effect on growth suggests selectivity and pseudofeces not major factors
Total suspended solids (mg/L)
0 10 20 30 40 50 60
Cle
aran
ce ra
te (L
/g/h
)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
R2 = 0.52
Smaller volume of water cleared of particles per unit time
• Reduced ability to “collect” spermatozeugmata?
• Reduced fertilization of females?
However….
Landis et al. (2013)
• All or nothing fertilization: if gravid, nearly 100% of eggs in gills were fertilized
Gravid female No glochidia
• Rapid decline in proportion gravid females with increasing TSS
Landis et al. (2013)
What about inorganics: sand, silt, clay
• No effect on growth
• Negative impact on proportion gravid
Methods – Ligumia subrostrata
L. subrostrata – lentic, long-term brooders Sexually dimorphic
15 females : 12 males/pond Growth
2 yr old mussels August - November
Methods – Pond set up
7, 0.1 ha ponds Inorganic solids – carp In-pond raceway Provide constant aeration
Air lift
n = 7 ponds
n = 2 ponds
High TSS pond(mean ~80 mg/L) Low TSS pond
(mean ~1 mg/L)
5.7O:I 1.2 4.5 1.5 1 0.3 0.3
• No significant decrease in growth with increasing TSS and declining O:I ratio
InorganicsOrganics
• Decrease in growth at low TSS
~ 0.1 m~ 0.1 m
Landis et al. (2016)
Methods – Ligumia subrostrata
15 females : 12 males/pond Proportion of females with fertilized
eggs or glochidia/pond Examined gills 2 times October 11 and November 15
Reproduction?
Methods – L. subrostrata
Gill extracts 22 gauge needle 3 categories
Empty Fertilized eggs Glochidia invert-embryo.blogspot.com
Tyler Mosley
October
TSS (mg/L)0 20 40 60 80 100
Prop
ortio
n fe
mal
es fe
rtiliz
ed
0.0
0.2
0.4
0.6
0.8
1.0
November
TSS (mg/L)0 20 40 60 80 100Pr
opor
tion
of fe
mal
es w
ith g
loch
idia
0.0
0.2
0.4
0.6
0.8
1.0
Average TSS (mg/L)Prop
ortio
n br
ood
type
0.0
0.5
1.0
Fertilized eggsGlochidia
1 10 11 12 77 806
Fisher’s exact test for proportions
Z = -4.1; p = 0.00
Average TSS (mg/L)
Prop
rotio
n m
ass
incr
ease
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1 6 9 10 11 78 80
A
BB
B BB
B
Landis et al. (2016)
November
TSS (mg/L)0 20 40 60 80 100Pr
opor
tion
of fe
mal
es w
ith g
loch
idia
0.0
0.2
0.4
0.6
0.8
1.0
Fisher’s exact test for proportions
Z = -4.3; p = 0.00
Average TSS (mg/L)Prop
ortio
n br
ood
type
0.0
0.5
1.0
Glochidia
1 10 11 12 77 806
Fertilization at high TSS appears interrupted but notglochidia development
Landis et al. (2016)
Is reproduction inhibited in a riverine species?
R. ebenus – lotic, short-term brooder Gamete extract to determine sexes
15 females : 12 males/pond Dates: Mar. 15 to June 7 Proportion of females with
fertilized eggs or glochidia Gill extracts 4 times -
May 20, 26, 30, and June 7
Total suspended sediments (mg/L)0 20 40 60 80 100Prop
ortio
n w
ith fe
rtiliz
ed
eggs
or g
loch
idia
0.0
0.2
0.4
0.6
0.8
1.0
R2 = 0.02p = 0.78
Total suspended sediments (mg/L)0 20 40 60 80 100Pr
opor
tion
with
glo
chid
ia
0.0
0.2
0.4
0.6
0.8
1.0
R2 = 0.56p = 0.05
Results: R. ebenus
No apparent declinein fertilization but decline in glochidiaproduction with increased TSS
~ 0.1 mLandis et al. (2016)
What is impact on recruitment?
Conducted “accidental” study
Host: 200 Bluegill / pond
Experimental design
No Herbicide
Low Herbicide (0.2 mg/L)
High Herbicide (2.0 mg/L)11 gravid females / pond
X 4 ponds
X 4 ponds
X 4 ponds
Ligumia subrostrata:
Mussels and fish added to 12 ponds in December
Mussels harvested from Ponds in the November 2013Drained ponds in November and harvested YOY recruits.
• YOY had grown to large size by NovemberRelatively easy to find (30 – 60 mm)
Num
ber r
ecru
its p
er p
ond
0
50
100
150
200
Young of Year Mussels
2) Recruitment variable in all treatments, suggesting drivingfactor other than herbicide
1) No evidence that herbicide reduced recruitment.
(ANOVA, p = 0.947)
TSS ?
Control Low High
Roundup © treatment
High Dose Pond
Control Pond
Medium Dose Pond
• Treatment affected terrestrial vegetation on pond sides
• No impact on Total Suspended Solids
TSS
(mg/
L)
10
15
20
25
30
35
Control Low High
Roundup © treatment
(ANOVA, p=0.238)
TSS (mg/L)10 15 20 25 30 35
0
50
100
150
200
Negative relationship between recruitment and TSS#
Recr
uits
per
pon
d
March-October
l
ConclusionsResults similar regardless of TSS type
• Concentration is important
• Organic vs inorganic less important
• Reproduction seems to be more sensitive than growth
• Mechanism may vary among species
• Fertilization bottleneck likely driven by reduced clearance rate
• Glochidial bottleneck likely driven by…??...respiration???
• Palp:Gill ratios may be a valuable tool• Identify species and/or populations at greatest risk
• Predict problematic TSS concentrations
• Reproduction > 20 mg/L; Growth > 80+ mg/L
Current Research: Mechanism(s) Behind Reduced Clearance Rates
Current Study on Texas Mussels
FoodOxygen waste
OpenClosed
TSS??
Little/no feedingAnaerobic respiration
• What concentration initiates closure?
• How long do they stay closed?
Spermatozeugmata No gamete aquisition
MosselMonitor 0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12 14 16 18 20
TSS
(mg/
L)
Time (hr)
AAES – HATCH program
Andrew Gascho-Landis Brad Staton
Allen Pattillo Daniel (Square) Foree
USFS Center for Bottomland Hardwoods Research
Previous Funding Current FundingTexas Office of the Comptroller
Texas State University
Tyler MosleyMichael Hart
Wendell HaagRyan Fluharty