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