Effects of Sediment and Suspended Solids on Freshwater Mussels
Jim Stoeckel School of Fisheries, Aquaculture, and Aquatic Sciences Auburn University Why is sediment a problem? Mussels are adapted to live in sediments
Not all sediments are the same • Firm, stable sediment = GOOD • Unstable or Flocculent sediment = BAD Dislodgement
Mussels sink into sediment Sediments taken in or during filtering Sediments are easily suspended activities Potential Impacts
• Clearance rates tend to decrease
• Pseudofeces production tends to increase
• Feeding
• Spawning How do Bivalves Sort Particles?
Pseudofeces
Sorted by: 1) inorganic vs. organic 2) Nitrogen vs Carbon rich 3) Algal species ?
Site: 1) Gills – maybe 2) Palps – Yes! Feces: Passed Pseudofeces: Rejected particles bound in mucus through 1) “non-food” digestive 2) Excess food system Ingestion: Particles pass into stomach Selection Efficiency Varies Among Species and Habitat
Good
Poor What about unionid mussels? Payne et al. 1995
High TSS LOW TSS
Palp area : Gill area = 3.78 +/- 0.95 Palp area : Gill area = 11.5 +/- 1.3 Two General Causes of High Suspended Solids
Poor land use practices Eutrophication Inorganic: Organic: sand, silt, phytoplankton clay bacteria Eutrophication experiments in a semi-natural setting • Created eutrophication gradient • 6, 0.1 ha ponds South Auburn • 2 – no fertilization Fisheries • 2 – moderate fertilization Research • 2 – high fertilization Station • Monitored weekly – Secchi – Total suspended solids (TSS) • Organic and Inorganic 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 Effect on clearance rate
Air pump Clearance rate declined with increasing TSS Does this mean reduced feeding and growth? 0.030 Particle removal rate remained constant effect likely dependent on ability to sort 0.025 food from non food (gill:palp ratio) R2 = 0.52 0.020 Particle removal rate = 0.085 mg/g/hr
0.015 0.11 mg/g/hr
0.010
Clearance rate (L/g/h) rate Clearance 0.005 0.10 mg/g/hr
0.000
0 10 20 30 40 50 60
>1.5 m Total suspended solids (mg/L) ~ 0.2 m Landis et al. (2013) Effect on Growth ? • Suspended pocket nets in ponds • Avoid potential pedal feeding • TSS = available food resources
Air lift No significant trend in growth Landis et al. (2013) (April 17 – Nov 11)
0 10 20 30 40 50
Mean total suspended solids (mg/L)
~ 0.2 m What about reproduction?
Spermatozeugmata
What happens at high TSS? • Selectivity breaks down? • Sperm bound up with pseuodofeces? Lack of effect on growth suggests selectivity and pseudofeces not major factors However….
0.030 Smaller volume of water cleared of particles per unit time
0.025 • Reduced ability to “collect” spermatozeugmata? R2 = 0.52 • Reduced fertilization of females? 0.020
0.015
0.010
Clearance rate (L/g/h) rate Clearance 0.005
0.000
0 10 20 30 40 50 60 Total suspended solids (mg/L)
Landis et al. (2013) Gravid female No glochidia
• All or nothing fertilization: if • Rapid decline in proportion gravid, nearly 100% of eggs in gravid females with gills were fertilized 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 n = 7 ponds Inorganic solids – carp In-pond raceway n = 2 ponds Provide constant aeration
Air lift High TSS pond Low TSS pond (mean ~80 mg/L) (mean ~1 mg/L) Organics Inorganics
O:I 5.7 1.2 4.5 1.5 1 0.3 0.3
• No significant decrease in growth with increasing TSS and declining O:I ratio
• Decrease in growth at low TSS
~~ 0.1 0.1 m m
Landis et al. (2016) Reproduction? 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 Methods – L. subrostrata
Gill extracts 22 gauge needle 3 categories Empty Fertilized eggs invert-embryo.blogspot.com Glochidia
Tyler Mosley Fertilized eggs 1.0 October Glochidia 1.0 0.8 0.5 0.6 0.0 1 6 10 11 12 77 80 Average TSS (mg/L)
0.4 brood type Proportion Fisher’s exact test 0.2 for proportions
Proportion females fertilized females Proportion 0.0 Z = -4.1; p = 0.00 0 20 40 60 80 100 1.0 November TSS (mg/L) 0.6 0.8 B B 0.5 B B B B 0.60.4
0.3 0.4 0.2 A 0.20.1
0.00.0 Proprotion massProprotion increase
Proportion of females with glochidia with females of Proportion -0.1 0 20 40 60 80 100 1 6 TSS9 10(mg/L)11 78 80 Landis et al. (2016) Average TSS (mg/L) Fertilization at high TSS appears interrupted but not glochidia development
Glochidia
1.0
0.5
1.0 0.0 November 1 6 10 11 12 77 80 Average TSS (mg/L) 0.8 brood type Proportion
0.6
0.4
0.2
0.0 Fisher’s exact test
Proportion of females with glochidia with females of Proportion 0 20 40 60 80 100 for proportions TSS (mg/L) Landis et al. (2016) Z = -4.3; p = 0.00 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 1.0 Results: 0.8 R. ebenus 0.6 R2 = 0.02 0.4 p = 0.78 0.2 eggs or glochidia 0.0
Proportion with fertilized Proportion 0 20 40 60 80 100 1.0Total suspended sediments (mg/L) 0.8 No apparent decline 0.6 R2 = 0.56 p = 0.05 in fertilization but 0.4 decline in glochidia 0.2 production with 0.0 increased TSS with glochidiaProportion 0 20 40 60 80 100 Total suspended sediments (mg/L) Landis et al. (2016) ~ 0.1 m What is impact on recruitment?
Conducted “accidental” study Experimental design Mussels and fish added to 12 ponds in December
Host: 200 Bluegill / pond
No Herbicide X 4 ponds
Low Herbicide (0.2 mg/L) X 4 ponds
Ligumia subrostrata:
11 gravid females / High Herbicide (2.0 mg/L) X 4 ponds pond Drained ponds in November and harvested YOY recruits. Mussels harvested from Ponds in the November 2013 • YOY had grown to large size by November Relatively easy to find (30 – 60 mm) Number recruits per pond 100 150 200 50 0 Young Yearof Mussels Control Roundup© treatment Low High reduced recruitment. 1) No evidencethat herbicide factorherbicide than other treatments,suggesting driving 2) Recruitmentvariablein all (ANOVA, TSS ? p = 0.947) = • Treatment affected terrestrial vegetation on pond sides High Dose Pond
35 (ANOVA, p=0.238) 30
25 Medium Dose Pond
20 TSS (mg/L) TSS 15
10 Control Low High Roundup © treatment Control Pond • No impact on Total Suspended Solids Negative relationship between recruitment and TSS
200 l 150
100
50 # Recruits pondper # Recruits
0 10 15 20 25 30 35 TSS (mg/L) March-October Conclusions
Results similar regardless of TSS type
• Concentration is important
• Organic vs inorganic less important • Reproduction seems to be more sensitive than growth • Reproduction > 20 mg/L; Growth > 80+ mg/L • 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 Current Research: Mechanism(s) Behind Reduced Clearance Rates Current Study on Texas Mussels
• What concentration initiates closure?
• How long do they stay closed?
Spermatozeugmata No gamete aquisition Food Little/no feeding Oxygen waste Anaerobic respiration Closed Open
TSS?? 16 14 12 10 8
TSS (mg/L) 6 4 2 0 MosselMonitor 0 2 4 6 8 10 12 14 16 18 20 Time (hr) Previous Funding Current Funding AAES – HATCH program Texas Office of the Comptroller
USFS Center for Bottomland Texas State Hardwoods Research University
Tyler Mosley Michael Hart Andrew Gascho-Landis Brad Staton
Ryan Fluharty Wendell Haag Allen Pattillo Daniel (Square) Foree