Freshwater Clams
for
Micro-Filtering
Stormwater
Retention Ponds
Ernie Franke
[email protected]
August 2015
Removing Nutrients from Stormwater Retention Ponds
•Stormwater Ponds Constructed to Control Flooding and Fluctuations in Run-Off
•Today, with Threat of Red-Tide in our Gulf and the Rampant Use of Fertilizers in
an Urban Environment, Emphasis Has Switched to the Task of Removing
Nutrients before Entering the Estuary
•Freshwater Clams, the Size of a Fingernail, Have Been Shown to Decrease
Nutrient Level in Stormwater Bodies by Micro-Filtering the Sediment
•Removal of These Nutrients Decreases Algae Blooms
–Freshwater Clams Multiply Rapidly to Perform a Mass Filtering of Bottom
Sediment
•Dilemma Exists Between Using Chemicals for Algae Control and a Chemical-Free
Approach Using Freshwater Clams to Remove Nutrients
•Popular Copper-Based Herbicides Accumulate in the Sediment of Stormwater
Ponds, Which Unfortunately Kill the Freshwater Clams
•Freshwater Clams Have Invaded All of Florida
–Represent an Economic Threat to the Cooling Pipes of Power Plants, But Pose
No Threat to Stormwater Retention Ponds
–These Clams Aren't Found in Most Stormwater Retention Ponds Because
Copper-Sulfate Is Used to Kill Algae, and Freshwater Clams Cannot Survive
•Tragic Result Is That the Nutrient Level of the Chemically-Treated Stormwater
Pond Remains High
•The Addition of Freshwater Clams to Your Retention Pond Will Not Magically
Cure Your Algae Problem
•Asian Clams Are Merely a Tool in the Integrated Pond Maintenance Tool-Box
We have successfully used Asian clams to micro-filter six stormwater
retention ponds to remove nutrients and decrease algae growth.
2
Asian Paradox
•If You Use Chemicals to Remove Algae from Your Stormwater Retention
Pond, You Probably Don’t Have Asian Clams
•If You Maintain Your Retention Pond Manually (Chemical-Free), Then You
Probably Already Have Invasive Asian Clams
•However, If You’ve Used Chemicals in the Past, and Have Now Switched
to Chemical-Free, Then You May Need to Re-Introduce Asian Clams to
Your Stormwater Pond
•Freshwater Clams Will Then Begin to Multiply and Micro-Filter Your Pond
of Nutrients
If a stormwater retention pond has been maintained manually
(close observation of the muck) and
chemical-free (not lethal to sensitive mollusks),
the invasive freshwater clam is probably already present.
3
Value of Freshwater Clams
•Removal of Nutrients Is a Principal Task of Stormwater Ponds
•Freshwater Clams Provide Micro-Filtering
–Filter Out Nutrients
–Multiply Rapidly in Rich Muck on Bottom of Pond
–No Chemicals Involved
•In the Potomac River, Asian Clam Has Shown a Substantial Decrease in
Phytoplankton and in Water Turbidity (1,2)
•Nuisance to Cooling Water Intake to Power Plant Cooling
–Not a Nuisance for Stormwater Retention Ponds
•They’re Probably in Your Adjacent Lake or Pond Already
–Dig into Top 3” of Muck and See If Present
–If Chemicals Are Used to Control Weeds in Pond, Clams Probably Not Present
•Dilemma:
–Choose between Chemical and Biological Control of Algae
•Chemical Control of Algae
–Copper-Sulfate Additives Effectively Kill Algae
–Copper-Sulfate Also Kills Freshwater Clams
•Manual Control of Algae
–Fresh-Water Clams Micro-Filter Nutrients
–Chemical-Free Approach to Algae Control
•Chemical Approach to Controlling Algae Kills Freshwater Clams
–Anti-Algae Copper-Sulfate Also Kills Fresh-Water Clams
1. Cohen, R.H., (1984), The effect of the Asiatic clam, Corbicula Jluminea, on phytoplankton of the Potomac River, MD., Limnology and Oceanography, Jan. 1984, vol.49, pp 170-180.
2. Phelps, H. L. (1994), The Asiatic clam (Corbicula fluminea) invasion and system-level ecological change in the Potomac River Estuary near Washington, D.C., Estuaries, vol. 17, pp
614–621.
The chemical approach for controlling algae works against
the nutrient-removing features of freshwater clams.
4
Copper Sulfate (Chemical Control) of Algae
•Copper Sulfate Used as Herbicide
–Most Species of Algae Controlled with Very Low Concentrations
–Used In Swimming Pools as an Algicide
•Inhibits Growth of Bacteria, Such as Escherichia Coli
–Copper Ions Are Highly Toxic to Fish, So Care Must Taken with Dosage
•Dilute Solution Used to Treat Aquarium Fish for Parasitic Infections
–Also Used to Remove Snails from Aquariums
•Indicates Toxic Nature of Copper Sulphate
•Over Time, Use Can Increase the Frequency and Severity of Algae Blooms
–Copper Sulfate Quickly Falls thru the Water Column
•Contact Herbicide, Algae Only Killed on the Day It Is Applied
•Accumulates Within Bottom Sediment Layer as a Heavy Metal Precipitate
•Once a Build-Up of Copper Sulfate Begins, a Sterile Lake Bottom Results
•Invertebrates Are Killed Off
–Includes Insects and Their Larvae, Crayfish and Beneficial Bacteria
Populations, Which Inadvertently Weakens the Food Chain
–Noticeable Decline in Forage Fish (fathead minnows for example)
–Poor Body Condition in Game fish and Overall Reduction in Growth Rates
•Conclusions About Copper Sulfate:
–Short-Term Effectiveness, Often Misused and Overused
–Remains in the Pond and Does Not Bio-Degrade
–Can Be Toxic to Fish and Other Organisms
–Results in Copper Build-Up in Pond Sediments
–Creates a Sterile Bottom in the Stormwater Pond
–Kills Beneficial Bacteria
One can easily determine if a stormwater retention pond is maintained
chemical-free by digging into the muck searching for Asian clams.
5
What Do Freshwater Clams Look Like?
Stocking Fresh-Water Clams
The Corbicula fluminea (Asian clam) has a yellowish brown to black shell
with concentric, evenly spaced ridges on the shell surface,
and is about the size of a fingernail.
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Density of Clams in a Shovel-Full
(Shows Both Tan and Black Shells)
Shows Layer of Muck on Top of
Sandy Bottom
Freshwater clams filter phytoplankton and other particles suspended
in the water that are important food sources for algae.
7
Close-Up of Clams
Inside Shell;
Showing White with a Blue-Purple Tint
In the same pond, one sees tan shells,
along with dark brown shells, all with white peaks.
8
Florida's Freshwater Mussels and Clams
http://www.fws.gov/panamacity/resources/Mussel%20harvest%20pamphlet%20March%202008.pdf
•More than 60 Species of Mussels and Clams Live in Florida’s Freshwaters
•Asia Clam (Corbicula fluminea) Common Throughout All Florida
•Florida FWC Does Not Restrict Its Harvest
•Usually Inhabit Shallow, Sandy Bottoms of Lakes and Streams
•Important Functional Component of Freshwater Ecosystems
•Filter / Feeding Activity Cleanses Water by Removing Bacteria, Algae, and
Organic Material
•Sold in Aquarium Trade, Where They Are Known as “Pygmy" or “Gold" Clams
–Used to Clean Aquariums and Remove Algae
•Colonies Serve as Indicators of Water Quality and Overall Health of Aquatic
Ecosystems
•Important Food Source for Many Fish, Birds and Mammals
•Mussels and Clams Affected by Poor Environmental Conditions
•Four Prominent Species Found in Central Florida
–Asian Clam (Corbicula fluminea)
–Fingernail or Pea Clam (Family: Sphaeriidae) Native Specie
–Atlantic Rangia (Rangia cuneata)
–Carolina Marshclam (Polymesoda caroliniana)
•Freshwater Clam Family Tree
–Marine Bivalves Have Independently Invaded Freshwater Many Times
–Today, We Have the Sphaeriidae (fingernail clams) and Corbiculidae (Asian
clam)
Exact identification of the freshwater clam is not essential for its role
of micro-filtering nutrients in the stormwater pond.
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Wading Birds and the Asian Clam (fieldnotes-steve.blogspot.com)
•Photonaturalist Steven Scott, Based in Punta Gorda, FL
(Charlotte County), Documents Flora and Fauna in the
Country, Suburbs and Cities
•Limpkin (Aramus guarauna) Is a Tropical Wading Bird
–Florida Is Northern Limit of Its Traditional Range
–Hunted to Near Extinction in Early 20th Century
–Limpkin Has Made a Remarkable Comeback
•Many Books, Websites and Field Guides Cite That
Limpkins Feed Almost Exclusively on Apple
Snails (Pomacea spp)
–This Pair Has Been Eating Asian Clams
–Apple Snails Are a Native-Florida Species
–Asian Clam Is Exotic and Invasive
This pair of rare limpkins has been busy digging Asian clams
out of the muddy shallows, as evidenced by the banks
of the canal being littered with dozens of shells.
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Diagram of Freshwater Mollusks
Phylum
Class
Mollusca (clams, snails, squids, and relatives)
Gastropoda
Bivalvia (clams, mussels)
(snails and slugs)
Sub-Class
Paleoheterodonta
Heterondonta
Order
Veneroida
Corbiculacea
Sub-Order
Super-Family
Dreissenoidea
Family
Dreissenidae
Genus
Musculium
Specie
(zebra and quagga
mussels)
Corbiculoidea
Sphaeriidae
(fingernail clams, pea
clams or pill clams)
Pisidium
Sphaerium
Corbiculidae
(basket clams)
Corbicula
Corbicula
fluminea
(Asian clams)
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Asian Clam (Corbicula fluminea) and
Fingernail or Pea Clam (Family Sphaeriidae)
The Fingernail or “Pea” Clam is about
half the size of the Asian Clam.
United States Fish and Wildlife Service, Mussel Harvest Pamphlet, March 2008 (United States Fish and Wildlife Service
(http://www.fws.gov/panamacity/resources/Mussel%20harvest%20pamphlet%20March%202008.pdf)
Both the Asian Clam, non-native, and the Fingernail Clam, native,
are found all over Florida.
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2015 U.S. Geological Survey (USCS)
Southeast Ecological Science Center
Asian Clam (Corbicula fluminea)
100% Coverage
of Florida in 2015
The Asian clam covers the entire state of Florida, and most of the Southeast.
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World-Wide Distribution of Asian Clams
(http://www.discoverlife.org/nh/maps/Mollusca/Bivalvia/Corbiculidae/Corbicula/map_of_Corbicula_fluminea.jpg)
The Asian clam covers the entire earth, starting from Southeast Asia.
14
Invasion of Asian Clams (Corbicula fluminea)
50% Coverage of
Florida in 1999
1999
Gradual Increase
in 2001
2001
1999
2011
2012
The USGS has shown the invasion of the Asian clam over the last fifteen years.
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U.S. Geological Survey (USCS)
Southeast Ecological Science Center
•South Florida Hosts a Wide Variety of Non-Indigenous Species
–More Than Any Other Drainage in Florida
–Many Have Become Established in This Disturbed Habitat
•Example: Asian Clam (Corbicula fluminea)
–Came to North America from China in the 1920s
•First Records Are from the Columbia River Basin in the Pacific
Northwest
–Later Established in Southeast Florida
–Maximum Length about 35 mm (1-3/8”) and lives about 3 years
–Known Mostly as a Bio-Fouler of Many Electrical and Nuclear Power
Plants
•As Water Is Drawn from Rivers, Streams and Reservoirs for Cooling,
So Are Corbicula Larvae
•Can Clog Condenser Tubes, Raw Service Water Pipes, and FireFighting Equipment
•Economic Problems Result from Decreased Efficiency of Energy
Generation
•Asian Clam Is Not a Problem for Stormwater Retention Ponds
Warm-water effluents at power plants make a hospitable environment
for stabilizing populations of freshwater clams.
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Freshwater Clams Are Filter-Feeders
•Fingernail Clams Are Mud-Dwellers
–If You Scoop the Bottom of Most Soft-Bottomed Pond or Lake, You’re
Bound to Come Up with Some Freshwater Clams
–Happiest in Still Waters
–Prefer Substrates of Sand, Mud and Clay
–Tiny (most are less than ½”)
•All Clams Have Two Tubes on the Top of Their “Foot"
–One Tube Sucks in Water Containing Food and Oxygen
•Filter-Feeders of Water Taken in Through Siphon
–Take In Oxygen and Very Small Pieces of Organic Matter
–Mini-Plankton and Tiny Pieces of Organic Material
–Other Tube Shoots Out the Clam's Waste
•Like Its Bigger Cousin, It Filters Bits of Organic Debris from the Water
•Life Cycle:
–Self-Fertilizing; Both Male and Female Reproductive Organs
–Young Brooded in the Gills and Released Fully-Formed
–Lives One to Three Years
•Hermaphrodites (both genders in same body) with Internal Fertilization
•Significantly Lowers Nitrite Levels
Corbicula Clam with Siphons and Foot
Visible Protruding from the Shell
The Freshwater Clam is a living filter that many people
use to keep their aquarium water clear and clean.
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Invasive, Non-Native Asian Clam (Corbicula fluminea)
•Additional Common Names
–Prosperity Clam, Pygmy Clam, Golden Clam and Good Luck Clam
•Origin and Spread
–Native to Fresh Waters of Eastern and Southern Asia
–First discovered in 1938 in Washington State
–Initially Assumed Imported as Food Source for Immigrating Chinese
–Quickly Spread Across the Continent
–Currently Found in 44 states
•“Corbicula" (little basket) Refers to Concentrically-Ribbed Shells and General
Shape
•Reproduces in Large Colonies That Can Clog Waterways and Pipes
•Widespread Throughout Freshwater and Some Estuarine Habitats in U.S.
•Factors That Contribute to Its Establishment and Spread
–Reproduces Hermaphroditically
•Takes Only One Individual to Start a Population
–Releases Close to 2,000 Juveniles per day; 50,000 Juveniles in One Year; and
More than 100,000 in a Lifetime
–Can Reproduce Within 3-6 months After Hatching
–Tolerant of Turbidity
–Can Stand Slight Salinity
No wonder they are invasive. A single self-fertilizing individual of these rather
dull, muddy shell fish can produce between 50,000 baby clams a year.
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Invasive, Non-Native Asian Clam (Corbicula fluminea)
•Coloring: Typically Light-Colored with Evenly-Spaced Concentric Rings
–Florida Version Is Yellow-Green to Light Yellowish-Brown on Its Periostracum
(outside of shell) and White to Light Blue or Purple Nacre (inside of shell)
–Habitat: freshwater, But Also Found in Brackish Water
–Shape: Shell Triangular, Relatively Thick, with Coarse Growth Rings
–On Shell Interior, Lateral Teeth Are Finely Serrated (visible with hand lens)
–Color: Periostracum Thick, Deciduous, Yellowish- to-Blackish-Brown
–Juveniles: Microscopic, Free-Floating Larvae, “D”-shaped, Less than 1/16”
•Similar Species: Native and Introduced Fingernail or Pea Clams (Sphaeriids)
Resemble Asian Clams
–Lateral Teeth Are Smooth vs. Serrated in Asian Clams Sphaeriids
–Generally Smaller, Have Thinner Shells and Less Prominent Growth Rings
•Habitat: Tolerates Low Temperatures Well (0-2°C); However, Temperatures of
16°C or Higher Needed for Reproduction
•Impact: Asian Clam Filter Suspended Matter from the Water Column
–Significantly Increases Water Clarity, Leading to Excessive Plant Growth and
Alters Lake Nutrient Regimes
–May Compete with Native Mollusks for Food and Habitat
–May Infest and Interfere with Irrigation Systems and Canals, and Block Water
Flow through Industrial Raw Water Intake Pipes
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Fingernail Clams (Family Sphaeriidae)
•Family of Small to Minute Freshwater Bivalve Molluscs
–Order Veneroida
–Also Includes Clams Formerly Placed in Pisidiidae
–Members of Subfamily Sphaeriinae Referred to as Fingernail Clams, While Even
Smaller Pisidiinae Are Pea or Pill Clams
•Superfamily: Corbiculacea, Family: Sphaeriidae
•Three Genera in Family: Musculium, Sphaerium, and Pisidium
•Species Distinguished on Basis of Shell Shape, Presence and Nature of
Striations and Details of Hinge Teeth Structure
–Beige, Smooth, Thin-Shelled Creatures
–Small, Shell Length Ranges between ¼” and 1”
–Cardinal Teeth (internal dorsal shell structures aid in shell valve articulation)
–Lateral Teeth (internal dorsal shell structures that aid in shell valve articulation)
•Habitat: Most Common in Sandy or Muddy Sediments of Lakes, Slow-Flowing
Streams, Seepages and Swampy Habitats
•Life span: Short-lived (1-3 years)
•Dispersal:
–Attach to Aquatic Plants as Tiny Juveniles
–Aquatic Plants Attach to the Feet of Waterfowl
–Waterfowl Drop Aquatic Plants in Adjacent Ponds
–In Addition, Freshwater Clams Are Ingested by Ducks, But Not Digested
•May Be Regurgitated Alive at Some Distance from Home
They can be easily missed as they tend to be buried
in fine sediment, and their small size and lack of movement
might make them look like small stones.
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Osprey Stormwater Retention Pond
Canna
Alligator Flag
Southern Blue Iris
Odorata Water Lilies
Canna
Pickerelweed
Spatterdock
Mexicana Water Lilies
Duck Potato
Osprey pond uses both Florida-native plants and non-native
Asian clams to remove nutrients from stormwater run-off.
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Calculation of Micro-Filtering Rate Within Osprey Pond
•Osprey Pond
–Stormwater Retention Pond in St Petersburg, FL (Pinellas County)
–Chemical-Free Maintenance for Five Years
–Oval: 100 ft X 155 ft (one-third acre)
–Capacity: 350,000 gallons (avg. depth of 3 ft)
•Freshwater Clams
–Measured Density: 300 / sq. ft (Agrees with Literature)
–Established Population Can Have >3,000/sq. metre (300/sq. ft)
–Can Rapidly Grow into Dense Populations (>2,000/sq. metre) [1,2]
–Maximum Densities Can Range from 10,000 to 20,000/sq. metre
–Area of Clam Coverage: 4,000 sq. ft (one-third of Osprey Pond)
–Number of Clams: (300 clams/sq. ft) (4,000 sq. ft) = 1,200,000 clams
•Asian Clam Filtration Rate: 100 ml/hr/clam (Range from 20 to 1370 ml/hr/clam) [3,4]
–Medium-Sized Clam in Ideal Conditions Filters Between 67.3 - 147.7 ml/hr [5]
•Variability Due to Food Density, Conditions, Mollusk Size and Pollution [6]
•Osprey Pond Calculation (350,000 gal., 0.0264 gal/hr/clam, 1,200,000 clams)
– (1,200,000 clams) (0.0264 gal/hr/clam) (350,000 gal/pond) = 11 hrs to Filter
Entire Pond
References:
1. McMahon, R. F. 1999, Invasive characteristics of the freshwater bivalve Corbicula fluminea. Pages 315-343 in R. Claudi and J. H. Leach, editors. Nonindigenous freshwater organisms: Vectors, biology, and impacts. CRC Press, Boca Raton, FL
2. Gottfried, Peter K. 1979, The Population Dynamics and Distribution of Corbicila Manilensis (Philippi) in a Spring-fed Central Florida Stream, University of Central
Florida College of Natural Sciences, M.S. Thesis
3. Lauritsen, D.D. 1986, “Filter Feeding in Corbicula fluminea and its Effect on Seston Removal,” Journal of the North American Benthological Society, 5(3):
pp.165-172
4. Lauritsen, 1986), Lauritsen, D.D. 1986. Filter Feeding in Corbicula fluminea and its Effect on Seston Removal. Journal of the North American Benthological
Society. 5(3):165-172 and Lauritsen, D.D. and Mozley, S.C. (1989). Nutrient excretion by the Asiatic clam Corbicula fluminea. Journal of the North American
Benthological Society, 8(2): 134-139.
5. Lauritsen 1986, Phelps, H.L. 1997. Life History Data for the Asiatic Clam (Corbicula fluminea). Report to the Delaware River Corbicula Bivalve Project for the
Delaware River Basin Commission (DRBC-F98D-1/2). 11p.
6. Widdows J. 2001. Bivalve clearance rates: Inaccurate measurements or inaccurate review and misrepresentation? Mar. Ecol. Prog. Ser. 221:303-305.
A simple calculation shows that the entire pond (0.3 acres) can pass
through the micro-filtering within a day or so.
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