Environmental Benefits of the Florida Hard Clam Culture Industry
Leslie Sturmer1, Shirley Baker2, Kelly Grogan3, and Sherry Larkin3
1 University
of Florida IFAS Cooperative Extension Service and Florida Sea Grant; 2 UF IFAS School of Forest Resources
and Conservation, Fisheries and Aquatic Sciences Program; and 3UF IFAS Food and Resource Economics Department
Shellfish (oysters, clams, mussels) provide environmental benefits
to the coastal waters in which they are grown. In turn, shellfish
farming can provide local communities with a variety of ecosystem
services, whose value can be quantified. To demonstrate the sustainability of hard clam aquaculture in Florida, three ecosystem services
(water filtration, nitrogen removal, and carbon storage) were
examined. Efforts focused on assembling values specific to hard clam
Mercenaria mercenaria culture, identifying information gaps, and
translating information to the industry. The value of the contribution
of the hard clam industry to nitrogen removal and carbon sequestration was assessed by calculating costs that would be incurred to
replace the industry’s ecosystem services with the next best
alternative. Results demonstrate the important contribution of hard
clam culture to coastal ecosystem services.
Determine Values of Harvest-sized Clams
Measurements, particularly for
harvest-sized clams at water temperatures found in Florida, are not
available through the literature. To
address these information gaps,
laboratory measurements were
obtained. The filtering rate of clams
was measured in the lab using a
fiber-optic colorimeter, which
measures the turbidity of a phytoplankton solution. As clams removed
phytoplankton from the water, the turbidity declined over time. Using this data,
the volume of seawater cleared of phytoplankton per day for three commercial
grades of hard clams was calculated. The amounts of nitrogen and carbon
removed from the ecosystem upon harvest were determined by measuring the
contents of both tissues and shells. Clam tissues and shells were dried, weighed,
and ground to fine powders. Stable isotope mass spectrometry was used to
determine the proportion of nitrogen and carbon in the sample. From these
data, total weight of nitrogen and carbon of each clam was calculated.
Clams Store Carbon from the Atmosphere
A single littleneck-sized clam can store 2.76 grams of carbon.
Florida hard clam aquaculture provides
economic values for ecosystem services
generated by the industry; values that can
help decision makers determine whether
to promote or expand the industry.
Value of Services Provided by Clam Culture
SEAWATER FILTRATION
544 million gallons of seawater were
filtered by the statewide production
of 136 million clams*.
N
NITROGEN REMOVAL
25.4 thousand pounds of nitrogen
were removed from the
coastal waters.
Clams Clean the Water by Filter Feeding
A single littleneck-sized clam can filter 4.5 gallons of water per day.
As clams feed, they create
currents that move water through
the animal via their siphons. By this
very act of feeding, clams filter
phytoplankton, microorganisms,
and detritus. In doing so, they
improve water clarity by reducing
sediment loads and turbidity and
removing excess nutrients from the
water. Clearer water allows more
sunlight to penetrate, which aids in
the growth of important seagrasses and increases oxygen in the water.
Clams Remove Nitrogen from the Water
A single littleneck-sized clam can remove 0.09 grams of nitrogen.
Clams play an important role in the cycling of nitrogen. Clams do not absorb
nitrogen directly from their environment, rather they feed on naturally-occurring
phytoplankton, which use dissolved inorganic nitrogen, available in the water, to
grow. Thus, clams incorporate nitrogen from their food into their tissues and
shells. When clams are
harvested, the accumulated
nitrogen is removed from the
water. In turn, clams release
nitrogenous waste (urine)
that can be used by phytoplankton. Some of the
filtered nitrogen is deposited
to the sediment as feces and
pseudofeces. These are
decomposed by bacteria,
transforming nitrogen into
other forms.
Clams convert carbon
into calcium carbonate
shell, which is primarily
derived from atmospheric
carbon dioxide dissolved in
seawater. Thus, the shells
of clams provide a longterm carbon sink. Clams
also process carbon while
they are growing. Just like
other animals, they produce carbon dioxide as a
waste product of respiration.
In addition, the carbon (particulate organic carbon) deposited in the sediments
as feces and pseudofeces is consumed by a variety of organisms, such as worms,
brittle stars, and other deposit feeders.
C
CARBON STORAGE
760.6 thousand pounds of carbon
were sequestered from the
coastal environment.
The contribution of the Florida clam
industry to nitrogen and carbon extraction
was assessed. The costs that would be
incurred to replace the industry’s services
with the next best alternative were
calculated. For nitrogen removal,
replacement cost values were
based on the costs of wastewater
treatment plants in Florida cities. Values
per pound of nitrogen removed, ranging
from $3.44 for Clearwater to $5.22 for Fort
Myers, were based on land values and cost
of living, factors that affect the cost of
treatment plants.
For carbon sequestration, the creation and
maintenance of pine tree plantations was used as
a possible alternative to clam production. Costs
included pine production, as well as the value of
the land in an alternative use. In counties with
high agricultural, commercial, or urban land
values, this opportunity cost of utilizing the land
as a pine plantation was high. The highest values
($119 per ton) were estimated for Collier County
in southwest Florida, while the lowest ($0.71 per
ton) costs were in Franklin County, a rural area.
Farm Environmental Benefits Calculator
Several deliverables, such
as the Clam Farm Benefits
Calculator, allow growers to
inform buyers, consumers, and
resource managers that shellfish
aquaculture is a sustainable
“green” industry.
ECONOMIC VALUE
Value of these benefits was estimated
at $99,680, which represents the
public good value provided to
Florida citizens at no cost.
*Based on production results from the 2012 Florida Aquaculture Survey
conducted by the U.S. Department of Agriculture.
What is an Infographics Poster?
The highlights of this study on environmentally-beneficial ecosystem
services and their value provided by the 2012 Florida hard clam production
are displayed as informational graphics in the middle panel of this poster.
Infographics are visual representations of information, data or knowledge
intended to present information quickly and clearly. Infographics have evolved
in recent years for mass communication, and thus are designed with fewer
assumptions about the readers knowledge base than other types of visualizations. This poster was designed by the UF IFAS Department of Agricultural
Education and Communication.
With inputs of farm location
and number of clams harvested
per year by grade size, the
Calculator provides an estimate
of the economic value of the
benefits that a grower’s crop
provides on an annual basis.
The Calculator and schematics displayed in this poster can be accessed
at the website, http://shellfish.ifas.ufl.edu.
Funding for this project was obtained from the Florida Department of Agriculture
and Consumer Services through the 2014-15 Florida Aquaculture Program.