many coastal waterbodies, excess nutrients cause an increase in algae and
phytoplankton that blocks sunlight to the lower depths. The decrease in
sunlight eventually kills bottom-dwelling plant life, leading to lower
dissolved-oxygen concentrations in the water and decimating prosperous habitats
for other species.
Traditional methods to
reduce nutrients include upgrading water resource recovery facilities (WRRFs)
and reducing stormwater runoff, which carries fertilizer and wastes from the
land into estuaries and coastal waters.
But bivalve shellfish
also offer the ability to filter the water column and remove nitrogen.
Incredibly, a single adult oyster can filter up to 190 L/d (50 gal/d). The
clearer water allows sunlight to penetrate so that foundations of the food
chain can thrive; once water clarity increases, bottom vegetations, such as
In Southern California,
native Olympia oysters were once ecologically and economically
dominant along the coast. These bivalve shellfish were ecosystem engineers
for the bays and estuaries, as well as enablers of prosperous habitats for
other species. They also were considered commercially important as a delectable
food source until a combination of overharvesting, dredging, pollution, and
wetlands destruction in the 1930s depleted natural populations.
Now, KZO Education (Long
Beach, Calif.), a research and education nonprofit organization, is
collaborating with scientists from the University of Southern California (Los
Angeles) Wrigley Institute for Environmental Studies (Catalina Island, Calif.)
and the U.S. National Oceanic and Atmospheric Administration’s Milford (Conn.)
Laboratory to quantify and document the environmental effects of farming
oysters and mussels offshore in California as part of its Offshore Mariculture
Monitoring Program. This team of scientists also might explore the potential of
bivalve shellfish for the bioextraction of nutrients from Long Beach Harbor.
Nutrient pollution in San Pedro Bay
The combined Los Angeles and Long Beach
harbors consist of about 730 ha (1800 ac) of water in the inner navigation
channels and 2430 ha (6000 ac) of water in sheltered anchorages and navigation
channels. As with many coastal waters, these harbors have been degraded by
nutrient pollution, and the Los Angeles River is a major culprit. The river
runs 82 km (51 mi) from the Santa Monica Mountains across 18 municipalities
that are home to 1 million residences before dumping 5180 m3/s
(183,000 ft3/s) of nutrient-loaded water into San Pedro Bay.
According to a study
conducted in 2000 by the City of Los Angeles, the Los Angeles Regional Water
Quality Control Board, and the Southern California Coastal Water Research
Project, the Los Angeles River contains three primary sources of pollution:
discharge from three WRRFs, outflow from river tributaries into the river, and
According to the report Characterization
of Water Quality in the Los Angeles River, the study was conducted in what
would be considered a fairly dry month and showed that, “[t]he three water
reclamation plants discharged the majority (72%) of the volume flowing in the
Los Angeles River during this study.” This discharge was found to contain “the
highest concentrations and greatest mass emissions of nutrients including
nitrate, nitrite, ammonia, and total phosphate,” the report says.
The Los Angeles River
Estuary connects the Los Angeles River to San Pedro Bay. It has 4.2 km (2.6 mi)
of soft bottom, with an average width of 122 m (400 ft). The estuary is about
1.8 m (6 ft) deep, depending on the season and tidal influences, and produces
about 302,800 m3/d (80 mgd) during drier months. Point and nonpoint
source urban runoff and the three WRRFs provide year-round river flow.
Bivalve shellfish bioextraction services
Employing a 6-m × 7.6-m
(20-ft × 25-ft) mussel raft in New York City’s Bronx River as their field
location, researchers from the U.S. National Oceanic and Atmospheric
Administration’s Northeast Fisheries Science Center’s Milford Laboratory
completed a 2-year pilot study to test how effectively ribbed mussels can
remove nitrogen and other excess nutrients from water. Scientists monitored the
condition of the mussels, which were grown on lines hanging below the raft, as
well as local water quality, to understand how each responded. They also
monitored mussel-feeding activities within a filtration apparatus. Local water
was pumped directly across each mussel before exiting the chamber.
The mussel-raft study
was part of longer-term efforts to improve water quality in Long Island Sound.
The pilot project evaluated the potential for shellfish aquaculture to increase
biological filtration activity in an urban environment. Results from the pilot study
also contributed to a system-scale evaluation of bioextraction for all of Long
Island Sound and helped characterize the ecosystem services that would be
provided by this approach, such as improvements in water quality, removal of
bacteria, and assimilation of nutrients. Nearly $1.5 million in research and
development funds have been expended to document that the bivalves on the raft
filtered more than 18,925 m3/d (5 mgd).
The Milford Laboratory
researchers are planning to transfer and apply lessons learned, as well as
their technologies and methodologies, to Long Beach this summer to quantify
bivalve bioextraction potential at the first offshore shellfish farm in U.S.
federal waters about 16 km (10 mi) from the outflow of the Los Angeles River.
The Los Angeles River
Estuary would be an ideal location for restoring native Olympia oyster beds,
which are typically found in the subtidal zone and are bordered by mud flats at
high elevations and by eelgrass at low elevations. Olympia oysters are found at
depths of zero to 61 m (zero to 200 ft) and attach to rocks and gravel. They
survive in a broad range of habitats but are most abundant in estuaries and
small rivers. While tolerating brief exposure to low salinities, they thrive at
salinities greater than 25 ppm.
Hard-bottom or substrate
habitats are ecologically important, as they provide food, shelter, and
spawning and nursery areas to various fish, shellfish, and other organisms.
Hard-substrate habitats in San Pedro Bay include the breakwaters and jetties
within the harbor complex, as well as pilings that support wharves and piers,
and along the shoreline of the basins and channels.
Restoring native Olympia
oysters is a promising proposition for the Long Beach Harbor ecosystem,
resulting in cleaner water for San Pedro Bay. The City of Long Beach is
presented with a timely opportunity for demonstrating and validating the
efficacy of innovative bivalve bioextraction technologies for coastal