March 31, 2014
Brown algae is closing in on N.C.
waters from the south and the north
By PAT GARBER
kills, decreases in shellfish, murky brown water, and loss of
underwater grasses -- these are things no one wants to see in their
coastal community waters. But these are the effects of a brown algae
that is becoming more and more common in the estuaries of the eastern
United States. Brown algae blooms, also known as tides, have, in the
last 30 years, become a huge problem in such states as New York,
Virginia, Florida, and Texas.
The Labrador Current, a huge
river of frigid water winding down through the ocean from the north,
converges with the Gulf Stream, flowing with warm water from the south,
just offshore of Hatteras and Ocracoke islands. Both streams pass
through waters where brown algae flourishes--Aureococcus
anophagefferens to the north and Aureoumbra lagunensis to the
Is it just a matter of time before North Carolina’s estuaries are infected?
March 26, Dr. Nathan Hall gave a talk and slide show at the Ocracoke
Community Center to explain what brown algae is and the dangers of
having it show up in Pamlico Sound and other North Carolina waters. The
program was the last of four scheduled by the National Park Service to
share knowledge with the public.
Hall works out of the
University of North Carolina at Chapel Hill Institute of Marine
Sciences at its Coastal Environmental and Microbiological Processes
Laboratory, trying to learn more about brown algae and how to prevent
it from invading the state’s waters.
The first recorded brown
algae bloom occurred in 1985 in the bays of New York state. Five years
later, there was a bloom in Texas of a separate but similar species of
brown algae. Since then they have had repeated blooms and the two
species have spread south, east, and north, traveling most likely in
the currents of the Labrador and Gulf Streams.
Dr. Hall, are a kind of phytoplankton -- tiny unicellular plants that
drift in the water. Like other plants, they require light and mineral
nutrients, and they conduct the process known as photosynthesis by
which they convert carbon dioxide into oxygen. Phytoplankton,including
most algae, are an important part of the food web. There are several
hundred species in Pamlico Sound, the estuary that lies west of
Ocracoke and Hatteras Islands, and they produce 80 percent of the food
there. Tiny floating animals, known as zooplankton, feed upon them, and
they are eaten by fish, shellfish, and other species that live
Brown algae are much smaller than most
phytoplankton and they can often out-compete and replace them. They do
not contribute to a healthy food chain. In fact, their presence can
lead to massive die-offs. What marine biologists call grazers --
zooplankton, clams, oysters, and other shellfish -- stop growing and
eventually die when they eat brown algae, or in the presence of it,
cease to eat at all and starve. In New York's Peconic Bay, commercial
scallop harvests dropped to near zero when brown algae blooms showed up
in the late 1980s, and they have not yet recovered. Hard clams, or
quahogs, likewise disappeared in Great South Bay, New York, when brown
tides began in the mid-1980s.
Clams, like oysters and other
shellfish, are important natural water filterers that help keep estuary
waters clean. Studies show that the time it took to filter Great South
Bay dropped from three days in 1976 to three months in 2005, due to
clam losses caused by brown algae blooms. Laboratory tests of oyster
larvae showed that few of those feeding on brown algae survived, and
even fewer developed into adult oysters.
Brown algae blooms
drastically reduce light penetration, causing seagrass, an important
marine habitat which requires a certain amount of light, to die off. As
seagrass beds disappear so do the many forms of life that depend on
them. Studies at the Indian River Lagoon in Florida indicate that
seagrass beds covering nearly 75,000 acres in 2009 dropped to fewer
than 30,000 acres in just two years, after the onset of a brown algae
Large amounts of algae lead to oxygen depletion in
coastal waters, which in turn leads to fish die-offs. Algae do not
conduct photosynthesis at night but instead use up oxygen. When they
die, their decomposition also reduces oxygen, especially near the
bottom of estuaries. Reported fish kills in Florida's water jumped
nearly 400 percent during a brown tide in 2012.
with brown algae turns brown and murky, and while brown algae poses no
known health threat to humans, it does not entice one to swim or kayak
What causes brown tide blooms and how do they out-compete other phytoplankton? Hall was quite clear in his answer.
"We don't know, but we do know that we don't want them," which is why he and other scientists are busy trying to find answers.
study the algae through such methods as pigment analysis, which tells
how much and what kinds of phytoplankton are present; through
microstudy and DNA analysis, which identifies species; and with
satellite imagery, which shows how much is present over large areas.
They go out in small boats to collect water samples, attach monitoring
equipment to ferries, including the Hatteras Ferry, and use profiling
buoys to check water at different depths.
They have learned
that their small size gives brown algae an advantage, especially when
light or nutrients are in low supply, because they have a larger
surface area relative to their mass, which allows them greater
absorption. They know that in a healthy pre-tide ecosystem there is a
balanced mix of light, varied algae, nutrients, and grazers, whereas in
a brown tide the brown algae dominates and reduces the other factors.
They know that when brown algae form a small percentage of the total
algae, grazers eat them as readily as other algae with no bad results,
but when a brown tide is dominant, they stop eating or die.
algae seem to have a higher tolerance for salinity than most other
species, so that if drought raises the salinity of a body of water,
they are more likely to survive. Like other algae, the brown species
thrive in nutrient-rich water, particularly in the nitrogen and
phosphorus found in fertilizers and animal waste. Agricultural and
run-off and sewage are two of the main causes of algae blooms and
subsequent fish kills.
Scientists know that once a brown tide is
in effect, it is self-propagating, eliminating other kinds of algae.
They do not know for sure, however, what causes brown tide blooms to
"It's the old chicken and egg problem,” Hall said. “Which comes first?"
Carolina's Albemarle and Core sounds may have too much fresh water to
encourage a major brown tide. But the Pamlico, which is the second
largest estuary in the country and the most important nursery for
Southeast fisheries, has salinity levels, temperatures, depths, and
nutrient loads similar to estuaries that have had brown tides.
neither species of brown algae has shown up here is a mystery. It may
be because its tributaries are able to effectively filter out nutrients
or because it has strong, healthy grazers.
The main preventives
which could discourage brown tides are nutrient management, which means
keeping nitrogen and phosphates from entering the tributaries, and
prudent management of seagrass and shellfish resources. In other words,
promoting a healthy, balanced ecosystem in Pamlico Sound is the best
way to prevent brown tide blooms.
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