[USA] Brown tide appears to be growing worse in Brevard County.
The Indian River and Banana River lagoons recently tested at some of the highest concentrations of brown tide algae ever recorded, levels potentially lethal to juvenile shellfish and other marine life.
The brown tide algae — Aureoumbra lagunensis — makes up almost all of the phytoplankton in the water, recent tests show. That puts at risk some 180,000 live oysters that thousands of volunteers have helped to grow and place onto three pilot reefs in the lagoon, as well as countless other lagoon life. And if the lagoon remains in bloom into the spring, the tiny algae could cloud sunlight from reaching seagrass, sunlight that the seagrass needs to photosynthesize during the vital bottom plant’s peak growing season.
“At these kinds of levels, seagrasses are not receiving very much light,” said Charles Jacoby, a supervising environmental scientist with the St. Johns River Water Management District.
Seagrass is the linchpin of the lagoon food web. It’s the manatee’s main diet. Mutton snapper, lane snapper, gag and red grouper, spotted sea trout, blue crabs and other marine life depend on the grass for habitat. Studies have shown one acre of seagrass can support as many as 10,000 fish.
Recent water tests by the district showed:
- Banana River Lagoon reached 2.8 million cells per milliliter of brown tide in early January, with brown tide algae making up 88 percent of the total volume of phytoplankton in the water.
- Northern Indian River Lagoon reached 1.2 to 2.2 million cells per milliliter of brown tide, 88 percent to 93 percent of the total volume of phytoplankton.
- This week, concentrations of chlorophyll — an indicator of algae blooms — topped levels seen in the 2011 “superbloom,” the worst known bloom in the lagoon’s history that killed more than 30,000 acres of seagrass.
- Brown tide may be dissipating in parts of the Mosquito Lagoon, but simultaneously has spread south into Melbourne.
“Even if this does affect our oysters, this is good information for us and for the lagoon,” said Sammy Anderson, who manages Brevard Zoo’s oyster restoration program. Part of the project is to monitor how the oysters do in various conditions to learn how and where best to grow them.
This year’s brown tide arrived much earlier in the year and now is prominent in much of the Banana River and Indian River lagoons, from Cocoa south to Melbourne.
The same brown tide species hit Laguna Madre and Baffin Bay along the Gulf Coast of Texas in the early 1990s, killing off seagrass for years. The bloom lasted almost eight years, making it the longest continuous harmful algae bloom ever recorded.
A similar brown tide species emerged in coastal waters off New England and New York in the mid-1980s, devastating scallops, clams and seagrass in Long Island’s southern bays.
The same algae species also has bloomed in Guantanamo Bay, Cuba, in recent years.
Biologists aren’t sure how brown tide got here, whether the species always resided in the lagoon or was introduced from the ballast water of a boat. Brown tide blooms in the Long Island area have been linked to nutrients from septic tanks polluting the groundwater, then oozing up in the bays.
A study last year by researchers at Stony Brook University in New York found absence of grazing pressure enables brown tide to out-grow other phytoplankton. Under very salty conditions, brown tide is able to resist zooplankton, the tiny marine organisms that typically graze on plankton.
Brown tide algae first began appearing in lagoon water samples in 2005, but in low levels. Then in the summer of 2012, it bloomed in Mosquito Lagoon, then moved west to the northern Indian River Lagoon. It was the first major bloom of the species documented in Florida. As much as 50 square miles of lagoon seagrass had already died a year earlier, after another type of algae — the so-called “superbloom” — spread from Titusville to Eau Gallie. A separate, concurrent bloom stretched from Eau Gallie to south of Vero Beach.
In all, more than 47,000 acres — 73 square miles — of seagrass would die in the blooms.
If water temperatures dip, the brown tide may die off. But if the water stays warm and the bloom lasts into spring, the algae could blunt seagrass recovery.
“We’re kind of live in hope that this will tone down and fade away,” Jacoby said.
What is brown tide?
Scientific name of species in the lagoon — Aureoumbra lagunensis
The individual algae cell is only 4 to 7 microns in diameter. So it would take more than 200 brown tide cells, side by side, to stretch across the period at the end of this sentence.
Why is it called brown tide? When levels reach 1 million to 2 million cells per milliliter of water, the water appears brown.
Source: Texas Parks and Wildlife
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