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The ‘perfect storm’ and 2011 superbloom
From early spring through late fall 2011, two massive blooms of phytoplankton caused a loss of seagrass throughout much of the Indian River Lagoon system, with the problems extending from the Titusville area of the lagoon to just north of Fort Pierce Inlet. This bloom and seagrass decline far exceeded any documented or remembered events in terms of size of the area affected, intensity and duration of blooms, and rate and magnitude of seagrass loss.
The smaller bloom in the central lagoon — from Eau Gallie south to Vero Beach/Fort Pierce — covered approximately 47,000 acres. This bloom was moderately intense.
The other bloom reached immense proportions and earned its own label, “superbloom.” The 2011 superbloom covered approximately 130,000 acres of open water, north of Eau Gallie to the Scottsmoor area.
There is no one, simple answer as to why the superbloom occurred, but it appears to have been a “perfect storm” of events. The scope of the superbloom and seagrass die-off was surprising because it followed a two-year drought. Dry times are generally good for the lagoon because it means less storm water — and fewer nutrients — entering the estuary. Most nutrients in the lagoon (75 to 80 percent) originate from rainfall runoff and stream drainage. In addition to a reduction in pollutant-laden storm water, fewer contaminants “rained” down on the waterway from the air during the drought.
Some scientists believe an internal shift or flux in nutrients might be the primary mechanism that fueled the bloom. This shift was potentially related to extreme weather conditions that may have created a “perfect storm” resulting in a superbloom. Many factors may have been at play — such as record cold temperatures and the unusual disappearance of drift algae — and many questions and possibilities are being explored.
Drift macroalgae, a mix of abundant aquatic macrophytes, crashed in mid-2010 and has yet to recover. Without drift algae acting as a nutrient “sponge,” nutrients may have become available to feed the superbloom.
The winter of 2009–2010 marked the coldest winter and the coldest December in the region since records began being kept in 1937. Extremely low water temperatures followed, dropping to 39 degrees Fahrenheit in January 2010, and remaining at 44 degrees Fahrenheit for days in December 2010. These record low water temperatures may have impacted one or more biotic communities, leading to a reduction in grazing pressure on phytoplankton (algae), or to an increase in nutrient availability for phytoplankton growth. An additional stress imposed by the second cold snap (December 2010) in combination with the drought-induced hypersalinity of early 2011 may have dampened the recovery of drift algae, grazers or other biota impacted the previous year. These and other topics are being investigated by the Indian River Lagoon Consortium and will be addressed as part of the Indian River Lagoon Protection Initiative.
During the first three months of the bloom (April through June 2011), water transparency declined. Algae blocked the sunlight that drives photosynthesis, which seagrasses need to support their growth and survival. Seagrass is the lifeblood of the lagoon, serving as a nursery for juvenile fish, habitat for shrimp and a food staple for manatees.
Seagrass losses were substantial. Compared to seagrass coverage in 2010, grassbeds were reduced by 60 percent, or about 47,000 acres overall.
This extensive loss of grassbeds could be a staggering blow to the regional economy that is dependent upon the estuary, particularly its fisheries. The harvest of seatrout and other seagrass-dependent fish is strongly influenced by seagrass coverage. Also, seagrass may contribute $5,000 to $10,000 per acre per year to the local economy, meaning that the 2011 seagrass loss represents a potential reduction of $235 million to $470 million for each year it remains absent.
Alarming trends in the lagoon continued in early 2013 with the deaths of manatees and pelicans. The St. Johns River Water Management District, state and federal agencies, universities, research centers and outside experts are collaborating to determine whether the manatee and pelican deaths are directly connected to the superbloom and subsequent seagrass die-off.
Ed Garland at (321) 676−6612 or firstname.lastname@example.org.
Updated on 5-16-2013