Deformed Forams in Biscayne Bay
Why were forams in Biscayne Bay studied? This study is just one small part of a much bigger effort to restore the Florida Everglades ecosystem. As you can see in the map below, a large portion of the state of Florida was once covered by the Everglades (shown in light blue); but urban development and drainage have severely damaged this ecosystem. Today the Everglades is only half this size. Because the Everglades ecosystem is so important to the people and wildlife of Florida, the Comprehensive Everglades Restoration Plan (CERP) became law in 2000 and it commits nearly $8 billion to restore and protect these water resources.
Biscayne Bay is located off the southern part of Florida, south of the city of Miami and north of the Florida Keys. Inset map shows Florida relative to Cuba, the Atlantic Ocean and the Gulf of Mexico. (Credit: USGS Open File Report 02-308, US Department of the Interior)
Benthic forams were studied to help establish present environmental conditions in Biscayne Bay. The Everglades and Biscayne Bay are ecologically connected; so scientists need to understand what the current condition of Biscayne Bay is, so they can monitor its health as Florida Everglades restoration takes place.
What was their study plan? In contrast to the previous studies involving the petroleum industry and the Integrated Ocean Drilling Program, pollution studies make use of modern forams. Scientists collected thirty-eight (38) bay floor grab samples along the western edge of Biscayne Bay in a pilot study conducted in 2000 and 2001. See map below for sampling sites marked by yellow triangles. Triangles are located adjacent to Dinner Key Marina, Snapper Creek, and Black Point Landfill, and also in a long line across the bay away from the landfill. (Ignore the red squares for now; we will talk about them shortly). Scientists wanted to determine whether benthic foram populations were showing any signs of stress, and if so, where the stressed forams were living.
This is a close-up view of Biscayne Bay (shown in blue) with the coast of Florida (grays and browns) to the left. Notice the clusters of yellow triangles near Dinner Key Marina, Snapper Creek and Black Point Landfill. These are the locations of bay bottom grab samples taken during the Phase I pilot study. Phase II samples are shown in red. (Credit: USGS Open File Report 02-308, US Department of the Interior)
What did scientists expect to see? Areas near Dinner Key Marina and Black Point Landfill were thought to be polluted. Marinas often are the site of heavy metal pollution from metallic paints used on the bottoms of boats and from metallic anodes that offer corrosion protection to metal surfaces in salty water. In addition, landfills may have heavy metals and other pollutants seeping from their fill. Scientists thought they might see evidence of heavy metal contamination at these two sites, and little or no evidence of contamination at Snapper Creek and sites in the middle of Biscayne Bay.
What foram evidence might indicate heavy metal pollution? One factor to look for is the presence of "opportunistic" taxa. Scientists have learned in previous studies, which groups of species are more likely to be present when water quality begins to degrade. These groups are called "opportunistic", meaning that they move into an area when other species can't tolerate the conditions and move out. The presence of opportunistic taxa is a clear sign that something is creating stress, but it does not necessarily prove that the problem is heavy metal contamination. Stress may be due to variable salinity, low oxygen, the presence of pollutants or a combination of all three. See some examples below of opportunistic taxa.
In addition, forams exposed to heavy metal pollution often show test deformities. However, test deformities may also occur as a result of physical stress, such as living in an area with active water movement which can crack or break tests. In these cases, the repaired test may also look deformed. So test deformities are not automatic indicators of heavy metal pollution. Consequently, scientists also run chemical tests to verify the presence of heavy metals before drawing their conclusions.
What did they find? First, scientists identified opportunistic taxa at every yellow triangle site, indicating that benthic foram populations were under stress everywhere they had sampled. The percentage of opportunistic forams was highest at sites where chemical analyses also indicated the presence of heavy metal contamination. In addition, they discovered that the percentage of opportunistic taxa decreased in the middle of the bay. These results suggest that heavy metal contamination may be a stress factor, but they do not eliminate other factors such as salinity and low oxygen from also playing a role. The good news is that the forams in the center of the bay indicate that water quality there is better than near the densely urbanized shoreline areas.
Second, over 70% of the sample sites contained benthic foram specimens with deformed tests. Deformities ranged from minor to severe, with the most severely deformed tests located adjacent to the Black Point Landfill. The images shown below illustrate the kinds of deformities encountered. In these sets of images, normal specimens are shown on the left and deformed specimens of the same group are shown on the right.
Miliolinella normal on the left and deformed on the right.
Triloculina linneiana normal on the left and deformed on the right.
One surprising result was that the most severely deformed specimens were found adjacent to the Black Point Landfill to the south. This was surprising because chemical analyses of the sediments indicated that the highest levels of heavy metals were found in northern sediments. One explanation for this seemingly anomalous result is that the sediment type changes from north to south. Sediments are fine grained and clay-rich to the north and more sandy and clay-poor to the south. Perhaps heavy metals are leaching from the Black Point Landfill, but the sandy soil does not preserve a record of it. Or perhaps some factor other than heavy metal pollution is causing the test deformities.
A second, more regionally extensive study of Biscayne Bay is being conducted and sample locations for this second study (Phase II) are shown in red squares on the map above. Results from this study should be known soon.
Want to see another example?
Foraminifers as Bioindicators - Beautiful SEM images of forams, plus information on how forams are sampled and analyzed in pollution monitoring.
USGS Open File Report 02-308 (2002) Chemical Pollutants and Toxic effects on benthic organisms, Biscayne Bay: A pilot study preceding Florida Everglades restoration. Retrieved Nov. 1, 2004 from http://pubs.usgs.gov/of/2002/of02-308/ofr-02-308.pdf
Revised on: January 3, 2005