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Osprey as a Sentinel Species in the Detection of Polluted Water

Updated: Sep 9, 2022

The Ospreys that used to nest on the navigation marker in Smokehouse Bay have left. These majestic birds depended on fish in the bay as a food source. Eagles used to perch in a large Norfolk Pine on our property and observe the bay. The fish have left the bay, and the osprey and eagle no longer have a food source. Why did the fish leave? No oxygen. Why did the seagrass die? No light. Why did the manatee leave? No seagrass as food. It is not that the ospreys have left all of Marco Island, but just the areas where they cannot find food, like Smokehouse Bay.

The Dissolved Oxygen (DO) in the canals on Marco Island is experiencing a 5-year-long steady decline and is experiencing “hypoxic hot spots,” i.e., near total absence of oxygen in the water. The waterways are choked with algae fed by the nutrients in the reuse water (purple pipes) from the Wastewater Treatment Plant (WWTP). The algae block the sunlight from reaching the bottom of the bay, and the seagrass has died.

The City of Marco Island uses our bays and canals as the final process step in sewage treatment. Very effective for the city. Low cost. The disadvantage to the residents is that the waterways are no longer full of aquatic life and are just part of a sewage treatment process. The canals are discolored and smelly.

Research currently explores the relationship between algal blooms and degenerative brain diseases such as Parkinson’s, Alzheimer’s, and ALS. Algal blooms and benthic mat releases regularly occur on Marco, typically in the warmer summer months. The “benthic mat” is an accumulation on the canal bottom caused by the nutrients from the partial sewage spread across Marco in the form of reuse water (purple pipes) from the sewage treatment plant.

We put a mini reef under our dock on Smokehouse Bay 2 years ago. There was abundant fish life then. We had also installed underwater lights along the pier. It was like our own huge private aquarium. Hundreds of minnows darting in and out of the cover of the dock had attracted numerous larger species of fish. Small crabs skittled sideways through the water periodically. This aquatic activity attracted many birds that would perch on the seawall and observe the activities with great interest. All gone. I’m sure many residents living on a canal or bay have a similar story. Smelly-colored water is all that is left.

As described by Stanley Manahan in “Environmental Chemistry:” “An organism that has been described as a worldwide sentinel species to assess and monitor environmental pollution in rivers, lakes, reservoirs, and estuaries is the osprey, a large raptor bird with a wingspan that can exceed 1.5 meters. Found in all continents except for Antarctica, the osprey feeds almost exclusively on fish.” When the fish are gone, the osprey leaves the area.

Dissolved Oxygen (DO) levels in the Delaware Estuary along the US east coast have increased significantly over the last 30 years because of improved wastewater treatment. Osprey is becoming a more familiar sight there. This shows that it can be done. The loss of the osprey is just one more tradeoff the Marco residents are forced to endure so that the condos and golf courses can benefit from “cheap fertilizer” in the polluted reuse water.

Nanette Rivera

Candidate for City Council

Marco Island, Florida

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