SALT MARSHES

The Indian River Lagoon, a shallow lagoonal estuary, lies within Indian River County and is one of the most biologically diverse estuaries in North America. A blend of salty ocean water and freshwater from rivers and creeks, the lagoon spans 156 miles of Florida’s east coast – from its northern point at Ponce de Leon Inlet in Volusia County to its southern boundary in Martin County. This brackish water is influenced more by winds than by tide. 

Over 50,000 acres of salt marshes line the length of the lagoon. These marshes comprise two distinct zones, “low” marshes and “high” marshes border both sides of the lagoon as well as on islands within it. The twice-daily flooded low marshes do not produce mosquitoes but the irregularly flooded high marshes are capable of producing saltmarsh mosquitoes in high numbers when flooded by high tides or most commonly rainfall.

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The “low” marsh is land that is flooded by the daily tides. In Indian River County it is dominated by red mangrove and coastal grasses such as Smooth Cordgrass. Low marsh is rarely a source of mosquito problems because the tides constantly flush through it.

 The “high” marsh is flooded by seasonal tides, storm-driven tides or rainfall only. Vegetation consists of black and white mangrove and various understory succulents and grasses. It is in this irregularly-flooded high marsh that the saltmarsh mosquitoes, Aedes sollicitans and Ae. taeniorhynchus, lay their eggs in vast numbers.

Unlike other mosquitoes, the saltmarsh mosquito will not lay its eggs directly onto water. Instead, it waits for water levels to fall slightly and lays its eggs (oviposits) in the damp soil or mud. This peculiarity makes keeping the marsh covered with water the best and most economical form of mosquito control in salt marsh areas.

The eggs hatch almost immediately upon flooding, by rainfall or tides, and the mosquito rapidly progresses through four larval stages called “instars”. In later stages, the larvae commonly congregate and forms “balls” that can measure three feet wide and contain 100,000 individual mosquito larvae. Such balls may be found dotted all over every shallow pond and puddle in the marsh, so even a small area of marsh may produce billions of mosquitoes from a single rainfall or tide event.

A 1-2 day pupal stage allows the larval form to go through metamorphosis into the adult flying/biting form. Pupae are mostly immune to our larvicidal chemicals and it's too late to get them in the water once they reach this stage. The adults emerge in a synchronized flight, mate in the air and then disperse over many miles seeking a blood meal to provide protein so they can start the cycle all over again.