Seaweed-Seagrass Information and Control

 

Seaweed and Seagrass Information

 

The Village receives many reports from residents in the summer about the increased accumulation of seaweed and seagrass along the Key Biscayne beach. Floating Sargassum seaweed (a brown macroalgae) is transported from the Gulf of Mexico via the Loop Current to the Atlantic Ocean and Caribbean Sea. Local currents, winds and tides move the seaweed into the Key Biscayne area where it mixes with seagrass removed locally from the ocean bottom and is deposited along the beach at high tide.

 

Amounts of these naturally occurring deposits vary by season. Residents and visitors are advised to expect large quantities during the summer/early fall. Hurricane season, from June to November, is seaweed season as well. The volume and duneward extent of the accumulations depends on the wave action and is influenced by currents, the strength and direction of wind and by tidal effects. Higher winds usually cause more seagrass, seaweed and other detritus to be deposited along the beach.

 

Mass accumulations of seaweed have affected Caribbean beaches since 2011 and indications are the deposits could increasingly affect South Florida beaches. The reasons behind these excess accumulations are being investigated by marine scientists.

 

Sargassum and seagrass are important, natural components of our marine ecosystem. They provide food and shelter and juvenile marine life and birds. 

Routine Seaweed Control via Beach Cleaning Program

Beach Raker, the Village's beach maintenance contractor, mechanically cleans the beach within the Village limits seven days a week. Operations begin at approximately 6:00 a.m. and end around 10-11:00 a.m. depending on the beach conditions and how many people are on the beach. During turtle nesting season, however, the beach contractor must wait until the morning turtle nest survey has been completed before any work can commence. The seaweed and seagrass are not hauled away but are buried at or below the mean high water line (MHWL).

 

At times of high winds, high tides, and high seaweed accumulations, the Village beach contractor faces challenging conditions. All the material may not be buried as a second tidal event occurs in the afternoon after morning work is completed.

 

Why Does the Village "Recycle" Seaweed and Seagrass?

Seaweed and seagrass are a vital part of the Village's beach ecosystem. The Village developed a beach management plan in consultation with Coastal Systems International (CSI), the Village's former long-time beach management consultant. The process of integrating the seaweed back into the sand by burying it at or below the MHWL is a major factor in preventing beach erosion. This is not only an essential process but a methodical one. The objective is to maintain the original profile of the beach by burying the seaweed at the wrack line. Seaweed is not hauled off the beach because of the amount of sand that is also removed with the seaweed during the hauling process. This leads to beach erosion over time, since a component of the beach ecosystem is removed and not replaced. Also, the disposal costs of seaweed are extremely high and make this process financially impractical.

Burying seaweed along the beach helps keep several erosion "hotspots" from losing more sand. Our present beach profile shows that nearshore currents in front of Key Colony and Island House can be 2 to 10 times stronger than along the rest of the beach. The result is that more sand and seaweed are deposited at these locations than along the rest of the oceanfront. At the same time these currents take away, or erode, sand from the beach in front of the Silver Sands, resulting in a cove where the beach width is less than to the north or south. Erosion of sand is also more severe further south in front of the Ocean Club. The large quantities of seaweed brought onshore in the summer/early fall have been extremely beneficial in helping "rebuild" the cove in front of the Silver Sands and in reinforcing the dunes in front of the Ocean Club. The net effect widens the sandy beach at locations where natural processes erode the beach more than in other areas.

 

Upon occasion, seaweed can be placed at the frontal area of the dunes. This provides the dune with nutrients to the sea oats and other dune plants that make up a healthy dune system. The unique c-shape and rough texture of the grass-like sea oat fronds capture windblown sand and deposit it among the dune plants, further building up the amount of sand within the system.

A healthy dune system benefits the beach and the Village in many ways. Robust vegetated dunes absorb wave energy and protect upland property in tropical storm events, and are a source of sand to the beach and nearshore areas after such events. Burying the seaweed on site removes the accumulations before they decompose and smell, and saves the Village money. Removal of this material from the beach would incur hauling and disposal expenses that are not financially feasible.

 

Need More Information?

The Village of Key Biscayne is committed to maintaining a healthy, attractive beach along the stretch of oceanfront within the Village limits. If you have any questions about the Village's beach management and maintenance policies, please contact Jessica Garcia, Division of Public Works, at jgarcia@keybiscayne.fl.gov or at (305) 365-8945.

 

 

 


"To provide a safe, quality environment for all islanders through responsible government."

 

© 2013 Village of Key Biscayne   |   88 West McIntyre Street   |   Key Biscayne, FL   |   33149   |   (305) 365-5511   |   feedback@keybiscayne.fl.gov

 

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