Seagrasses Fact Sheet

 

 

What are seagrasses?

·        they are flowering plants that live in shallow, marine waters

·        like land plants, seagrasses have roots, leaves, flowers, pollen and seeds

·        like land plants, seagrasses obtain most of their nutrients from sediments (whereas algae get most of their nutrients from the water column)

 

 

Why are seagrasses considered to be so important?

·        they provide habitat and nursery areas for estuarine animals (75% of the economically important marine fish in Florida rely on estuaries directly!)

·        seagrasses enhance water quality by removing nutrients

·        they enhance water quality by stabilizing the sediments with their roots and rhizomes, which are horizontal, underground stems

·        seagrasses help keep the water column clear of particulate matter as the blades reduce the energy of the waves and currents moving through the beds (this reduces erosion and reduces the resuspension of fine particles)

·        like rain forests and salt marshes, seagrass meadows are among the most productive ecosystems in the world

 

 

Seagrasses are used to indicate the health of an estuarine system.  They are sensitive to changes in water quality, so a decline in seagrass coverage may be a sign of decreasing water quality.  For instance, if stormwater runoff carries lots of sediment and nutrients into the estuary, then the amount of light reaching the seagrasses diminishes.  This may cause the seagrasses to die, especially in deeper waters.  Since the amount of light reaching the seagrasses is the main factor that determines whether seagrasses will grow or not, it is crucial to reduce the amount of pollution entering our bay.  Too much suspended sediment blocks the sunlight, and the input of nutrients produces phytoplankton (microscopic organisms suspended in the water column), and algal blooms and an increase in epiphytes (algae that grow ON the seagrass blades).  All these also block the sunlight.

 

 

What influences seagrass growth?

·        the amount of light reaching the blades

·        the type of sediment in the estuary

·        the type and abundance of nutrients in the sediments

·        extreme weather events

·        the salinity of the water

·        prop scars and stormwater runoff carrying herbicides may reduce seagrass growth

 

 

How has seagrass coverage changed in St. Andrew Bay over the past 30 years?

·        using aerial photos that were digitized by the USGS, we see a 17% decline in seagrass coverage

·        in West Bay alone, we see a 49% decrease in seagrass coverage

·        using aerial photos taken by FMRI in 1994, we see that more than 50% of the seagrass beds in St. Andrews Bay have been scarred by boat propellers

 

 

How should we interpret these facts?

·        We could be seeing natural decreases in seagrass coverage.  Maybe in 30 years, we’ll see a very large increase.  We do not know if seagrass coverage follows a natural cycle of increases and decreases.

·        These losses might indicate that our estuarine system is being stressed.

 

 

What can we do to protect seagrasses?

·        start a seagrass monitoring program

·        reduce the amount of prop scarring by educating boaters

·        reduce the amount of pollution entering the bay by cleaning up point source pollution and reducing stormwater runoff into the bay

·        reduce stormwater runoff by establishing buffer zones along the shoreline of the bay and by reducing the amount of impervious surfaces we place on the land

·        reduce the amount of pesticides and fertilizers used on our lawns and reduce the number of septic tanks in our area

 

 

How do we monitor seagrasses?

  • transects, or lines extending from the shoreline to the deep edge of the seagrass beds, are established in different locations of the bay
  • volunteers go out in teams
  • one person drives the boat
  • another person records the depth of the water every 10 meters
  • a third person dives along a rope that has been extended from the deep edge of the bed to the shore and records the following information every 10 meters

·        height and width of the leaves

·        percent cover

·        species composition

·        if equipment and time permits, a diver can videotape the seagrasses along the transect so that a visual record is also made