THORHAUG, ANITRA1* and HAROLD WANLESS2. 1658 NE 70 ST, Miami, Fl. 33138; 21231 Genoa ST, Coral Gables, FL 33134. - The role of hurricanes, tornados and gale force winds in seagrass distribution in subtropical and tropical nearshore waters.
The role of high-energy periodic wind events on seagrasses has been
chiefly anecdotal. Sites in Biscayne Bay, FL and the Laguna Madre, TX
are compared for 4 study sites. Two sites in Laguna Madre were
investigated for seagrass test plots, sediment cores, vegetative
mapping and aerial photography over a 4-year period, with a
large-scale seagrass restoration (14.7 acres at one site and 60 acres
at the second site) carried out in 1999. Hurricane Bret hit the
60-acre site two weeks after monitoring. A post-hurricane monitoring
occurred. Aerial photos were subjected to analysis, available from
1996, 1998, 1999 post-hurricane and 2000. A second 14.7 acre Laguna
Madre site was hit by a tornado after one half was restored in March
1999. Two lines of craters occurred which we documented by markers.
The Biscayne Bay sites (in the Central Bay) had been mapped and ground
truth data taken with sediment samples over years prior to a January
1983 hurricane force wind (off the south end of Key Biscayne).
Morphological changes to the existing vegetation and corals were
recorded. The second site (3 miles away) had been by examining aerial
photos over a period of 20 years was restored with the seagrass
Halodule wrightii during the summer, 1982, with 68% survival pre-gale
in Fall 1981. Post-gale monitoring of seagrass beds showed the almost
hurricane force wind caused substantial damage to the restoring
seagrasses. Results of the four sites and comparisons of the
vegetative cover, sediment and background vegetation will be discussed
with data. Conclusions: 1.) Tornados can disrupt seagrasses leaving
effects on for years; 2.) Gale force winter winds and hurricanes can
alter shallow seagrass beds; 3.) Recuperation and re-growth after
storm events can vary as to species and dissemule availability.
Key words: Biscayne Bay FL, hurricane, Laguna Madre TX, seagrass, sediment, tornados