We examined the response of demographic, morphological, and chemical parameters of turtle grass (Thalassia testudinum), to much-higher-than-normal rainfall associated with an El Niño event in the winter of 1997-1998. Up to 20 inches of added rain fell between December 1997 and March 1998. triggering widespread and persistent phytoplankton blooms along the west coast of Florida. Water-column chlorophyll concentrations estimated from serial Sea WiFS imagery were much higher during the El Niño event than in the previous or following years, although the timing and magnitude of phytoplankton blooms varied among sites. Seagrass samples collected in 1997, 1998, and 1999 provided an excellent opportunity to test the responsiveness of Thalassia to decline and subsequent improvement of water quality and clarity in four estuaries. Using a scoring technique based on temporal responsiveness, spatial consistency, and statistical strength of indicators, we found that several morphological parameters (Thalassia shoot density, blade width, blade number, and shoot-specific leaf area) were responsive and consistent measures of light stress. Some morphological parameters, such as rhizome apex density, responded to declines and subsequent improvement in water clarity, but lacked the statistical discriminating power necessary to be useful indicators. However, rhizome sugar, starch, and total carbohydrate concentrations also exhibited spatially and temporally consistent variation as well as statistical strength. Because changes in shoot density, as well as water clarity, affect rhizome carbohydrate levels, a composite metric based on Thalassia shoot density and rhizome carbohydrate levels together is probably more useful than either parameter alone as an indicator of seagrass health.

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composite metric serial sea wifs imagery chlorophyll statistical strength of indicators water clarity light scoring technique shootspecific leaf area muchhigherthannormal rainfall demographic morphological and chemical parameters water quality turtle grass thalassia testudinum phytoplankton blooms temporal responsiveness spatial consistency shoot density blade width blade number rhizome sugar starch and total carbohydrate concentrations seagrass health discriminating

Paul R, Carlson Laura A, Yarbro Kevin, Madley Herman, Arnold Manuel, Merello Lisa, Vanderbloemen Gil, McRae Michael J, Durako,.Effect of El N?no on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators.. 81 (1-3),393-408.

Paul R, Carlson Laura A, Yarbro Kevin, Madley Herman, Arnold Manuel, Merello Lisa, Vanderbloemen Gil, McRae Michael J, Durako,"Effect of El N?no on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators." 81

Paul R, Carlson Laura A, Yarbro Kevin, Madley Herman, Arnold Manuel, Merello Lisa, Vanderbloemen Gil, McRae Michael J, Durako,"Effect of El N?no on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators."