concentrations. Significant differences were found among basins for concentrations of 
total free amino acids, glutamic acid, proline, and arginine. Glutamine and proline also 
exhibited significant differences among die-off zones. Current data suggest (1) hypoxic 
stress may play an important role in the die-off process, and (2) physiological assays 
may be dramatically affected by tissue heterogeneity. 
1989 0 
Windom, H. L., S. J. Schroop, F. D. Calder, J. D. Ryan, R. G. Smith, L. C. Burney, F. G. f 
Lewis, and C. W. Rawlinson (1989) Natural trace metal concentrations in estuarine and 
coastal marine sediments of the southeastern United States. Environ. Sci. Technol. . 
23:314-20. 
Over 450 sediment samples from estuarine and coastal marine areas of the 
southeastern United States remote from contaminant sources were analyzed for trace 
metals. Although these sediments are compositionally diverse, As, Co, Cr, Cu, Fe, Pb, 
Mn, Ni, and Zn concentrations covary significantly with Al, suggesting that natural 
aluminuosilicate minerals are the dominant natural metal bearing phases. Cadmium and 
Hg do not covary with Al apparently due to the importance of the contribution of natural 
organic phases to their concentration in sediments. It is suggested that the covariance 
of metals with Al provides a useful basis for identification and comparison of 
anthropogenic inputs to southeastern U.S. coastal/estuarine sediments. By the use of 
this approach sediments from the Savannah River, Biscayne Bay, and Pensacola Bay 
are compared. Samples were collected in the Ten Thousand Islands, Whitewater Bay, 
and Florida Bay. 
1989 - 1990 
Carlson, P. R., M. J. Durako, T. R. Barber, L. A. Yarbro, Y. deLama, and B. Hedin (1990) 
Catastrophic mortality of the seagrass Thalassia testudinum. Annual completion rep. Florida 
Dept, of Enviromental Regulation, Florida Marine Research Institute, St. Petersburg, FL. 51 
PP- 
Rapid and widespread mortality of the seagrass Thalassia testudinum is occurring in 
Florida Bay at the southern tip of the Florida Peninsula. This study was performed to: 
(1) quantify the current extent and dynamics of this die-back, (2) assess the recovery 
potential of the die-back sites, and (3) determine the cause(s) of the die-back. Sampling 
was performed in Johnson Key and Rabbit Key Basins and Ranking Lake in the Bay during 
1989 - 1990. Quantitative bimonthly sampling monitored temporal and spatial 
variability in Thalassia's morphometric characteristics. Short-shoot densities, leaf 
lengths, and leaf area indices decreased significantly along gradients from visually 
healthy beds to die-back patches. Leaf numbers per short-shoot were usually highest in 
die-back patches reflecting very low plastochrone intervals (as short as 4-6 days). 
Leaf numbers were lowest in October and December as a result of normal summer leaf 
die-back. Bimonthly sampling of sediment sulfide and Thalassia rhizome metabolites 
revealed that porewater sulfide levels were highest in October, a period of peak 
intensity of die-back. Sulfide concentrations at this time exceeded 2 mM; a level which 
may cause cytotoxic effects. This suggests that sulfide may play a synergistic role in 
the die-back phenomenon. Rhizome ethanol concentrations were significantly affected 
by tissue type, sample interval, and basin, but were not significantly different between 
zones and times of day. Rhizome alcohol dehydrogenase activity (ADH) was 
significantly related to sample date and basin, but effects of zone and tissue type on 
ADH were not significant. ADH activities are not specific indicators of die-back induced 
stress, but they are useful as an index of cumulative, chronic hypoxic stress from all 
sources. No amino acids exhibited significant zone effects which might indicate 
disruption of normal metabolism by the die-back process. An assessment of the roles of 
vegetative and sexual reproduction in the recovery potential of die-back sites revealed 
335 
