few organisms, especially outside of tropical Caribbean waters. In addition to 
contributing to local food webs, detached seagrass blades are often exported great 
distances and serve as food sources hundreds of kilometers from their source beds. 
1987 - 1988 
Zieman, J. C., J. Fourqurean, M. B. Robblee, M. Durako, P. Carlson, and G. Powell (1988) A 
catastrophic die-off of seagrasses in Florida Bay and Everglades National Park. EOS Trans. . 
69:111 1. 
[ABSTRACT ONLY.] Over the past year, Florida Bay has experienced a major die-off of 
seagrasses and benthic macrophytes totaling several thousands of hectares. Dead areas 
range from patches 0.5 m across to contiguous, thousand hectare dead zones and 
include all benthic vegetation. There are four major distressed areas, three in the 
west-central bay and one in the east. None are directly adjacent to the Florida Keys. 
The areas affected are primarily basins and the sides of basins, all with very dense 
seagrass (primarily Thalassia) cover and reduced circulation. Abnormal amounts of 
dead leaves were first noted in August 1987. By July-August 1988, the phenomenon 
appears to be slowly enlarging, although there is definite evidence of regrowth in some 
affected areas. Surviving and recolonizing shoots possess unique morphologies, 
including short internodal distances and abnormally high leaves/shoot (up to 17). Pore 
water sulfide concentrations were about two times higher in dead areas as opposed to 
nearby, apparently dead areas (2.14 vs 1.32 mmol). Several hypothetical mechanisms 
responsible for the die-off are being explored including (I) abnormally high 
temperatures in summer 1987, (2) extreme salinities, and (3) disease, among other 
possibilities. At the present time the area is experiencing abnormal epiphyte and algal 
growth, apparently due to the release of nutrients from the nutrient rich barren 
sediments and the thousands of metric tons of decaying seagrass. 
1987 - 1989 
Fourqurean, J. W., J. C. Zieman, G. V. N. Powell (1992) Relationships between porewater 
nutrients and seagrasses in a subtropical carbonate environment. Mar. Biol. . 114:57-65. 
The primary source of nutrients for seagrass growth is considered to be sediment 
porewater. Porewater nutrient concentrations were measured in 18 seagrass beds 
across Florida Bay during the summers of 1987 and 1988. Concentrations of nutrients 
in porewater varied widely, with median values of 0.34 pM for soluble reactive P 
(SRP) and 78.6 nM for NH 4 + . SRP and NH 4 + concentrations were positively correlated. 
Due to spatial heterogeneity, there were no apparent trends with sediment depth (down 
to 40 cm) in the porewater nutrient concentrations. The SRP concentration of the 
porewater was highest in areas supporting Halodule wrightii, intermediate in areas of 
Thalassia testudinum, and lowest in sediments without seagrasses. There was no 
similar relationship with NH 4 + . Porewater SRP, but not NH 4 + , was significantly 
correlated with total seagrass standing crop. Elemental content (both N and P) of green 
leaves of T. testudinum was a function of the concentration of the nutrients in the 
porewater. Standing crop of T. testudinum was correlated with phosphorus content, but 
not with N content, of the seagrass leaves. The results support the hypothesis that 
sediment porewaters are the most important source of nutrients for seagrass growth. 
In the Bay's subtropical carbonate environment, the availability of P in the porewater 
limits the development, and controls the species composition of seagrass. 
1987 - 1989 
Fourqurean, J. W., J. C. Zieman, G. V. N. Powell (1992) Phosphorus limitation of primary 
production in Florida Bay: evidence from C:N:P ratios of the dominant seagrass Thalassia 
testudinum. Limnol. Oceanoar. . 37( 1): 162-71. 
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