storm frequency, and (3) reduced rainfall. Historical and anecdotal evidence suggests a 
continuing shift over the past decades from a mixed habitat to an increasingly monospecific 
Thalassia community. Recolonization processes are establishing a more diverse mixture of 
habitats with the potential of enhanced secondary productivity in some areas. In 1992, a major 
dieoff expansion occurred in western Florida Bay. Further evidence of the effect of warm 
temperatures on Thalassia was found by Thorhaug et al. (1973) in the seagrass community near 
the Turkey Point Nuclear Power Plant cooling water canal in Biscayne Bay. Thalassia 
disappeared in areas of water 5°C above ambient, and declined by 50% in waters 3-4°C above 
ambient temperature. Environmental stress caused by climatic variations or changes in salinity 
may also make Thalassia more susceptible to disease (Thayer et al., 1994). Blackened, necrotic 
lesions on Thalassia leaves, caused by a previously undescribed species of the marine slime 
mold, genus Labyrinthula, are frequently associated with seagrass die-off in Florida Bay 
(Durako and Kuss, 1994). Sediment porewater sulfide concentrations in Florida Bay seagrass 
beds affected by the catastrophic mortality of Thalassia were considerably higher than those of 
seagrass beds elsewhere in Florida (Carlson et al, 1994). The high sulfide concentrations 
resulting from microbial degradation of dying Thalassia might have stressed adjacent seagrass 
beds. 
There appears to be a high potential for recovery of Thalassia beds. Thayer et al. (1994) 
postulate a sequence of steps in the recovery process. The alga Batophora oerstedii is the first 
colonizer, with replacement by other algal species, and subsequently Halodule wrightii, and 
eventually Thalassia. 
Seagrass habitats in western Florida Bay have been undergoing changes from monotypic 
Thalassia meadows to large landscapes of barren bottoms or to increasingly heterogeneous 
Thalassia meadows as a result of seagrass die-off patch formation. The cause of die-off is 
unknown but current hypotheses point to environmental stress making this seagrass susceptible 
to disease. The potential exists for colonization and recovery of these die-off patches but the 
sequence of events and the persistence of the recovery have not been evaluated. 
6.5. Sponge dieoffs 
The information in this section was found in Stevely et al. (1978). A historical account of the 
sponge fishery along the east coast of Florida can also be found in Shubow (1969). 
Up until the 1940s, the sponge fishery was one of the most valuable fisheries in Florida. 
However, a combination of disease, heavy harvesting pressure, and the introduction of 
synthetic sponges resulted in reduction of the industry to a small fraction of its former 
importance. Production in the Tarpon • Springs area, the traditional center for sponging in 
Florida, has declined to extremely low levels of harvesting activity. Dade County has emerged 
as the center of the existing sponge industry. Persistence of low level sponging activities in 
Florida for the last 30 yrs indicates that the sponge industry, as it is currently structured, 
will probably not return to former production levels. 
Sponges (phylum Porifera) are considered to be primitive in relation to other animal groups 
because of their simple structure and the fact that apparently no other group of animals has 
evolved from them. There is low level of cellular specialization in sponges. These organisms 
lack distinct organs and tissues, and interdependence sponges closely resemble colonies of 
independent single cell organisms with primitive characteristics. The phylum Porifera is 
divided into three classes based primarily on the composition and structure of the animals' 
skeletal framework. The skeleton may be composed of calcareous spicules, siliceous spicules, 
protein spongin fiber, or a combination of the latter two. These spicules are either calcium 
carbonate or silicon dioxide. The commercial sponges all come from one group, those having 
their skeleton made of spongin fibers only. Spongin is related chemically and physically to silk, 
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