Joan A. Browder

The natural South Florida system II: Predrainage ecology

The goal of the South Florida restoration process is to reestablish a sustainable ecological system that approximates the predrainage system (i.e., the system that existed before canals and water control structures were built). A critical step in the restoration process is to describe the predrainage system with sufficient detail to capture the essential landscape features (e.g., space, connectivity, patterns) that gave the region its defining character and supported its natural abundance and diversity of plants and wildlife.A previous attempt at reconstruction of predrainage (circa 1870) vegetation patterns covered only the Everglades (Davis et al., 1994) but introduced a concept of landscape mosaics that should be extended to South Florida. We propose 16 landscape units that include freshwater landscapes, upland landscapes, coastal wetlands, and estuaries (particularly Florida and Biscayne Bays), the Florida Keys and Reef Tract, and the Inner Southwest Florida Shelf.The predrainage area, because of its enormous size, supported a landscape heterogeneity that was advantageous to animals with several distinct habitat-related life strategies. Five species have been selected to illustrate different dependencies on landscape patterns in predrainage South Florida: wood stork (Mycteria americana), American alligator (Alligator mississippiensis), snail kite (Rostrhamus sociabilis), Cape Sable seaside sparrow (Ammodramus maritimus mirabilis), and pink shrimp (Penaeus duorarum). As individuals or as populations, these animals operated across several spatial and temporal scales. The predrainage systems large spatial extent and complex hydropatterns allowed wood storks and other animals with large feeding ranges to take advantage of the strongly seasonal rainfall pattern, while at the same time providing a refuge somewhere in the system for survival of all other species. Landscape heterogeneity and large spatial extent promoted the regions natural wildlife abundance and species diversity.

Environmental management scenarios: Ecological implications

The measure of whether a management scenario is capable of establishing regional-scale ecosystem sustainability is the degree to which it recovers the historical characteristics of the regional landscape mosaic. This study examines the ability of alternate management scenarios to recover the defining ecological features of the Everglades and South Florida landscape. Five conceptual scenarios are evaluated for recovering and sustaining the ecological characteristics of the wetland systems in South Florida. First, the regional-scale physical characteristics are identified that created and supported the major organizing and driving forces in the predrainage Everglades and Big Cypress basins. Eight hypotheses are proposed to explain how human-caused modifications to these defining characteristics have been responsible for the substantial level of ecological deterioration that has been documented in South Florida wetlands during the last century. The restoration scenarios are evaluated on their proposed ability to correct the physical and biological problems identified by the hypotheses. Our assessment of the five scenarios shows that all would improve the problems addressed by the eight hypotheses, as all could more effectively move increased volumes of water across broader expanses of contiguous wetlands than do existing management programs. This would result in longer hydroperiods over larger areas, reflecting historical patterns. Two of the scenarios would be successful in increasing flows into Florida Bay and the Gulf coast estuaries because removing internal structures increases the spatial extent of the upstream areas that could be devoted to natural hydropatterns.The benefits of eastern boundary buffer zones include improved flow into the Taylor Slough basin. Using Lake Okeechobee as a site for increased water storage, followed by the addition of eastern buffer zones and portions of the Everglades Agricultural Area, would produce increased flexibility in providing the storage capacity required to meet sustainability goals. Scenarios with maximum areas of buffer not only are more successful in reducing groundwater seepage losses to the east but also are more likely to reduce the level of nutrients and other contaminants entering the natural wetlands.

Influence of Temperature and Salinity on Growth, Survival, and Biomass Productivity of Postlarval and Early Juvenile Pink Shrimp Farfantepenaeus duorarum (Burkenroad 1939)

ABSTRACT An investigation was conducted of the combined effect of salinity and temperature on growth, survival, and biomass productivity of postlarval and early juvenile pink shrimp Farfantepenaeus duorarum (Burkenroad 1939) produced from a single spawning event. The study used a factorial block design consisting of three salinity treatments (15, 35, and 55), each replicated, within three temperature treatment (22°C, 27°C, and 32°C) water baths. The study was divided into two phases: postlarval (first 28 days) and early juvenile (second 28 days). Growth was assessed every 7 days throughout the experiment by measuring carapace length (CL) and wet weight (WWT) of 15 randomly selected shrimp from each temperature/salinity replicate tank. After the first study phase, survival was assessed and experimental aquaria were reset with 30 randomly selected shrimp from the same temperature—salinity replicates. Survival was assessed again at the end of the early juvenile phase. The effect of treatments was evaluated by average growth (average finalWWT), survival, and average final biomass production. Exponential growth rates (CL andWWT) and temperature physiological coefficients (Q10) were also computed. Effects of temperature and salinity on growth and survival were variable, and no significant interaction among the treatment factors was observed. Biomass production increased consistently with temperature (postlarval, P > 0.0001; early juvenile, P < 0.0001) and decreased at the highest salinity (55; postlarval, P = 0.0140; early juvenile, P < 0.0001). Significant reductions in all performance outcomes except postlarval growth (P > 0.05) were observed at the high salinity of 55. The response of growth to salinity was not significant until the early juvenile treatment phase, whereas the effect of temperature on growth was significant during both phases. Hypersalinity (salinity, 55) had a detrimental effect on performance outcomes; however, performance outcomes at salinities of 15 and 35 were comparable. These results have implications for the natural productivity of pink shrimp in Florida Bay, where conditions are often hypersaline.