Diego Lirman, Jiangang Luo, John Wang

Assessment of the Effects of the Everglades Restoration Project and Climate Variability on the Growth and Survivorship of Seagrasses and Sponges of Biscayne Bay

Diego Lirman, Jiangang Luo, John Wang

University of Miami, Miami, FL

Wendell P. Cropper Jr.,

University of Florida, Gainesville, FL

An integrated modeling framework developed by CMEA scientists was used to translate climate change and water management scenarios into ecological changes for biological endpoints of Biscayne Bay. In this modeling framework, the South Florida Water Management Model was linked to the Biscayne Bay hydrodynamic model to simulate salinity patterns within Biscayne Bay under different climate change and Everglades restoration scenarios. The output from the Biscayne Bay hydrodynamic model, expressed as daily salinity values, provided direct input into the SEASCAPE model of benthic communities of Biscayne Bay. The spatially explicit SEASCAPE model is comprised of over 100,000 cells (100 x 100 m) and contains several biological components, including the seagrass growth model and a sponge population model that will be described in this presentation.

The seagrass growth model simulates above-ground biomass of the three most common seagrass species (turtle grass (Thalassia testudinum), shoal grass (Halodule wrightii), and manatee grass (Syringodium filiforme)) within Biscayne Bay. Daily growth is simulated as a species-specific maximum growth rate modified by light availability, temperature, sedimentation, nutrient concentrations, and salinity. The sponge population model is a stage-based matrix population model of the commercially harvested Glove Sponge (Spongia graminea). The sponge model assumes that salinity limits population size as exposure to fresh water is known to damage marine sponges. Output from the hydrodynamic model is used to determine the number of days sponge populations are exposed to salinities below threshold values under different simulation scenarios.

Major changes in canal, overland, and groundwater flows into coastal bays can result from modifications to water management practices and natural interannual variability in precipitation. These changes in freshwater flows can lead to significant differences in the salinity fields within Biscayne Bay as simulated in this project. Areas where canal influences are prevalent (i.e., central bay) can experience significant reductions in mean salinities for extended periods of time under “wet” scenarios, while areas with restricted circulation (i.e., southern bay) can experience periods of hypersalinity (> 40 ppt) under “dry” conditions. In contrast, minor changes in salinity patterns were simulated for those areas in eastern Biscayne Bay where oceanic influences prevail.

Our initial simulations indicate that increased freshwater delivery to Biscayne Bay can damage sponge populations in western Biscayne Bay by increasing the frequency of low-salinity events. Similarly, reduced salinity can influence growth and abundance seagrass communities. Species such as Thalassia testudinum that are more susceptible to reduced salinity could be lost or out-competed from present locations, and replaced by less-susceptible species like Halodule wrightii.

Diego Lirman, University of Miami, 4600 Rickenbacker Causeway, Miami, FL33149

Phone: 305-361-4168, Fax: 305-361-4600,

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