Modeling Algae Stressors

The Effects of Environmental Stressors on the Dynamics of Three Functional Groups of Algae in Thalassia testudinum Habitats of Biscayne Bay, Florida: a Modeling Approach

The effects of stressors related to canal discharges on near-shore, shallow-water tropical macroalgae occurring in Thalassia testudinum (turtlegrass) ecosystems were investigated. Three functional groups of macroalgae (drift algae, rhizophytic algae, and seagrass epiphytes) contribute to seagrass system structure and function. Drift algae and epiphytes have the potential to shade seagrasses under conditions of elevated water-column nutrients. Within Biscayne Bay, seasonal and spatial changes in the macroalgal community may be related to canal discharges. Drift algae dominated in canal influenced sites, while rhizophytic algae were dominant in oceanic sites. Epiphytes were found in both conditions with filamentous species in canal sites, whereas calcareous forms dominated in oceanic sites.

The physiological responses by the macroalgae to environmental variables including light, temperature, salinity, nutrients, and hydrodynamic regime were investigated. Temperature was found to drive seasonal changes in abundance, whereas salinity and nutrients were important determinants of the spatial distribution of the three functional groups within the Bay. Low-salinity stress from canal discharges had a negative impact on growth, while nutrient addition (primarily ammonia-nitrogen) had a stimulating effect. Bay-wide tidal circulation patterns were found to affect the distribution of drift algae, with accumulation occurring along the mainland coastline, and removal of drift algae occurring in the high-flow conditions typical of the oceanic inlets.

A simulation model of algal productivity was developed to augment a pre-existing primary production model for seagrass systems. The algal productivity models were modified and parameterized with data from field and experimental investigations in Biscayne Bay, as well as from pre-existing literature data available for similar tropical seagrass systems. The models were validated for a select number of sites (canal, sheet-flow and oceanic) representing the range of environmental regimes present in Biscayne Bay. Predicted simulation results agreed closely with the observed field data for both drift and rhizophytic algae, but less so for the epiphytes. In canal-influenced portions of the Bay, rhizophytic algae had reduced biomass because of low-salinity stress, drift algae bloomed under favorable temperature conditions because of the high nitrogen loadings, and filamentous epiphytes were favored over calcareous forms.

Seagrass Coring - CMEA style

Seagrass (Thalassia testudinum) cores, 30cm diameter, were collected from Bear Cut, near Key Biscayne, to stock nine experimental mesocosms at the University of Miami's Rosenstiel School of Marine and Atmospheric Sciences.

Publications from this research:

Biber, P.D. 2002. The Effects of Environmental Stressors on the Dynamics of Three Functional Groups of Algae in Thalassia testudinum Habitats of Biscayne Bay, Florida: A Modeling Approach. Ph.D. Dissertation, University of Miami, Coral Gables, FL. 367p.

Lirman, D. and P.D. Biber. 2000. Seasonal dynamics of macroalgal communities of the Northern Florida Reef Tract. Botanica Marina 43: 305-314.

Irlandi, E.A., B. Orlando, S. Macia, P. Biber, T. Jones, L. Kaufman, D. Lirman and E. T. Patterson. 2002. The influence of freshwater runoff on biomass, morphometrics, and production of Thalassia testudinum. Aquatic Botany 72:67-78.

Lirman, D., B. Orlando, S. Macia, D. Manzello, L. Kaufman, P. Biber, and T. Jones. 2003. Coral communities of Biscayne Bay, Florida and adjacent offshore areas: Diversity, abundance, distribution, and environmental correlates. Aquatic Conservation 13:121-135.

Biber, P.D., M.A. Harwell, and W. P. Cropper, Jr. 2004. Modeling the dynamics of three functional groups of macroalgae in tropical seagrass habitats. Ecol. Modeling 175:25-54.

Irlandi, E.A., B.A. Orlando, and P.D. Biber. 2004. Drift algae-epiphyte-seagrass interactions: potential positive impacts of drift algae on seagrass. Mar. Ecol. Progr. Ser. 279:81-91.

Biber, P.D., Irlandi, E.A. 2006. Temporal and spatial dynamics of macroalgal communities influenced by an anthropogenic salinity gradient. Aquatic Botany 85:65-77

Biber, P.D. 2007. Transport of drifting macroalgae (Rhodophyta) is strongly influenced by flow velocity. Marine Ecology Progress Series 343:115-122

Biber, P.D. 2007. Hydrodynamic transport of drifting macroalgae (Rhodophyta) through a tidal cut. Estuarine Coastal and Shelf Science 74:565-569