Publication Date

2018-12-05

Availability

Open access

Embargo Period

2018-12-05

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology and Ecology (Marine)

Date of Defense

2018-10-31

First Committee Member

Diego Lirman

Second Committee Member

Elizabeth Babcock

Third Committee Member

Rolando Santos

Abstract

Seagrass communities display complex population dynamics that are presently poorly understood. While most studies of disturbance on seagrass habitats have focused on changes in biomass at small, quadrat-level scales, limited information is available on the impacts of disturbances on seagrass patch dynamics on a broad scale. In this study, a landscape approach based on remote sensing imagery and population modelling were applied to understand seagrass patch dynamics and forecast the fate of these important communities in Biscayne Bay, Miami, Florida, US. The seagrass communities of Biscayne Bay are especially influenced by the modifications of the Everglades watershed that has significantly changed the timing of freshwater deliveries and nearshore salinity patterns over the last 70 years. This research evaluated the historical influence of salinity on seagrass communities and how changes in salinity may cause seascape fragmentation by documenting the long-term population dynamics of seagrass habitats found adjacent and distant to freshwater canals. A positive outcome of this study is that the historical analysis covering > 70 years revealed remarkable persistence of seagrass cover even in habitats that were modified by the construction of freshwater canals. Fragmentation rates of the seagrass patches varied spatially and temporally but were higher in sites adjacent to canals compared to sites removed from these influences. Furthermore, there was a clear trend in mortality rates in relation to the size of seagrass patches, with the smallest patches undergoing 57% annual mortality on average. Model simulations based on observed patch dynamics suggest that seagrass meadows can persist as long as the recruitment of new patches compensates for patch fragmentation. The combination of higher fragmentation rates and the higher mortality of smaller seagrass patches in habitats exposed to pulses of low salinity raises concern for the long-term persistence of seagrass meadows in nearshore urban habitats of Biscayne Bay that are presently targets of Everglades restoration. The combined remote sensing and population modelling approach used here provide evaluation and predictive tools that can be used by managers to track seagrass status and stress-response at seascape levels not available previously for the seagrasses of South Florida.

Keywords

Fragmentation; population dynamics; seagrass; landscape approach; population modelling; spatial analysis

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