Publication Date

2014-12-12

Availability

Embargoed

Embargo Period

2016-12-11

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2014-11-07

First Committee Member

Diego Lirman

Second Committee Member

David Die

Third Committee Member

Joe Serafy

Fourth Committee Member

Shouraseni Sen Ro

Fifth Committee Member

Simon Pittman

Abstract

My dissertation adopted concepts and spatial tools of seascape ecology, the marine counterpart of landscape ecology, to understand the broad-scale structural attributes that make submerged aquatic vegetation (SAV) seascapes resilient to anthropogenic disturbances, drivers of fauna community structure, and productive fisheries habitats. My research was designed to address the relative and interrelated ecological effects of broad-scale changes in SAV habitat amount (habitat loss) and configuration (fragmentation). SAV seascapes in nearshore areas of Biscayne Bay have been subject to constant anthropogenic disturbances associated to freshwater pulses from canals over the last 50 years; thus, these seascapes served as a model system to link water management practices, seascape transformation (e.g., habitat loss and fragmentation), and to evaluate cascading effects on marine fauna. First, I performed a long-term analysis of SAV seascape characteristics using archived black-white aerial photographs, from 1938 to 2009, to assess the spatio-temporal trends of SAV habitat fragmentation independently of habitat loss within Biscayne Bay’s nearshore habitats. Habitat loss and fragmentation were significantly higher along the shoreline compared to offshore seascapes removed from freshwater influences. All sites exhibited higher fragmentation in 2009 compared to 1938, and while areas adjacent to canals had significantly higher SAV cover, they still experienced wide fluctuations in cover and fragmentation over time. Two organism-habitat relationship studies were designed and implemented to explore the nature of the ecological responses to SAV seascapes. First, I compared fish and crustacean community assemblages and diversity between spatially continuous and fragmented SAV seascapes. Fragmented seascapes supported significantly higher species richness of fish and crustaceans and higher biomass of carnivorous fishes than did continuous seascapes. The community patterns were also influenced by salinity, indicating that both water quality and spatial properties of SAV seascapes play an important role in structuring faunal communities. Second, I applied multivariate non-linear models to evaluate patterns of abundance of the most common fish and shrimp species to document species-specific responses to SAV seascape characteristics, and to determine whether habitat amount and configuration thresholds exist in the response of organisms to seascape structure. The amount of SAV habitat and its patch configuration (and the interactions between these two metrics), were the most influential predictors of faunal abundance, and outperformed fine-scale habitat characteristics such as seagrass cover and canopy height as predictors of faunal responses. Abundance thresholds were identified for all species in response to patch complexity and habitat composition and configuration which help to determine the minimum amount of habitat and maximum level of fragmentation that could sustain fish and crustacean populations. Finally, field experiments using baited remote underwater video surveys (BRUVs) and tethering with Farfantepenaeus duorarum (pink shrimp) were designed to test whether predation and predation-risk effects are key mechanisms generating patterns in fish and crustacean abundance in relation to habitat amount and configuration. Both BRUVS and tether experiments identified higher predation risk at boundaries of the seagrass meadows (at mangrove-seagrass edges, and seagrass seaward edges). Based on allocation time and pecking rate, it was evident that habitat shifts occur in response to seascape spatial properties and risk of predation. In conclusion, the transformation of the SAV seascape in Biscayne Bay has been induced mainly by salinity patterns associated with freshwater inflow inot the bay. Moreover, seascape characteristics and transformations directly linked to the abundance and distribution of SAV-associated fish and crustacean assemblages. These patterns are most likely attributed to the roloe that seascape play in species interactions and trophic dynamics. Thus, my work showed how seascape ecology concepts could be used to evaluate questions about ecological dynamics and patterns induced by anthropogenic disturbances and the spatial transformation of essential fish and crustacean habitats.

Keywords

seagrass; landscape ecology; habitat loss and fragmentation; GIS; disturbance ecology; predation

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