HCNSO Student Theses and Dissertations

Defense Date

5-4-2018

Document Type

Thesis

Degree Name

M.S. Marine Biology

First Advisor

Dr. Brian Walker, PhD

Second Advisor

Dr. Charles Messing, PhD

Third Advisor

Prof. John Reed, M.S.

Abstract

The deep-sea is a vast and relatively sparsely characterized domain. As little as 0.01% of deep-sea benthic habitats have been characterized in detail. Characterizing the distribution of organisms and environmental components of the deep-sea is pivotal to the creation and implementation of successful resource management. Benthic habitat maps are a good method to inventory and characterize deep-sea habitats. Recent advances in technology, such as multibeam sonar and remotely operated vehicles (ROVs), have allowed for greater understanding of these ecosystems. As it is difficult and expensive to collect data deep-sea benthic community composition, environmental surrogates of biological data would be economically beneficial. Ideally, a surrogate is an easily-measured abiotic indicator that greatly influences benthic community composition. The quality of a surrogate can be extrapolated to represent the quality of benthic habitat. The Miami Terrace is a deep-sea ecosystem that has begun to be explored and characterized. Previous studies noted that community compositions vary with broad-scale geomorphology on the Miami Terrace. This study addresses a swath of data collected from the Miami Terrace to determine if geomorphology in high resolution bathymetry could serve as a viable surrogate to biological data for the initial characterization of benthic habitats on the Miami Terrace. Data from cable impact assessment surveys for the South Florida Ocean Measurement Facility (SFOMF) and the Department of Energy were utilized in this study. Images from these surveys were analyzed to generate and detail twelve transects across a section of the Miami Terrace. This cross section of the terrace had previously been sectioned into distinct geomorphologic zones (Messing et al., 2012). The geomorphologic zones assessed in this study were High Slope Inner Terrace (HSIT), Low Slope Inner Terrace (LSIT), High Slope Outer Terrace Platform (HSOTP), Low Slope Outer Terrace Platform (LSOTP), High Slope Outer Terrace Ridge (HSOTR), and Low Slope Outer Terrace Ridge (LSOTR). Images from these transects were analyzed to generate percent cover and community data. This data includes overall organism density, species richness, and an inventory of all organisms greater than 4 cm identified to the lowest taxonomic level possible. This data was taken in concert with previously collected environmental data (e.g. depth, slope, and geomorphology) and subjected to multivariate statistical analysis. Patterns in organism density across the transects align with the progression of the transects by slope and geomorphologic region. Depth was seen to increase from Inner Terrace to Outer Terrace Platform. The Outer Terrace Ridge exhibited an increase in the percent cover of hardbottom habitat; which is preferential for many organisms. This corresponded to a shift in the organism density of multiple Cnidarians and Poriferans. In particular, the density of stylasterids and several sponges increased towards the Outer Terrace Ridge. One High Slope Inner Terrace transect juts into the Outer Terrace Platform, and it was more similar to Outer Terrace Platform transects than those of the Inner Terrace. This suggests that area of Inner Terrace jutting into the Outer Terrace Platform may need to be reassigned as Outer Terrace Platform. Analysis of variance by region and slope yielded that the density of multiple species varies with geomorphology across the study area, and high slope areas had significantly higher species richness than areas of low slope. These results support that geomorphology could serve as a surrogate for the Miami Terrace; however, it is likely a combination of geomorphology and another environmental factor (e.g., percent cover substrate or depth) would better serve to predict distribution of species on the Miami Terrace. The results of this study support that geomorphologic region, slope, depth, and percent cover of substrate can be used to determine different deep-sea habitats on the Miami Terrace. The influence of geomorphology on organism densities was varied, and thus its predictive capacity and efficacy as a surrogate remains limited. Nevertheless, the necessity for ecological baselines to guide management decisions is greater than the uncertainty associated with the use of geomorphology as a surrogate on the Miami Terrace.

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