Date of Award

7-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

Community composition and distribution of coral species in the mesophotic zone off the South Texas Coast were cataloged from five relict mid-shelf coral algal banks referred to as the South Texas Banks including, from north to south, Baker, Aransas, Dream, Blackfish Ridge, and a previously undescribed reef thereto referred as Harte Bank. Hermatypic corals flourished at these sites, approximately 21,000 to 12,000 years BP in the late Pleistocene to early Holocene epochs. Today these reefs are located 97 km offshore and protrude to heights ranging 58 to 83 m below the sea surface with portions extending 20 to 30 m beneath the seafloor. Reef coral taxa were quantified from Remotely Operated Vehicle (ROV) video collected during the September 2012 Schmidt Ocean Institute R/V Falkor cruise. Multiple ROV transects were conducted across each of the relic banks generating ~36 h of video footage. Coral taxa densities (individual/m2) were estimated from discrete 30 sec video segments. Bank coral communities varied significantly (F= 4.18, df=4, 222, p=0.001) across banks and topography breaks (slope and terrace). Pairwise testing indicated significant differences among all terrace communities (P<0.001) with fewer differences among slope communities. Despite statistical differences, coral communities were markedly similar ranging 58 to 70% among terraces and 49 to 76% among slopes. Pairwise testing of topography breaks within banks indicated that all slope and terrace communities were significantly different for the exception of Harte Bank, wherein terrace depths were similar to slope depths of other banks. Variation in coral communities among the banks were highly correlated ( >0.95) to the geographic and geomorphic features including bank area, rugosity, longitude, and number of site components. This study provides the first quantitative assessment of coral communities residing at the South Texas Banks; an area that was first explored approximately 45 years ago. The unique coral assemblage is an important component to the ecology of these structures offering habitat complexity for reef associated taxa. The ecological importance of these structures as essential marine habitat is clear with having coral species of the South Texas Banks extending throughout the Gulf of Mexico suggesting connectivity within the basin occurs requiring further investigation.

Granting Institution

University of Texas Brownsville

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