Date of Award

2009

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Sale, Peter (Biological Sciences)

Keywords

Ecology.

Rights

CC BY-NC-ND 4.0

Abstract

Coastal defense structures currently make up more than half of the coastline in many regions, yet their ecological role is poorly understood. These structures represent novel habitat open to colonization and provide opportunity to investigate the processes driving community development in the marine environment. To investigate these processes, a series of breakwaters were studied in Dubai, UAE, where the addition of >65 km of breakwater has substantially increased the amount of hard-bottom habitat in the area. These were compared with those of natural reefs to determine whether processes structuring community development were comparable between reef types. Breakwater benthic communities appeared to follow a predictable sequence of successional development, becoming more similar to natural reefs with time. However, even the oldest breakwater community (31 yr) remained distinct from that of natural reefs. Breakwaters older than 25 yr had higher coral cover than natural reefs, but had lower diversity. Fish abundance, composition, and community structure was seasonally dynamic on >25 yr old breakwaters, resulting in divergence from natural reefs in the summer and fall, mainly as a result of adult migration and/or predation on breakwaters. Early benthic communities were comparable among tiles made of different breakwater materials. However, in areas of high coral recruitment, corals recruited preferentially to gabbro compared with concrete and sandstone. Wave exposure was an important determinant of coral community structure on breakwaters, with high post-settlement mortality resulting in a low cover coral community composed of few small colonies at sheltered sites. However, overall coral recruitment, mortality, and growth rates were comparable among leeward and windward sites and natural reefs. A manipulative caging experiment indicated few biologically significant effects from fish or urchin grazing on benthic community development. Overall, this study indicates that breakwaters can develop diverse and abundant communities, but that they are not surrogates for natural reefs.

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