Title

Acoustic Detection of Different Types of Reef Benthos in Broward County, Florida (USA)

Event Name/Location

Ocean Sciences Meeting 2002

Document Type

Conference Proceeding

Publication Date

2002

Keywords

Data Processing, Remote Sensing, Seafloor Morphology, Seafloor Geology, Seafloor Geophysics, North America

Abstract

Benthic assemblages of variable density cover three ridges that parallel the Broward County, Florida coast at about 5-10m, 10-20m, and 20-30m depth. Two of these ridges are drowned early Holocene reefs of 5ky and 7ky uncorrected radiocarbon age respectively. In response to changes in environmental factors (hydrodynamic exposure, ambient light, etc.) the characteristics of benthic assemblages change. An acoustic bottom classification survey using QTCView 5 based on a 50 kHz transducer showed different acoustic classes on the shallow, nearshore hardground and the two deeper reeflines, which showed the same acoustic signature. Rubble beds inshore of the the third, deepest reef-line showed a mixed acoustic signature. Ground-truthing by divers utilizing traditional transect surveys showed that the differences in acoustic signature corresponded to different benthic assemblages: nearshore hardgrounds had low live cover (10%) and were dominated by algae and hydrozoa, the two deeper reef lines had the same acoustic signature and similar benthic assemblages (25-50% cover by tall sponges and gorgonians). Subtle differences in species composition existed, however since growth-form characteristics and thus acoustic surface roughness characteristics, were the same in both areas, no acoustic split was achieved. The QTCView5 was also able to differentiate between stable sands covered by a thin red algae turf and more mobile sand without turf cover. It is therefore concluded that acoustic remote-sensing methods can be used to differentiate different benthic assemblages, as long as enough differences exist in the growth-form characteristics of the dominant species to provide for a unique acoustic roughness.

Comments

Abstract #OS02-OS21F-115

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