It is important to be aware of such limitations, the situations in which they are
most likely to occur, and the extent of our ability to correct associated errors.
Given that each acoustic mapping tool has different strengths and weaknesses,
integrated surveys combining multiple acoustic mapping tools along with georeferenced environmental parameters and ‘ground-truth’ data represent an optimal
approach for studying cold-water coral ecosystems. This chapter describes a survey approach using both an autonomous underwater vehicle (AUV) and submersible dives. The AUV acquires geo-referenced parameters (i.e., bathymetry,
backscatter, current regime data, sub-bottom profiles, and measurements of
chemical-physical water properties) that are unprecedented in quality and resolution. These parameters are then ground-truthed via submersible video transects
and bottom samples. Two case studies from the Straits of Florida are described
here as examples of quantitative analyses that can be performed with such datasets,
and to illustrate the level of resolution (e.g., sub-meter or decameter scales)
necessary for studying cold-water coral ecosystems.
10.2 History of Mapping Cold-Water Coral Habitats
Samples of cold-water coral species have been retrieved from the seafloor via
dredging for over a century (Pourtales 1868; Cairns 1979). However, it was not
until the 1960s that single-beam echosounding surveys revealed that cold-water
corals form high relief mounds, similar to the reefs generated by shallow water
corals in the tropics and sub-tropics (Teichert 1958; Stetson et al. 1962). Following
this discovery, submersible dives were used to investigate the distribution of coldwater corals and associated fauna across mounds (Neumann and Ball 1970;
Neumann et al. 1977; Reed 1980; Messing et al. 1990). Hypotheses regarding
mound morphology and its relation to the local bottom current were important
outcomes of these surveys. The Neumann et al. (1977) description of streamlined
mounds aligned parallel to the northward flowing Florida Current on the Bahama
Bank slope became a model for deep-water mounds, and strongly influenced
subsequent studies in the field. Despite this progress in characterizing cold-water
coral fields, the precise locations of coral mounds, their sizes, and abundances
remained poorly understood due to the limited spatial coverage of early surveys.
Concurrent advances in the application of industrial seismic data to deep-water
environments revealed additional sites covered by cold-water coral mounds, and
also stimulated new hypotheses regarding the processes controlling mound distribution and development (e.g., Hovland et al. 1994; Del Mol et al. 2002). In some
areas, tectonic faults were identified and mapped beneath mound structures. These
faults were interpreted to be conduits of hydrocarbons (mainly methane) that serve
as a food basis for cold-water corals and associated fauna (Hovland et al. 1990,
1994). High-resolution seismic data often showed that mounds were rooted on
truncated reflectors formed during erosive events, indicating that bottom current
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most likely to occur, and the extent of our ability to correct associated errors.
Given that each acoustic mapping tool has different strengths and weaknesses,
integrated surveys combining multiple acoustic mapping tools along with georeferenced environmental parameters and ‘ground-truth’ data represent an optimal
approach for studying cold-water coral ecosystems. This chapter describes a survey approach using both an autonomous underwater vehicle (AUV) and submersible dives. The AUV acquires geo-referenced parameters (i.e., bathymetry,
backscatter, current regime data, sub-bottom profiles, and measurements of
chemical-physical water properties) that are unprecedented in quality and resolution. These parameters are then ground-truthed via submersible video transects
and bottom samples. Two case studies from the Straits of Florida are described
here as examples of quantitative analyses that can be performed with such datasets,
and to illustrate the level of resolution (e.g., sub-meter or decameter scales)
necessary for studying cold-water coral ecosystems.
10.2 History of Mapping Cold-Water Coral Habitats
Samples of cold-water coral species have been retrieved from the seafloor via
dredging for over a century (Pourtales 1868; Cairns 1979). However, it was not
until the 1960s that single-beam echosounding surveys revealed that cold-water
corals form high relief mounds, similar to the reefs generated by shallow water
corals in the tropics and sub-tropics (Teichert 1958; Stetson et al. 1962). Following
this discovery, submersible dives were used to investigate the distribution of coldwater corals and associated fauna across mounds (Neumann and Ball 1970;
Neumann et al. 1977; Reed 1980; Messing et al. 1990). Hypotheses regarding
mound morphology and its relation to the local bottom current were important
outcomes of these surveys. The Neumann et al. (1977) description of streamlined
mounds aligned parallel to the northward flowing Florida Current on the Bahama
Bank slope became a model for deep-water mounds, and strongly influenced
subsequent studies in the field. Despite this progress in characterizing cold-water
coral fields, the precise locations of coral mounds, their sizes, and abundances
remained poorly understood due to the limited spatial coverage of early surveys.
Concurrent advances in the application of industrial seismic data to deep-water
environments revealed additional sites covered by cold-water coral mounds, and
also stimulated new hypotheses regarding the processes controlling mound distribution and development (e.g., Hovland et al. 1994; Del Mol et al. 2002). In some
areas, tectonic faults were identified and mapped beneath mound structures. These
faults were interpreted to be conduits of hydrocarbons (mainly methane) that serve
as a food basis for cold-water corals and associated fauna (Hovland et al. 1990,
1994). High-resolution seismic data often showed that mounds were rooted on
truncated reflectors formed during erosive events, indicating that bottom current
256
T. B. S. Correa et al.