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Benthic Habitat Mapping
Once the project goals and data resolution needs have been determined, the physical characteristics of the study area – water clarity, depth, bottom topography , and study area size – will primarily determine what tools can effectively be used for habitat mapping. For example, if an area were known to have a rocky bottom, equipment that must penetrate the sediment for data collection (such as a sediment profile camera or a sediment corer) would not be very useful. In this case, fine-scale sampling could be conducted with video or laser line scan imaging. While there are several factors to consider when planning an effective sampling strategy, some important considerations are discussed below. Water Clarity
Tropical waters and near-shore, shallow areas that have good water clarity can be mapped using imaging techniques such as satellite imagery, aerial photography, and underwater videography. Some estuarine environments present special challenges for benthic habitat mapping, particularly those that are shallow, turbid, and consist primarily of soft and/or fine-grained sediments. In those locations, imaging techniques may not be as useful as acoustic methods. How can you map benthic habitats in turbid waters? Depth Water depth of the study area should be considered when selecting an appropriate and cost-effective system for habitat mapping. Ship-based data collection may not be feasible when surveying in water depths of less than 2 to 3 meters. Conversely, airborne methods are dependent on light reflectance, so their use is limited to water depths within the photic zone. High resolution multibeam systems can achieve 1 meter resolution in water depths of 50 meters. As water depth increases, the footprint of the sonar beams increases, which reduces the ability to discriminate small features in deeper water. Bottom Topography and Variability Once the topography and likely habitat types of the study area are determined, appropriate mapping techniques for the survey can be chosen. High-relief bottom topography and underwater geo-hazards such as rock outcrops and ledges may restrict the towing of sensors through the water in some areas.
If bottom types throughout the study area are highly variable, broad-scale characterization of the area will be more important so that the full range of habitat variability can be mapped. On the other hand, if the study area is flat or gradually sloping and contains primarily fine-grained sediments, then fine-scale sampling will be more important for defining the different habitat types. Study Area Size The geographic extent of the study area will determine whether regional surveys and / or localized sampling is required. Regional sampling techniques provide data coverage for large areas. They include satellite imaging, aircraft imaging, and acoustic surveys. Regional studies may also require the use of localized sampling to verify the broad-scale data. Localized, fine-scale techniques, such as sediment sampling, sediment profile imaging (SPI), and underwater video, or laser line scans, provide a more detailed look at smaller areas of the seafloor. If a study area is relatively small (and depending on data resolution needs), these localized sampling techniques that directly sample or observe the bottom may be sufficient to use alone. |
