Abstract
Seagrass meadows, one of the most important habitats for many marine species, provide essential ecological services. Thus, society must conserve seagrass beds as part of their sustainable development efforts. Conserving these ecosystems requires information on seagrass distribution and relative abundance, and an efficient, accurate monitoring system. Although narrow multibeam sonar systems (NMBSs) are highly effective in resolving seagrass beds, post-processing methods are required to extract key data. The purpose of this study was to develop a simple method capable of detecting seagrass meadows and estimating their relative abundance in real time using an NMBS. Because most seagrass meadows grow on sandy seafloors, we proposed a way of discriminating seagrass meadows from the sand bed. We classify meadows into three categories of relative seagrass abundance using the 95% confidence level of beam depths and the depth range of the beam depth. These are respectively two times the standard deviation of beam depths, and the difference between the shallowest and the deepest depths in a 0.5 × 0.5 m grid cell sampled with several narrow beams. We examined Zostera caulescens Miki, but this simple NMBS method of seagrass classification can potentially be used to map seagrass meadows with longer shoots of other species, such as Posidonia, as both have gas filled cavities.
Highlights
Seagrass are submersed marine angiosperms that grow mainly on sandy or muddy substrates in shallow coastal and estuarine waters, forming meadows to provide habitat and shelter for many marine organisms [1,2,3]
The beam depths data obtained from the narrow multibeam sonar systems (NMBSs) could draw but only those from the sand bed at Stn. 10
The beam depths data obtained from the NMBS could above-ground parts of seagrass the sand at Stn.bed
Summary
Seagrass are submersed marine angiosperms that grow mainly on sandy or muddy substrates in shallow coastal and estuarine waters, forming meadows to provide habitat and shelter for many marine organisms [1,2,3]. Seagrass meadows are estimated to cover less than 0.2 percent of the global ocean [4], seagrass supports different trophic levels of marine species [5] and are known to be important in spawning, and larval and juvenile stages of many commercially important fish, mollusks and crustaceans [6,7] They contribute to the marine environment in several ways, fixing carbon via photosynthesis [8], stabilizing bottom sediments with their root systems, and maintaining coastal water quality and clarity through nutrient uptake [9,10,11,12].
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