Detection of Coral Reefs and Marine Benthic Habitat Mapping Using Hydroacoustics Technology in Seribu Island Waters
Henry M. Manik, Ph.D

Source: SEAMEO BIOTROP's Research Grant | 2015


Coral reefs are valuable resources yet vulnerable. In spite of the advantages that human continue to benefit from coral reefs, the ecosystem has been subjected to serious anthropogenic threats over the past five decades or more. As most of the world's reefs are found adjacent to the coastline and majority of such areas fall in developing countries, non-sustainable activities and developments have inevitably caused rapid degradation to the ecosystem (De Silva, 1983). Activities such as blast fishing, mining of coral for building materials, and other threats like sedimentation, pollution and erection of new structures in coastal areas are diminishing the ecosystem.

With the recent global climate change, coral bleaching and mortality have become more frequent, adding to a new major threat to the well being of the world's coral reefs. Besides human induced disturbances, coral reefs are also subjected to storm damage and natural predators. Damages from natural causes are normally localized and short term. For reefs further from human reach, they have the ability to regenerate over time as there are less stress from human factor (Grigg & Dollar, 1990).

Underwater acoustic technology is a powerful tool for assessment of coral reef and observation of benthic habitat. A quantitative echo sounder was developed to estimate fish abundance rapidly and remotely for a large survey area. If we can use the quantitative echo sounder which is fisheries oriented to quantify other marine biota such as zooplankton, macrophyte, benthic organism, and sea bottom, it is very efficient because we use the same instrument both for the fish and other marine biota. From this point of view, this research was carried out to monitor and quantify marine biota by the quantitative echo sounder.

Acoustic backscattering strength of hard coral was higher than soft coral. The amplitude intensity for soft coral ranged from -35.0 to -30.0 dB, and -28.0 to -10.0 dB for hard coral. Hard coral had a higher backscatter intensity due to scattering from coarse particles, lower porosity, higher density and sound velocity, and greater roughness of the water sediment interface.

There could be many factors in combination that influence the distribution of benthic macrofauna. Two distinct feeding groups were observed from this study area: namely, deposit feeders (majority of polychaete worm sand related softbody species like nematode, oligochaetes, nemertinea, and echurids) mainly in shallow region and filter feeders (hard body bivalves and gastropods) in deeper depths.

As the conclusion, using underwater acoustics technology, we can easily and reliably quantify and qualify coral reef and its habitat.

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