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www.sea-technology.com August 2014 / st 25 ming at a slow, even pace, he was able to see measurement points every 10 centimeters—a much fner scale than was possible with traditional rugosity chain methods. Field Study in Bali Having realized the potential of this proof-of-concept for reef studies, Dustan and the Biosphere Foundation set out to Menjangan Island off the northwest corner of Bali, Indonesia, to study fve reef sites—four on the island and one on mainland Bali—uti- lizing the new technique. More than 125 species of reef fsh and 40 gen- era of corals have been found in the region, despite the fact that some of the reefs have been degraded by blast fshing, overfshing, anchor damage and bleaching from elevated water temperatures. "One of the degraded areas where the coral was mined to make cement was dubbed the 'Killing Fields' be- cause the distribution was near com- plete with no signs of coral recovery and/or recruitment observed on the rubble substrate," said Dustan. Other sites showed signs of intermediate damage from blast fshing, Crown-of- Thorns [starfsh] predation and/or se- vere bleaching due to climate change. "All of these disturbances highlight the need for more assiduous ecosystem- based management," he said. In general, the study sites in Bali presented a range of benthic condi- tions, which were estimated by point counting consecutive digital photos of each transect. This includes reefs with both stony and soft coral cover, those with rich undamaged coral and some with barren, rubble-like coral. In addition to widely varying amounts of coral cover, fsh popula- tions varied considerably across the different sites in terms of abundance, biomass and diversity of species. In general, the studies demonstrate that there are both physical and biological components of coral reef community structure. Tracing the Reef Prior to a frst dive, Dustan confg- ured the water level logger—an Onset (Bourne, Massachusetts) model HOBO U20-001—for deployment. Slightly larger than a cigar, the in- strument measures to a resolution of 0.41 centimeters and an accuracy of +/- 1.5 centimeters over its 30-meter depth range. Initial logger confguration involved using accompanying HOBOware soft- ware to set the sample rate and logging start time. The delayed start feature eliminated the need to bring a laptop out to the site. Based on the logger's 42,000-measurement capacity and one-second sample rate, it would be able to record continuously for a pe- riod of four to six hours before having to be downloaded, more than enough time for two or three dives during a day. At the feld site, the logger began recording on the surface to get a baro- metric pressure reading. The instru- ment was then allowed to equilibrate to seawater temperature on the sur- face, and a slow descent produced a temperature-depth profle. The logger was then rested on the reef substrate surface at the starting point of a 25-me- ter transect for a few minutes to mea- sure wave height variability. Wave height, which could have added unwanted "noise" to the data, wasn't an issue due to the gentle seas encountered in Bali, but could be a sig- nifcant factor in other areas. However, if wave height became a problem, the noise issue could have been mitigated by deploying a second stationary ref- erence logger and removing the wave variability when post-processing the data. Once the beginning of a transect was marked, which happened by rais- ing the logger, Dustan swam along info@edgetech.com USA 1.508.291.0057 Clearly Superior Imaging SONAR SYSTEMS SUB-BOTTOM PROFILERS BATHYMETRY SYSTEMS SIDE SCAN SONARS The Leader in Underwater Technology "In addition to widely varying amounts of coral cover, fsh populations varied considerably across the different sites in terms of abundance, biomass and diversity of species."