GCRMN_COI_2017-Western Indian Ocean Reef Status

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Coral reef status report for the Western Indian Ocean (2017) Global Coral Reef Monitoring Network Figure 2.1.1 Comoros archipelago’s (Grande Comore, Mohéli, and Anjouan) coral reefs and monitoring stations for which data was included in this study 2.1.3 Status and trends NATIONAL CHAPTERS Monitoring began in 1998 at 10 sites on the islands administered by the Union of the Comoros, Grande Comore, Anjouan, and Mohéli. Subsequent monitoring has targeted the same sites although data have been collected occasionally at an additional 24 sites. In 2015, reef monitoring took place at eight of the sites surveyed in 1998, with two new sites added in 2016. Across the 10 sites surveyed in 2015-2016, average coral cover was 64% on fore reefs and 40% on back reefs (fig. 2.1.2). Historical data are stored in COREMO database for surveys of live coral cover in 1999, 2002-2005, 2007, 2009, and 2011. National averages of live coral cover for each year were calculated from the available data, with between 3 and 26 sites surveyed in a year. Although there were notable declines in years with coral bleaching (2002 and 2010), coral cover increased in subsequent years and varied between 38% and 64% for fore reefs and 19% and 47% for back reefs. 54
Coral reef status report for the Western Indian Ocean (2017) Global Coral Reef Monitoring Network a b Figure 2.1.2. Trend in hard coral cover on a) all reefs in Comoros from 1998-2016 (national mean (dark blue line), 95% confidence limit (grey shaded area), individual monitoring stations (light blue lines); b) comparison by fore reef (blue line, open squares) and back reef (purple line, open circles) zones with 95% confidence limits of the mean (coloured shaded areas) Algae cover was relatively low with an average of 4% on fore reefs and 13% on back reefs in 2015-16. Fish and urchin abundance were available for only one site in 2015-16. Fish were identified and counted from a list of 30 species and were found with an abundance of 8000/ha. Urchin abundance was found to be 0.04 per m 2 . Fish abundance and biomass are available for 2011 from 2 studies. In one, 30 species in four families and sub-families were counted at 20 sites giving a mean abundance of 3200 ind/ha and biomass of 1200 kg/ha (Freed and Granek 2014). In the other, over 180 species from 17 families were counted at 8 sites, with a mean abundance of 3000 ind/ha and biomass of 400 kg/ha (M. Samoilys, unpublished data). 2.1.4 Coral bleaching 2016 During the bleaching event of 2016, bleaching was observed at several monitoring sites beginning in November 2015. Using methods compiled in the regional bleaching manual (IOC 2016) and taught to observers in 2016, an average of 21.3% bleaching of coral cover was found across seven sites in April 2016 (fig. 2.1.3). Bleaching was also observed in April at Itsoundzou on Grande Comore (estimated at 10-50%) and at Vassy and Mlongo Mhu on Anjouan (censused at 41% and 45%, respectively). Although final mortality of corals was not measured, observations in October 2016 on Anjouan indicated final mortality was less than half for bleached corals. If generalized, this observation indicates mortality of live hard corals was less than 20%. NATIONAL CHAPTERS 55
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