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Brown C, Browne N, McIlwain JL, Zinke J.2018. Inshore, turbid coral reefs from northwest Borneo exhibiting low diversity, but high cover show evidence of resilience to various environmental stressors. PeerJ Preprints6:e27422v1https://doi.org/10.7287/peerj.preprints.27422v1
For reefs in SE Asia the synergistic effects of rapid land-development, insufficient environmental policies and a lack of enforcement has led to poor water quality and compromised coral health from increased sediment and pollution. Those inshore turbid coral reefs, subject to significant sediment inputs, may also inherit some resilience to the effects of thermal stress and coral bleaching. We studied the inshore turbid reefs near Miri, in northwest Borneo, through a comprehensive assessment of coral cover, health and function in addition to quantifying sediment-related parameters. Although Miri Reefs had comparatively low coral species diversity, dominated by massive and encrusting forms of Diploastrea, Porites, Montipora, Favites, Dipsastrea and Pachyseris, they were characterised by a healthy cover ranging from 22-39%. We found a strong inshore to offshore gradient in hard coral cover, diversity and community composition as a direct result of spatial differences in sediment but over scales of <10 km. As well as distance to shore, we included other environmental variables like reef depth and sediment accumulation/size that explained 62.5% of variation in benthic composition among sites. None of the reefs showed evidence of coral disease and relatively low prevalence of compromised health signs including bleaching (6.7%), bioerosion (6.6%), pigmentation (2.2%), scars (1.1%) and mucus production (0.5%). There were, however, seasonal differences in bioerosion rates which increased five-fold after the 2017 wet season. Tagged colonies of Diploastrea and Pachyseries showing partial bleaching in 2016, had fully recovered by 90-100% the following year. Differences in measures of coral function like that of symbiont density and chlorophyll a for Montipora, Pachyseris and Acropora were not detected among sites. This study provides further evidence that turbid coral reefs exposed to seasonally elevated sediment loads can exhibit relatively high coral cover and be resilient to disease and elevated sea surface temperatures.
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Photographs of the 5 stages of symbiont cell degradation. A. Symbiont cells on the haemocytometer, B. stage 1, C. stage 2, D. stage 3, E. stage 4, and F. stage 5
Average density for A. symbiont and B. chlorophyll a pigment for three coral species (Acropora, Montipora, Pachyseris) sampled in May 2017 at the three surveyed sites (EG = Eve’s Garden, AG = Anenome’s Garden, Siwa)
DbRDA plots based on the DistLM with AIC model selection with the three significant (p<0.05) drivers of coral health for A. scars, B. pigmentation, C. bioerosion, and D. bleaching. The bubble sizes represent prevalence percentages with each bubble represe
DbRDA plots based on the DistLM with AIC model selection with all the sediment drivers for A. scars, B. pigmentation, C. bioerosion, and D. bleaching. Note that only course and fines are significantly (p<0.05) explaining 18% of the variation in coral heal