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A study on the recovery of Tobago's coral reefs following the 2010 mass bleaching event

University of British Columbia

The rise of ocean temperatures globally has become a grave threat to coral reefs, as it is increasing the severity and frequency of mass coral bleaching events and post-bleaching coral mortality. The continued existence of productive coral reefs will rely on corals’ ability to undergo recovery. In 2010, Tobago’s coral reefs were exposed to severe heat stress leading to mass bleaching of up to 29-60% of colonies at observed sites. This study evaluated the impact of coral bleaching and recovery of coral communities across three major reef systems in Tobago that differ in their exposure to terrestrial runoff. Assessments were done on the 1) density and composition of coral juveniles to characterise the levels of recruitment, 2) sedimentation rates and composition to understand its potential impact on recovery, and 3) species’ size frequency distributions in 2010, 2011 and 2013 to examine temporal changes among population size structure. In 2013, low juvenile densities were observed (5.41 ± 6.31 m-²) at most reef sites, which were dominated by brooding genera while broadcasting genera were rare. Sediment material, measured in May and June (end of Tobago’s dry season) was mostly terrigenous and deposited at rates below coral stress threshold levels at most sites. Out of 27 species populations assessed between all sites, 4 populations mean colony size had significantly changed by the bleaching event, and only changed 5 populations over the two following years. The few populations that were significantly altered (mainly S. siderea and M. faveolata) after the bleaching saw a rise in small sized colonies, mostl likely as a result of colony fragmentation. This study highlights that recovery via sexually produced recruits among broadcasting species was limited. While sedimentation rates were low, it is likely they are significantly higher throughout the rainy season, thus a long-term sedimentation study is highly recommended. Most coral populations resisted significant alteration from heat stress in 2010. However, given that future thermal stress is projected to become more intense, this study shows that mass bleaching disturbance could lead to decline coral population’s mean colony size, which could affect coral recovery as smaller colonies are less fecund.

Text

2015-01-06

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51752

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/