17/207 Climate variability and the resilience of low diversity coral communities to bleaching in the Gilbert Islands, Kiribati Thanks to: Aranteiti Tekiau, Toaea Beiateuea, Sara E. Cannon and Simon D. Donner Tuake Teema, Salome Buglass, Matthew Department of Geography, University of British Columbia Wagstaffe, Jessica Carilli, Amy Coghlan Introduction 2009/10 El Niño Event Resilience of Disturbed Sites Coral reefs of the central equatorial Pacific have a unique Degree heating weeks reached The South Tarawa reefs, despite climate experience. The El Niño/Southern Oscillation drives up to 16°C-week in early 2010. dense human population, poor water year-to-year shifts in currents, winds, rainfall, and temperatures. Similar to a 2004/5 El Niño, quality, and flushing, feature the Sea surface temperature (SST) variability within 2-3° of the mortality was low in Tarawa highest coral cover in the region. equator is unique for the world’s coral reef regions, with SSTs and Abaiang (3-10%) despite varying more year-to-year than seasonally (Donner, 2011). high heat stress. Greater rates Porites rus (image, right), a brooder of bleaching, post-bleaching effective at recolonizing after Kiribati’s Gilbert (Tungaru) disease, and mortality were disturbance and shown to survive Islands offer a natural found in higher latitude atolls high nutrient environments, laboratory to test how (7-28% in Butaritari). dominates the reefs and has coral communities Post-bleaching disease, Butaritari expanded at some sites since 2004 respond to frequent heat Bleaching severity, measured despite the two El Niño heat stress stress. using the Bleaching Index (BI), events. 100% was not related to heat stress. 80% Out of 17 physical and Tamana, Porites rus is also common at sites TRW010 Butaritari Atoll (3°N) Tabiteuea TRW011 * Butaritari 60% experiences less El Niño-driven variability in SSTs and weather biological variables analysed, adjacent to villages with poor TRW008 MRK001 conditions than Tarawa and Abaiang (image). South Tarawa also the best predictors of BI at the Tarawa, Abaiang flushing in Butaritari and Marakei. 40% site level were light exposure, has higher nutrient and sediment loading due to a growing urban TRW002 population and shoreline modification. low CV of historical SSTs, and Iron leaching from abandoned 20% BUT001 Porites Rus (% all coral area) coralRus Poritesall(% low cover of massive and mechanical equipment and WWII 0% encrusting Porites spp. wreckage may also contribute to the 0 1 2 3 4 5 Human population metric Benthic Monitoring * Variables include maximum weekly SST, SST variability metrics, historical mean maximum SST and low diversity of South Tarawa reefs. DHW, incoming solar radiation, significant wave height, chl a concentration, and relative coral abundance Our group has worked with Kiribati’s Ministry of Fisheries and Marine Resource Development (MFMRD) since 2005 to hold Coral Community Distribution COTS vs. Heat Stress trainings and conduct regular benthic monitoring. There are distinct differences in the benthic cover and dominant A Crown-of-Thorns (COTS) starfish A set of 23 core coral taxa cover between sites with different levels of past SST outbreak (image, right) began in outer reef sites are variability and of local disturbance. From 2012 data: 2013 and spread south through assessed during Abaiang and Tarawa. It affected 100% annual/bi-annual massive taxa which had been monitoring 80% Other Bleached resilient to bleaching, especially campaigns 60% Sand/Rubble massive Porites spp. Dead coral + turf 40% conducted in Halimeda conjunction with our 20% Encrusting CA Hard coral Coral cover in Abaiang declined climate research 0% ABAIANG BUTARITARI MARAKEI S TARAWA from 25% in 2012 to 16% in 2014 (i.e., Donner and due to a COTS-driven 60% Webber, 2014). decrease in cover of massive High variability and high Porites spp. Due to winds and disturbance South Tarawa boat limitations, (TRW, red) sites are There was also a significant most sites are on Porites rus dominated, as change (p<0.01, using the leeward side shown in a PCA of 2010 Kolmogorov-Smirnov and Mann- and not all sites can quadrat data. Whitney tests, adjusted using the be sampled during Bonferroni correction) in the size each monitoring Coral cover at these sites distribution of massive Porites spp. campaign. did not decline after the from 2010 through 2014 at the 2004/5 and 2009/10 El Abaiang sites (example, right). Niño events. Methods After the 2009/10 El Niño, sites in Conclusion During each campaign, photo- and video-quadrats (20 m2 of lower disturbance North Tarawa Surveys over the past decade indicate that central equatorial Pacific reefs, images) and coral size are collected along 50 m transects and Abaiang (image, top right) subject to frequent El Niño-driven temperature variability but also cloudiness conducted at depths of 3-5 m and 10-12 m. Corals (live, dead, remained dominated by massive during El Niño events, are relatively resistant to heat stress at the individual bleached, and algae-encrusted) are identified to genus level (or Porites spp., Favia spp., (Carilli et al., 2012) and at the community level. higher). In addition: Montipora spp., Heliopora coerulea, and Halimeda algae. Bleaching resilience is highest among the most highly disturbed reefs, which • Diversity of Symbiodinium spp. in Tarawa and Abaiang corals are dominated by a species with a “weedy” life history strategy. The reefs was assessed in 2009 (Manley et al., unpub.) Sites to the north in lower feature low structural complexity and low species diversity, raising questions variability Butaritari remained • MFMRD surveyed the southern Gilberts by video in 2010 about the trade-off between resilience and conservation value. dominated by Acropora spp. after the 2009/10 event, at 20% of all • Coral cores and tissue samples were collected in 2010 to FOR MORE: benthos and 86% of coral cover in Donner SD, Kirata T, Vieux C (2010) Atoll Research Bulletin 587, 1-25 reconstruct past climate and bleaching (Carilli et al., 2012) 2012 (image, bottom right), though Donner SD (2011) Ecological Applications 21(5), 1718–1730 Carilli J, Donner SD, Hartmann A (2012) PLoS-One 7(3), e34418 • SSTs have been collected since 2012 using HOBO loggers size distribution was more positively skewed. Donner SD, Webber S (2014) Sustainability Science 9(3), 331-345 .