Award: OCE-1450214

Regime shifts are "ecological surprises" that result in a fundamental changes in the state of an ecosystem, including transitions in the abundance of species and the ecosystem services they provide. Examples include shifts from African savanna grasslands to forests or from corals to reefs dominated by macroalgae. Scientists are interested in describing these shifts, determining their causes and in predicting when and where they might occur. The 2014 – 2015 El Niño provided a unique opportunity to test the hypothesis that it would create a regime shift from corals to barnacles and to examine the overall ecological impacts of a strong climate oscillation (El Niño Southern Oscillation; ENSO) in the Galapagos rocky subtidal. More specifically, we hypothesized that extreme temperature variability from the warm El Niño to the ensuing cold La Niña would negatively impact corals as they bleach, but positively impact barnacles as they reproduce and spread during productive La Niña waters. In this scenario, barnacles settle on the stressed corals during La Niña , further contributing to the demise of corals and their eventual replacement by barnacles (regime shift). As barnacles are a vital food source for snails, fish and lobsters, a La Niña induced increase in barnacles may boost the food web. This type of positive effect on a food web is termed a bottom-up effect. As the frequency of strong ENSO's like the 2014-2015 one is projected to double with global warming, the general significance of these findings, if supported, would be that climate change does not simply create a monotonic decline in marine communities, as this ENSO driven system seems to be analogous to a roller coaster of negative and positive effects. Our temperature monitoring indicated that ecological impacts from ocean warming were likely since: 1) anomalous ocean warming typical of a strong ENSO began in May 2014 when it remained 4-5 degrees C warmer than a non- El Niño year for 4 months, 2) that 2015 temperatures were similarly elevated, and 3) that 2016 began with temperatures 3 degrees C higher than normal (Figure 1.) A delay in the onset of the El Niño - La Niña cycle during the award period prevented a complete test of the hypothesis that this ENSO would create a regime change from coral to barnacle dominance. However, the results indicated several impacts that were consistent with this scenario, such as the onset of coral bleaching in March 2016. To date, levels of coral bleaching are low with less than 5% of the coral population bleached at a given site. That is what we predicted at this point, since the subtidal system hasn't yet experienced the complete range of extreme temperature variation from the peak El Niño temperatures of March-April 2016 to the low temperatures of La Niña, which will probably occur in January- March 2017. La Niña conditions were only just declared in November 2017. We predict that a higher proportion of corals will have bleached and that the barnacle populations will have increased when we complete the next bi-annual survey during January 2017, moving the system closer to a regime shift. Analysis of our data from the previous 14 years at 12 sites supported the hypothesis of a La Niña induced bottom up effect on the food web via an increase in barnacles. For example, there were significant positive correlations between barnacle abundance from 2002-2014 and the El Niño Southern Oscillation Index at 5 sites. Furthermore, the abundance of fish known to feed on barnacles in 2015 was positively correlated to the abundance of barnacles in 2012 and 2013. All this information was transmitted to the Galapagos National Park Directorate in oral presentations and in written reports as it will help them manage the Galapagos Marine Reserve in an era of climate change. Funding from this award sponsored training in field marine ecology and conservation for one post-doctoral researcher (Dr. Franz Smith), one PhD (Robert Lamb), one undergraduate student (Fiona Beltram) and a part -time technician (Eliza Moore) at Brown University. Information from this research program has been communicated to the public in 4 talks at Benthic Ecology meetings and in 2 talks at the 13th International Coral Reef Symposium. Some of the results were also incorporated into the Principal Investigator's lectures in the Ecology course at Brown University. Last Modified: 12/30/2016 Submitted by: Jon D Witman Subtidal temperature data documenting the onset and persistence of the 2015-2016 El Nino conditions at 12 research sites in the Galapagos Islands are available at https://www.bco-dmo.org/dataset/628180 Temperatures were sampled at 10 minute intervals from July 2015 to January 2016. These data complement earlier temperature data posted from 2014 at http://www.bco-dmo.org/project/620072. A dataset on the percent cover of barnacles, Megabalanus sp. at 10-12 of the Galapagos subtidal research sites (in January 2015, January 2016) is also posted on this same project website. The abundance of barnacles is an ecological response to La Nina conditions. Last Modified: 02/16/2017 Submitted by: Jon D Witman