Project: Documenting bleaching susceptibility and resilience in Guam, Micronesia

Note: This project is funded by an NSF RAPID award.

Description from NSF award abstract:
Coral reef ecosystems are experiencing unprecedented levels of environmental stress. Guam, Micronesia is currently experiencing an island-wide coral bleaching event unprecedented in recent decades. The available evidence suggests that the severity and extent of this event is linked to extended high sea surface temperature and a delay in the onset of the rainy season. Initial surveys of coral reefs around the island indicate that the impacts are broad in both geographic extent and the number of coral species affected. This project will support a quantitative examination of the patterns of mortality and recovery of corals from this event in the context of reef resilience, or their ability to recover. Specifically, the project will examine whether: (a) exposure differences between the east and west sides of the island result in differential recovery, and (b) do sites that showed lower bleaching severity during initial surveys show higher recovery post-bleaching? It is predicted that differential bleaching is due, in part, to genetic differences in both the coral host and its symbiotic algae and identifying unique host-symbiont combinations that are less sensitive to extreme temperature anomalies will be a primary goal of this project. These hypotheses and predictions will be addressed by returning to a select subset of reef sites over time by a rapid response team using survey methods as employed at the NSF funded Moorea Coral Reef Long Term Ecological Research (LTER) site which includes permanent transects and fixed quadrats, and computer software to document changes in the percent cover of corals over time. Additionally, long-term monitoring of tagged colonies in the genera Acropora and Pocillopora, specifically for their recovery, and for detailed genetic analyses to examine host and symbiont genetic diversity, will help determine which combinations of host-symbiont genotypes are exhibiting recovery versus mortality.

The proposed work will reveal which specific sites, environmental conditions, and genotypes are associated with resilience to coral bleaching and will allow establishment of a system whereby long-term recovery can be documented and also compared to the Moorea LTER data on coral reef resilience. Such data sets are rare or non-existent in Micronesia and the ability to identify resilient populations can provide information to help prioritize management efforts and evaluate the performance of existing marine parks and preserves.

Further description from PI:

Survey Methods: The investigators will address these hypotheses and predictions by returning to a select subset of sites visited by the rapid response team and using survey methods as employed at the Moorea Coral Reef LTER (i.e., http://mcr.lternet.edu). On each coast, the investigators will select reef sites that have shown high (n=2) and low (n=2) levels of bleaching for a total of 8 sites. At each of the sites, they will establish permanent transacts (five 10 m transects) with fixed quadrat (0.25 m2) locations (n=40 total) for quarterly photomonitoring (see Edmunds 2013). The investigators will also deploy temperature loggers along the transects for the duration of the proposed study. Photographed quadrats will be analyzed using CPCe software as described in Adam et al (2011) to document changes in benthic cover.

To examine individual colony responses more closely, a subset of colonies from specific genera will be tagged at each site and re-assessed periodically for one year. At present, the investigators are considering Acropora spp and Pocillopora spp, as these are ecologically important, highly impacted by this event, and common to many of the sites being surveyed at present. The tagged colonies will be identified to species, and their health status documented: i.e.,  bleached, fully pigmented, re-sheeting, partial mortality, full mortality. The investigators will also look for signs of disease at the same time.

Genetic Analyses: The species selected above will be sampled for genetic analysis, to identify zooxanthellae clades present in each colony (see Gates 2011), examine host genetic diversity (e.g., Combosch & Voller 2011), and determine which combinations of host-symbiont genotypes are exhibiting recovery vs. mortality. As the event is coming to a close, and the investigators are already seeing mortality in certain species, they may be unable to sample certain highly susceptible colonies, but they will work under the assumption that surviving colonies represent the most resilient host-symbiont genotypes and certain colonies with partial mortality will allow sampling of remaining tissue.

The investigators will determine if there are associations between resilient genotypes and site-specific environmental conditions, obtaining secondary data on sea surface temperatures along the east vs. west coasts, rainfall, and wave height from NOAA and the National Weather Service. They will also document degree of exposure and distance to point sources of terrestrial inputs at each site.

Bibliography
Adam, T.C., Schmitt, R.J., Holbrook, S.J., Brooks, A.J., Edmunds, P.J., Carpenter, R.C., Bernardi, G., 2011. Herbivory, Connectivity, and Ecosystem Resilience: Response of a Coral Reef to a Large-Scale Perturbation. Plos One 6. DOI: 10.1371/journal.pone.0023717

Combosch, D.J., Vollmer, S.V., 2011. Population Genetics of an Ecosystem-Defining Reef Coral Pocillopora damicornis in the Tropical Eastern Pacific. Plos One 6. DOI: 10.1371/journal.pone.0021200

Edmunds, P of Moorea Coral Reef LTER. 2013. MCR LTER: Coral Reef: Long-term Population and Community Dynamics: Corals. knb-lter-mcr.4.29 (http://metacat.lternet.edu/knb/metacat/knb-lter-mcr.4.29/lter).

Gates, R of Moorea Coral Reef LTER. 2011. MCR LTER: Coral Reef: Population Dynamics: Time-series of Symbiodinium populations in corals of Moorea. knb-lter-mcr.15.11 (http://metacat.lternet.edu/knb/metacat/knb-lter-mcr.15.11/lter).