Diverse coral communities in mangrove habitats suggest a novel refuge from climate change

Abstract

Abstract. Risk analyses indicate that more than 90 % of the world's reefs will be threatened by climate change and local anthropogenic impacts by the year 2030 under "business-asusual" climate scenarios. Increasing temperatures and solar radiation cause coral bleaching that has resulted in extensive coral mortality. Increasing carbon dioxide reduces seawater pH, slows coral growth, and may cause loss of reef structure. Management strategies include establishment of marine protected areas with environmental conditions that promote reef resiliency. However, few resilient reefs have been identified, and resiliency factors are poorly defined.Here we characterize the first natural, non-reef coral refuge from thermal stress and ocean acidification and identify resiliency factors for mangrove-coral habitats. We measured diurnal and seasonal variations in temperature, salinity, photosynthetically active radiation (PAR), and seawater chemistry; characterized substrate parameters; and examined water circulation patterns in mangrove communities where scleractinian corals are growing attached to and under mangrove prop roots in Hurricane Hole, St. John, US Virgin Islands. Additionally, we inventoried the coral species and quantified incidences of coral bleaching, mortality, and recovery for two major reef-building corals, Colpophyllia natans and Diploria labyrinthiformis, growing in mangroveshaded and exposed (unshaded) areas.Over 30 species of scleractinian corals were growing in association with mangroves. Corals were thriving in low-light (more than 70 % attenuation of incident PAR) from mangrove shading and at higher temperatures than nearby reef tract corals. A higher percentage of C. natans colonies were living shaded by mangroves, and no shaded colonies were bleached. Fewer D. labyrinthiformis colonies were shaded by mangroves, however more unshaded colonies were bleached. A combination of substrate and habitat heterogeneity, proximity of different habitat types, hydrographic conditions, and biological influences on seawater chemistry generate chemical conditions that buffer against ocean acidification. This previously undocumented refuge for corals provides evidence for adaptation of coastal organisms and ecosystem transition due to recent climate change. Identifying and protecting other natural, non-reef coral refuges is critical for sustaining corals and other reef species into the future.

The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

“…Understanding how these changes will co-occur and influence biological processes is one of the hardest challenges facing researchers. Natural extreme environments where multiple factors co-vary, e.g., mangrove systems (Yates et al, 2014;Camp et al, 2016a), shallow reef habitats (e.g., Price et al, 2012), macrotidal reef environments (e.g., Schoepf et al, 2015) and upwelling environments (Riegl and Piller, 2003) offer natural laboratories to address these more complex environmental questions. Notably in these systems it can be difficult to assess the relative importance of individual factors for the observed response; thus, a collective assessment with systems where one abiotic variable primarily changes is essential to advancing our understanding of how corals will survive into the future.…”

“…Mangroves are widespread reef-associated environments that have recently received attention for their potential services to corals threatened by climate change (e.g., Yates et al, 2014;Camp et al, 2016a). Mangrove systems have dynamic temperature, pH and oxygen profiles, and as such, expose resident corals to very different physicochemical conditions than neighboring reefs (Camp et al, 2017).…”

“…As such, mangrove systems appear to offer a range of potential services to corals, dependent on local spatial and temporal biogeochemical conditions. For example, work in the Caribbean (Yates et al, 2014) suggested that mangroves could act as a potential refuge for corals, through physical shading and the elevation of downstream A T as a result of carbonate-sediment dissolution (i.e., buffering potential similar to seagrass habitats), as well as frequent exposure to more variable temperatures. In other locations [e.g., the Seychelles, Indonesia (Camp et al, 2016a) and New Caledonia (Camp et al, 2017)] mangrove systems have exposed corals to simultaneously low pH, low oxygen and warmer waters relative to adjacent reefs.…”

Coral Community Structure and Recruitment in Seagrass Meadows

“…However, corals also colonize non-reef habitats, such as mangrove systems and seagrass beds that can exhibit high levels of variability in abiotic conditions relative to neighboring reefs (e.g., Riegl, 1999;Perry and Larcombe, 2003;Yates et al, 2014;Camp et al, 2016a). Despite the presence of corals in these non-reef habitats, many assessments of coral communities focus only on fore-reef zones (e.g., Mumby et al, 2007;Castillo et al, 2012).…”

A framework for assessing risk to coastal ecosystems in Taiwan due to climate change

“…Coral and algal reefs appear to be sensitive to ocean acidification and increasing temperature, but these hazards may have little or no impacts on mangroves and salt marshes. Compared to corals, mangroves are better able to resist ocean acidification because of habitat heterogeneity, proximity of different habitat types, hydrographic conditions, and biological effects on seawater chemistry generate chemical conditions that buffer against ocean acidification (Yates et al 2014). This variation in response makes comparing the risk of climate change hazards to different coastal ecosystems a major challenge and few studies focus on multiple coastal ecosystems.…”