Unlocking reef resilience drivers to inform Pacific coral reef management: Understanding how different nutrient sources influence coral reef resilience to thermal stress
Coral reefs are ecologically, culturally, and economically important ecosystems that are vital to the health of our planet. However, global climate change is increasing ocean temperatures, and these warmer waters are causing corals to lose their symbiotic algae that provide them with the majority of their energy, leading to coral bleaching and starvation. The 2015-2016 thermal stress event impacted reefs throughout the Pacific, with average coral mortality reaching 30%. These trends indicate an urgent need to explore all management options to increase coral survival through future bleaching events.
Palmyra, an atoll in the central Pacific, exhibited up to 90% coral bleaching in 2015-2016, but saw full recovery within two years, demonstrating Palmyra’s exceptional reef resilience. These highly resilient corals are exposed to nutrient-rich water flowing from Palmyra’s lagoon seaward. An abundant seabird population at Palmyra contribute significant pelagic nutrients to the coastal ecosystem through their guano (bird excrement), and this nutrient availability is believed to have contributed to the resilience of Palmyra’s corals. Research indicates that coral reefs near dense seabird populations have higher growth rates and are more resilient to bleaching events than similar reefs with no seabird nutrient input. The possible benefit of seabird-derived nutrients to corals is surprising because anthropogenic nutrient enrichment in coastal waters is typically associated with negative impacts to reefs. However, coral reefs appear to be responding differently to natural versus anthropogenic nutrient sources. Further exploration is needed to understand how natural nutrient inputs support reef resilience and how this contrasts with anthropogenic nutrient sources that are detrimental to reef health.
The objective of this project is to investigate the response of corals to different nutrient sources. While there has been significant research conducted on the effects of nutrient enrichment to corals, there is a gap in our understanding of how different nutrient sources (natural vs. anthropogenic) affect coral health and resilience. A secondary conservation goal of the project is to test whether this natural nutrient pathway can be simulated using other, available resources, since seabird populations are in decline and guano is not available everywhere. The plan is to test discarded fish waste from commercial fishing activities, first rendering it into a solution and then applying it to the corals, as a natural nutrient replacement for guano.
Results from this project should provide information on how guano is influencing reef resilience on remote atolls, such as Palmyra, and establish the possibility of repurposing fish waste for this novel resilience strategy. There is an urgent need to explore management actions that can support coral reefs’ persistence despite global climate change, and this project addresses knowledge gaps that could bolster reef resilience.
Marine Researcher, HIMB, UH Mānoa
Dept of Marine Biology, UH Mānoa
Palmyra Program Director, The Nature Conservancy
Hawaiʻi Sea Grant Program
NOAA Pacific Islands Regional Office
Hawaiʻi Division of Aquatic Resources