For the past month, researchers aboard the NOAA Ship Hi‘ialakai have been navigating across the Pacific Ocean to survey coral reef ecosystems at remote Wake Atoll and the Mariana Archipelago. This expedition includes surveys at Jarvis Island in the Pacific Remote Islands Marine National Monument to assess the reef and degree of recovery from a catastrophic coral bleaching event in 2014–2015.
Jarvis Island is located in the central Pacific Ocean, close to the equator, and is a small island in the direct path of a deep current that flows east. Because of its position right on the equator and the strong currents hitting the island, Jarvis sits in the middle of a major upwelling zone—where cold, nutrient-rich water is drawn up from the deep. This water fertilizes the whole area, elevating nutrient levels and productivity in the reef ecosystem (Gove et al., 2006). As a result, Jarvis supports exceptionally high biomass of planktivorous and piscivorous fishes (Williams et al., 2015).
Because it is unpopulated and extremely remote, Jarvis allows us to study the natural structure, function, and variation in coral reef ecosystems. The island also offers a natural laboratory where we can assess the effects of ocean warming in the absence of local fishing and land-based sources of pollution that impact coral reefs where humans are present.
El Niño, La Niña, and the global coral bleaching event of 2014-2015
The Equatorial Pacific upwelling at Jarvis alternates between warm El Niño years, when upwelling is weak and oceanic productivity low, and cold La Niña years where upwelling is strong and productivity is high (Gove et al., 2006). Unusually warm sea surface temperatures, and a strong El Niño in 2014-2015, triggered the third recorded global coral bleaching event. At Jarvis, these warmer waters led to widespread coral bleaching and mortality. High sea surface temperatures in 2015 also impacted upwelling at Jarvis, as evidenced by a decrease in the primary productivity around the island.
Our scientists monitored coral reef ecosystems at Jarvis in April 2017. They collected data at 28 stationary point count sites.
Fish biomass tended to be highest on the western side of Jarvis, where equatorial upwelling occurs. In 2016, we observed somewhat reduced fish and planktivore biomass compared to other years, but this reduction was within the normal range of observed variability.
We observed a significant reduction of some species in 2016. These reductions were noticeable across trophic groups. For instance, the planktivorous Whitley’s fusilier (Luzonichthys whitleyi), olive anthias (Pseudanthias olivaceus), and dark-banded fusilier (Pterocaesio tile); the piscivorous island trevally (Carangoides orthogrammus), and the coral-dwelling arc-eyed hawkfish (Paracirrhites arcatus), which is strongly associated with Pocillopora coral heads. Some of these species observations returned to previous ranges by 2017, but others were still depleted.
2016 surveys showed very high levels of coral mortality, and coral cover remained low in 2017. Macroalgal cover increased in 2017, similar to the amount of coral cover lost in 2016.
Is the reduction in specific planktivore, piscivore, and live coral-dwelling fish species a widespread and long-standing shift in the fish assemblages at Jarvis? It may be due to a prolonged period of reduced food availability and changes to habitat due to the unusual warm sea conditions in 2014 and 2015. Our teams will return to Jarvis in 2018 to investigate.
Download the full monitoring brief (PDF) for additional detail on survey methods and sampling design: Jarvis Island time trends 2008-2017.
Gove J. et al. (2006) Temporal variability of current-driven upwelling at Jarvis Island. J Geo Res: Oceans 111, 1-10, doi: 10.1029/2005JC003161.
Williams I. et al. (2015) Human, oceanographic and habitat drivers of central and western Pacific coral reef fish assemblages. PLoS 10: e0120516, doi: 10.1371/journal.pone.0120516.