What Happened to Jarvis Island's Reef Fish After the 2014–2015 Coral Bleaching

In April 2017, scientists aboard the NOAA Ship Hi'ialakai, on a voyage to survey the reefs of Wake Atoll and the Mariana Archipelago, stopped at Jarvis Island to see how its reef was recovering from the catastrophic coral bleaching of 2014–2015.

One of the few table Acropora corals left at Jarvis Island in April 2017; the rest of the reef is carpeted in red turf algae growing over dead coral. NOAA Fisheries.

A natural laboratory

Jarvis is a small, uninhabited island in the Pacific Islands Heritage Marine National Monument, right on the equator and in the path of a deep eastward current. Where the current strikes the island, cold, nutrient-rich water wells up from the depths and fertilizes the reef, which supports an exceptional mass of fish that eat plankton and fish that eat other fish. With no people, no fishing and no pollution from land, it is a natural laboratory for seeing what ocean warming alone does to a reef.

Sea surface temperatures around Jarvis Island and the Pacific Remote Islands. NOAA Fisheries.

Seafloor depths around Jarvis Island. NOAA Fisheries.

El Niño and the bleaching

The upwelling swings with the climate: weak in warm El Niño years, when the ocean around the island is less productive, and strong in cold La Niña years. Unusually warm seas and a strong El Niño in 2014–2015 triggered the third recorded global coral bleaching event. At Jarvis the warm water bleached and killed coral across the reef, and in 2015 it also weakened the upwelling, cutting the ocean's productivity around the island.

What the 2017 survey found

The team counted fish and recorded the seafloor at 28 sites, using the stationary point count method. Fish were most abundant on the western side, where the upwelling is.

• Overall fish biomass dipped somewhat in 2016 but stayed within the normal range from year to year.
• Particular species fell sharply in 2016, across feeding groups: plankton-eaters such as Whitley's fusilier, the olive anthias and the dark-banded fusilier; the island trevally, which eats fish; and the arc-eyed hawkfish, which lives among Pocillopora corals. Some had recovered by 2017; others had not.
• A newcomer. Several common fusiliers were seen less often in 2017, but the wide-band fusilier, never recorded at Jarvis before, turned up.
• The coral did not come back. Coral mortality in 2016 was very high and cover stayed low in 2017, while macroalgae spread over roughly as much reef as the coral had lost.

The wide-band fusilier, first recorded at Jarvis in 2017. NOAA Fisheries.

Fish biomass at survey sites around Jarvis Island, 2008 to 2017. NOAA Fisheries.

Average biomass of selected species in each survey year. NOAA Fisheries.

Cover of hard coral (top), macroalgae (middle) and crustose coralline algae (bottom) by survey year; there are no estimates for 2008. NOAA Fisheries.

A lasting shift?

Are the losses of particular plankton-eaters, fish-eaters and coral-dwellers a lasting change in Jarvis's fish community? They may reflect a long stretch of scarce food and changed habitat after the warm seas of 2014 and 2015. One sign of hard times was an emaciated grey reef shark seen during the 2017 survey. The team planned to return in 2018 to find out more.

An emaciated grey reef shark seen during a 2017 fish survey. NOAA Fisheries.

Sources

• NOAA Fisheries, "What Happens to Reef Fish After Coral Bleaching?"; rewritten in hubnx's own words. Photographs and figures: NOAA Fisheries.
• NOAA Fisheries, Jarvis Island time trends 2008–2017, the monitoring brief.