What happens to reef fish after coral bleaching?

by Adel Heenan

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 additional surveys at Jarvis Island, in the Pacific Remote Islands Marine National Monument, to assess the reef condition 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 (Figure 1). Because of it’s 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 provides an important reference point and opportunity to understand the natural structure, function, and variation in coral reef ecosystems. The island also offers a natural laboratory in which the effects of ocean warming can be assessed in the absence of stressors that impact coral reefs where humans are present (e.g., fishing or land-based sources of pollution).

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.

Teams from the Coral Reef Ecosystem Program recently completed ecological monitoring at Jarvis from April 2–5, 2017. They collected data at 28 stationary point count sites (Figure 2) this year, 30 in 2016, 62 in 2015, 42 in 2012, and 30 in 2010.


Figure 2. The stationary point count method is used to monitor the fish assemblage and benthic communities at the Rapid Ecological Assessment (REA) sites.

Main Observations
Fish biomass tended to be highest on the western side of the island where equatorial upwelling occurs (Figure 3). In 2016, we observed somewhat reduced total fish and total planktivore biomass (Figure 4), but this reduction was within the normal range of observed variability.

There were some significant reductions observed for individual species in 2016. These reductions were noticeable across multiple trophic groups, for instance the planktivorous Whitley’s fusilier (Luzonichthys whitleyi), Olive anthias (Pseudanthias olivaceus), 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 had returned to previous ranges by 2017, but others remain depleted (Figure 5).


Figure 5. Mean species biomass (± standard error) per survey year at Jarvis.

Very high levels of coral mortality were evident in 2016 surveys and coral cover remained low in 2017. Notably, macroalgal cover increased in 2017, approximately by the amount of coral cover lost in 2016 (Figure 6).


Figure 6. Mean percentage cover estimates (± standard error) of benthic habitat per survey year at Jarvis. Data shown for Hard Coral (top, red); macrolagae (middle, green) and CCA: crustose coralline algae (bottom, orange). Note: no benthic data are available for 2008 as we began collected rapid visual estimates of these benthic functional groups in 2010.

Whether this reduction in specific planktivore, piscivore, and live coral-dwelling fish species is a widespread and long-standing shift in the fish assemblages at Jarvis will be the subject of forthcoming research. It seems plausible that they reflect impacts of a prolonged period of reduced food availability and changes to preferred habitat due to the anomalous warm sea conditions in 2014–2015. Our teams will return to Jarvis in 2018 to conduct another assessment in an attempt to answer some of these questions.


An emaciated grey reef shark (Carcharhinus amblyrhynchus) observed during a 2017 fish survey. (Photo: NOAA Fisheries/Adel Heenan)

Additional detail on survey methods and sampling design are available in the full monitoring brief: 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.


Assessing impacts of coral bleaching: NOAA scientists embark on a three-month survey of coral reef ecosystems in the Hawaiian Archipelago

by Drs. Bernardo Vargas-Ángel and Rusty Brainard

French Frigate Shoals in the Northwestern Hawaiian Islands (NOAA Photo)

Today, scientists from the NOAA Pacific Islands Fisheries Science Center’s Coral Reef Ecosystem Program boarded the NOAA Ship Hi‘ialakai to begin a 75-day Hawaiian Archipelago Reef Assessment and Monitoring Program (HARAMP) research mission. The goal of this mission is to document the status and trends of the coral reef ecosystems of the populated main Hawaiian Islands and the remote Papahānaumokuākea Marine National Monument in the uninhabited Northwestern Hawaiian Islands.

As part of the National Coral Reef Monitoring Program of NOAA’s Coral Reef Conservation Program, this HARAMP expedition will conduct the first statewide surveys to assess the overall impacts of two back-to-back mass coral bleaching events, which occurred in 2014 and 2015 and were caused by unusually warm water temperatures. When water temperatures reach 1°C warmer than their usual summertime maximum, many corals begin to lose the symbiotic algae living in their tissues, making them look white — that is, they become “bleached.”

This expedition will be the 6th monitoring cruise in the main Hawaiian Islands and the 10th monitoring cruise in the Northwestern Hawaiian Islands led by the PIFSC Coral Reef Ecosystem Program and partner agencies since 2000. It’s designed to provide an ongoing, consistent flow of information to document the status and long-term trends of the coral reefs and changing environmental conditions.

These statewide monitoring surveys will complement the local and site-specific coral reef monitoring efforts led by our partner agencies and institutions. Partners participating in this mission include scientists from the State of Hawai‘i Division of Aquatic ResourcesThe Nature ConservancyHawai‘i Institute of Marine Biology, and San Diego State University, among others.


Autonomous Reef Monitoring Structure installed on left, calcification accretion unit on right (NOAA Photo)

Scientists will survey the coral reefs around each of the main Hawaiian Islands, including Ni‘ihau, Kaua‘i, O‘ahu, Molokai, Lāna‘i, Maui, Kaho‘olawe, and Hawai‘i Islands, and the coral reefs at French Frigate Shoals, Lisianski/Neva Shoals, Pearl and Hermes Atoll, and Kure Atoll in the Northwestern Hawaiian Islands. Each day, they will deploy 4–5 small boats with a team of scientific divers from the Hi`ialakai to conduct in-water surveys of the different reef zones, such as forereef, backreef, and lagoons around the different sides of each island or atoll ecosystem. We often find that the coral reefs and associated organisms vary greatly between leeward and windward sides of islands that are exposed to different environmental conditions, such as waves and currents.

Coral Reef

Under the direction of Chief Scientists Drs. Bernardo Vargas-Ángel in the main Hawaiian Islands and Brett Schumacher in the Northwestern Hawaiian Islands, the different dive teams will conduct underwater surveys of reef fishes, corals, other invertebrates, algae, and microbes. They will deploy and retrieve Autonomous Reef Monitoring Structures, or ARMS, to assess the biodiversity of ‘cryptic’ coral reef species that live within the reef (small crabs, shrimp, snails, etc.).

Autonomous Reef Monitoring Structures (ARMS) installed at Pearl and Hermes Atoll, NWHI (NOAA Photo)

Autonomous Reef Monitoring Structures (ARMS) installed at Pearl and Hermes Atoll, NWHI (NOAA Photo)

Close-up of ARMS unit at Pearl and Hermes Atoll, NWHI (NOAA Photo)

Close-up of ARMS unit at Pearl and Hermes Atoll, NWHI (NOAA Photo)

Calcification accretion unit installed at French Frigate Shoals, NWHI (NOAA Photo)

Calcification accretion unit installed at French Frigate Shoals, NWHI (NOAA Photo)







Additionally, oceanographers aboard the Hi`ialakai will collect data on water temperature, salinity, carbonate chemistry, and other physical characteristics of the coral reef environment with an assortment of oceanographic monitoring instruments. Among other things, they’re monitoring the ecological impacts of ocean acidification by determining the rates of reef growth and reef removal using tools called calcification accretion units and bioerosion monitoring units, respectively, which are deployed on the reef substrate for three years.

Data collected by the scientific staff of this cruise are pivotal to long-term biological and oceanographic monitoring of coral reef ecosystems in the Hawaiian Archipelago. This 2016 HARAMP expedition will help inform scientists, resource managers, and policy makers about changes that have occurred compared with similar surveys conducted in 2000, 2001, 2002, 2003, 2004, 2005 (main Hawaiian Islands only), 2006, 2008, 2010, and 2013.

Hawaiian Archipelago Reef Assessment and Monitoring Program Cruise 2016 Timeline

In particular, data on the abundance and spatial distribution of reef fishes and benthic organisms will allow scientists to evaluate potential changes in the condition and integrity of coral reef ecosystems across the Hawaiian Archipelago. It will also enable federal and state resource managers to more effectively manage and conserve reef-associated animal and plant life in the region. This year’s surveys are particularly important since many of the coral reefs experienced mass coral bleaching in both 2014 and 2015, and these surveys will provide an opportunity to assess the net change in coral cover for each of the islands across the archipelago.


Coral reef monitoring surveys completed around the islands and atolls of American Samoa

By Bernardo Vargas-Ángel
Operating area of the HA-15-01 ASRAMP Legs II and III.

Operating area of the HA-15-01 ASRAMP Legs II and III.

With work complete in the U.S. territory of American Samoa, the NOAA Ship Hi‘ialakai stopped in the port of Pago Pago Harbor for a short pause between Legs III and IV of PIFSC cruise HA-15-01. Led by the PIFSC Coral Reef Ecosystem Division (CRED), this mission marks the seventh monitoring cruise in the American Samoa region by PIFSC staff and partner agencies since 2002.

Activities to monitor the coral reef ecosystems of American Samoa began on February 17 and concluded on March 30, completing Leg I and comprising Legs II and III of this longer Pacific Reef Assessment and Monitoring Program (Pacific RAMP) expedition. Around Tutuila, Aunu‘u, Ofu-Olosega, Swains, and Ta‘u Islands, and Rose Atoll, the CRED scientists conducted ecosystem surveys of fishes, benthic and coral communities, and microbes, along with the deployment of oceanographic instruments and biological installations.

Shallow coral reef communities at Rose Atoll, conspicuously dominated by the pink-colored encrusting coralline algae.

Shallow coral reef communities at Rose Atoll, conspicuously dominated by the pink-colored encrusting coralline algae.

A pair of the reticulated butterflyfish (Chaetodon reticulatus) at Swains Island.

A pair of the reticulated butterflyfish (Chaetodon reticulatus) at Swains Island.

At Rapid Ecological Assessment (REA) sites, surveys for reef fishes and benthic coral communities documented the richness, abundance, density, and sizes of the biota and assemblages as well as the percent composition of bottom-dwelling organisms and the health conditions of coral colonies. Broad-scale towed-diver surveys recorded observational data on large-bodied fishes (>50 cm total length), percent composition of the seafloor, conspicuous macroinvertebrates, and coral stress.

In addition, teams studied microbial communities, diversity of cryptic invertebrates, water temperature, salinity, and carbonate chemistry. They are also working to assess the potential early effects of ocean acidification on cryptobiota (e.g. small, hidden organisms) and the rates of reef carbonate deposition, bioerosion, and coral calcification.

Across the Territory of American Samoa, this mission completed more than 60 towed-diver surveys totaling more than 130 km of coastline, 325 fish surveys, and 180 benthic surveys. The Ocean and Climate Change team deployed four climate monitoring stations around Tutuila, and four around Ofu-Olosega and Ta‘u, containing arrays of subsurface temperature recorders (STRs), calcification accretion units (CAUs), autonomous reef monitoring structures (ARMS), and bioersion monitoring units (BMUs). Critical findings during this mission included observations of coral bleaching, local warm water temperatures, and the number and distribution of corallivore crown-of-thorns sea stars (COTS).

Bleached and partly dead staghorn Acropora outside Fagatele Bay, Tutuila, American Samoa.

Bleached and partly dead staghorn Acropora outside Fagatele Bay, Tutuila, American Samoa.

Bleaching of scleractinian corals, averaging 10% of colonies, was reported in shallow (3-6 m) reef habitats of Tutuila Island—particularly within Fagatele and Fagasa Bays—as well as the southwest coast of the island and primarily affected species of branching and table Acropora, Isopora, Montastrea, Porties, and Pocillopora. Although bleaching conditions did not appear to be widespread, current NOAA Coral Reef Watch forecasts predict persistent warm conditions, which could potentially result in more severe and extensive coral bleaching across the region. CRED scientists recorded only occasional sightings of COTS and their feeding scars on corals, despite the ongoing outbreak conditions reported by staff of the National Park Service and the National Marine Sanctuary of American Samoa. In contrast to other regions where COTS outbreaks have been reported by CRED scientists, including Guam, the Commonwealth of the Northern Mariana Islands, and Kingman Reef, it appears that in American Samoa, the sea stars prefer to feed at night and hide under ledges and overhangs during the day, making them inconspicuous during daylight surveys.

Preliminary results from surveys conducted by CRED fish team divers, during PIFSC cruise HA-15-01, are provided in the fish monitoring brief below.

Pacific Reef Assessment and Monitoring Program
Fish monitoring brief: American Samoa 2015

By Adel Heenan

About this summary brief
The purpose of this summary brief is to outline the most recent survey efforts conducted by the Coral Reef Ecosystem Division (CRED) of the NOAA Pacific Islands Fisheries Science Center as part of the long-term Pacific Reef Assessment and Monitoring Program (Pacific RAMP). More detailed survey results will be available in a forthcoming status report.

Sampling effort

  • Ecological monitoring took place in American Samoa from February 15 2015 to March 30 2015.
  • Data were collected at 338 sites. Surveys were conducted at Ofu and Olosega (n=52), Rose (n=47), Swains (n=32), Tau (n=46) and Tutuila (n=162).
  • At each site, the fish assemblage was surveyed by underwater visual census and the benthic community was assessed.

Overview of data collected
Primary consumers include herbivores (which eat plants) and detritivores (which bottom feed on detritus), and secondary consumers are largely omnivores (which mostly eat a variety of fishes and invertebrates) and invertivores (which eat invertebrates).

Figure 1. Mean total fish biomass at sites surveyed.

Figure 1. Mean total fish biomass at sites surveyed.

Figure 2. Mean hard coral cover at sites surveyed.

Figure 2. Mean hard coral cover at sites surveyed.

Spatial sample design
Survey site locations are randomly selected using a depth-stratified design. During cruise planning and the cruise itself, logistic and weather conditions factor into the allocation of monitoring effort around sectors of each island or atoll. The geographic coordinates of sample sites are then randomly drawn from a map of the area of target habitat per study area. The target habitat is hard-bottom reef, the study area is typically an island or atoll, or in the case of larger islands, sectors per island, and the depth strata are shallow (0-6 m), mid (6-18 m), and deep (18-30 m).

Sampling methods
A pair of divers surveys the fish assemblage at each site using a stationary-point-count method. Each diver identifies, enumerates, and estimates the total length of fishes within a visually estimated 15-m-diameter cylinder with the diver stationed in the center. These data are used to calculate fish biomass per unit area (g m-2) for each species. Mean biomass estimates per island are calculated by weighting averages by the area per strata. Island-scale estimates presented here represent only the areas surveyed during this cruise. For gaps or areas not surveyed during this cruise, data from this and other survey efforts will generally be pooled to improve island-scale estimates.

Figure 3. Mean consumer group fish biomass (± standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 3. Mean consumer group fish biomass (± standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 4. Mean fish biomass per size class (± standard error). Fish measured by total length (TL) in centimeters (cm).

Figure 4. Mean fish biomass per size class (± standard error). Fish measured by total length (TL) in centimeters (cm).

Each diver also conducts a rapid visual assessment of reef composition, by estimating the percentage cover of major benthic functional groups (encrusting algae, macroalgae, hard corals, turf algae and soft corals) in each cylinder. Divers also estimate the complexity of the surface of the reef structure, and they take photos along a transect at each site that are archived to allow for future analysis.

About the monitoring program
Pacific RAMP forms a key part of the National Coral Reef Monitoring Plan of NOAA’s Coral Reef Conservation Program (CRCP), providing integrated, consistent, and comparable data across U.S. Pacific islands and atolls. CRCP monitoring efforts have these aims:

  • Document the status of reef species of ecological and economic importance
  • Track and assess changes in reef communities in response to environmental stressors or human activities
  • Evaluate the effectiveness of specific management strategies and identify actions for future and adaptive responses

In addition to the fish community surveys outlined here, Pacific RAMP efforts include interdisciplinary monitoring of oceanographic conditions, coral reef habitat assessments and mapping. Most data are available upon request.

For more information
Coral Reef Conservation Program
Pacific Islands Fisheries Science Center
CRED publications
CRED monitoring reports
CRED fish team
Fish team lead and fish survey data requests: ivor.williams@noaa.gov, adel.heenan@noaa.gov