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.

FIG2_SPC

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).

FIG5_FishBiomass

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).

FIG6_PercentCover

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.

FIG7_shark

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.

References
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.

 

The fastest divers you’ve ever seen: installation of a climate monitoring station at Pagan Island

Text and video by Noah Pomeroy

I wish we could actually move as fast as we do in this video! In reality, this time-lapse video captures a scuba dive that took place on April 23 over about one hour in real time during a recent Pacific Reef Assessment and Monitoring Program (Pacific RAMP) research cruise in the Mariana Archipelago. This video shows the Climate and Ocean Change Team of the PIFSC Coral Reef Ecosystem Division (CRED) establishing a 15-m-deep climate monitoring station at Pagan Island in the Commonwealth of the Northern Mariana Islands (CNMI).

 

This site and other climate monitoring stations feature a variety of instrumentation, including subsurface temperature recorders (STRs), autonomous reef monitoring structures (ARMS), calcification accretion units (CAUs), and bioerosion monitoring units (BMUs). These instruments and monitoring installations provide oceanographic and ecological information about coral reef ecosystems. Seawater temperature is measured by STRs, calcification and bioerosion rates are determined by CAUs and BMUs, and cryptic biodiversity is evaluated by the analysis of invertebrate communities found living within ARMS.

The work at each station involves other activities in addition to the installation of instruments. During this dive, we completed a survey of rugosity, or habitat complexity, to document the physical relief of the reef structure. We also performed a photoquad survey, taking photographs along a transect to document the benthic reef community. Water samples were collected to assess the carbonate chemistry of water at the reef and at the surface above it.

Conducting this much work during one dive requires a lot of pre-dive planning and in-water choreography. Before beginning such a scuba dive, each diver identifies the tasks that he or she will complete and makes sure to have all the necessary tools and instruments. Although the team works to execute the dance as planned, unexpected challenges are common underwater. Heavy surge (the back and forth motion of water due to frequent waves) or a very hard substrate can make installing instruments and conducting a reef survey difficult.

Climate monitoring stations are one component of the broad National Coral Reef Monitoring Plan (NCRMP) of NOAA’s Coral Reef Conservation Program (CRCP). The NCRMP philosophy is to collect a standard suite of oceanographic and ecological information throughout each of NOAA’s jurisdictions to establish baselines and assess temporal and spatial variability in these coral reef ecosystems caused by global climate change and ocean acidification.

Ocean acidification is the changing of the carbonate chemistry of Earth’s oceans due to absorption of carbon dioxide (CO2). This absorption changes their delicate chemical balance, making it difficult for calcifying organisms, such as corals, mollusks, and shellfishes, to produce their carbonate skeletons. Information gathered at climate monitoring stations will be used by CRED staff to examine how the temperature and chemistry of the waters surrounding reefs vary over time and space and how those changes effect the fishes, corals, algae, and other organisms of the coral reef ecosystems at those sites.

The CRED so far has established climate monitoring stations in the CNMI and Guam, at Wake Island, and throughout the Hawaiian Archipelago. In 2015, the CRED will establish stations in American Samoa and at islands and atolls that make up the Pacific Remote Islands Marine National Monument. Support for these climate stations as part of NCRMP comes from the CRCP and the NOAA Ocean Acidification Program.

Four scuba divers from the PIFSC Coral Reef Ecosystem Division are featured in this video: Jeanette Clark, Russell Reardon, Charles Young, and Noah Pomeroy.

 

Coral reef monitoring in the Mariana Archipelago: preliminary results from visual surveys of fishes and benthic habitats

By Kathryn Dennis and Bernardo Vargas-Ángel

The PIFSC cruise HA-14-01 officially concluded yesterday, Monday, June 2, when the NOAA Ship Hi`ialakai arrived back at Ford Island, Pearl Harbor, from Saipan. During this expedition, which began on March 5, scientists from the PIFSC Coral Reef Ecosystem Division (CRED) and partners conducted ecological surveys, collected water samples, and deployed monitoring instruments and platforms at Wake Island and in the Mariana Archipelago as part of the CRED-led Pacific Reef Assessment and Monitoring Program (Pacific RAMP). As a part of the National Coral Reef Monitoring Plan of NOAA’s Coral Reef Monitoring Program, researchers established climate monitoring stations at 4 islands in the Mariana Archipelago and at Wake Island, where integrated activities provide for long-term collection of data on ocean temperature, chemical composition, benthic cover, calcification, bioerosion, and biodiversity to monitor the effects of climate change and ocean acidification.

The volcano on the island of Pagan emits plumes of gas and steam on the evening of April 20, as seen in this photo taken during the PIFSC cruise HA-14-01. NOAA photo

The volcano on the island of Pagan emits plumes of gas and steam on the evening of April 20, as seen in this photo taken during the PIFSC cruise HA-14-01. NOAA photo

From March 25 to May 6, during Legs II and III and part of Leg I of this latest research cruise at Guam and the Commonwealth of the Northern Mariana Islands (CNMI), CRED scientists and partners completed 100 broad-scale towed-diver surveys, covering more than 220 km of coastline and, at Rapid Ecological Assessment (REA) sites, conducted 329 fish surveys and 158 benthic surveys. Members of the CRED Climate and Ocean Change Team installed 15 climate monitoring stations around Guam, Saipan, Pagan, and Maug, deploying 15 subsurface temperature recorders (STRs), 55 calcification accretion units (CAUs), 45 autonomous reef monitoring structures (ARMS), and 75 bioersion monitoring units (BMUs)—in addition to installations of 70 CAUs at supplementary monitoring sites and 55 STRs at strategic locales associated with climate monitoring stations and long-term (>9 years) time series. For a summary of activities conducted and preliminary results from REA surveys at Wake Island during Leg I, go to the previous blog post published on April 10.

A cursory review (prior to the data being fully analyzed) did not reveal any observations of notable changes in the structure of the fish and benthic communities, in comparison with survey results from the previous Pacific RAMP cruise in the Mariana Archipelago in 2011, at Rota, Aguijan, Tinian, Saipan, Sarigan, Guguan, Alamagan, Pagan, Asuncion, Maug, and Farallon de Pajaros in the CNMI or at Guam are reported at this time. However, unusual cold-water temperatures (~17°C) were experienced at Asuncion, Maug, and Farallon de Pajaros, as was volcanic activity that originated mainly from Ahyi Seamount located nearly 18 km southeast of Farallon de Pajaros.

Preliminary results from the surveys at REA sites of fishes and benthic habitat conducted at depths of 0–30 m by scuba divers from the CRED Fish Ecology Team during the PIFSC cruise HA-14-01 are provided in the fish monitoring brief below. The islands on the Mariana Arc can be divided into 2 groups: the old southern islands and the young, volcanic northern islands. The summary below also was published on May 23 (and is available for download) as 2 separate 2-page PIFSC Data Reports, one for the southern islands of this archipelago and the other for the northern islands.

Pacific Reef Assessment and Monitoring Program
Fish monitoring brief: Mariana Archipelago 2014

By Adel Heenan

About this summary brief

The purpose of this document 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 monitoring program known as the Pacific Reef Assessment and Monitoring Program (Pacific RAMP). More detailed survey results will be available in a forthcoming annual status report.

Sampling effort in the southern islands

  • Ecological monitoring took place in the southern Mariana Archipelago from March 25 2014 to May 07 2014.
  • Data were collected at 178 sites. Surveys were con- ducted at Saipan (n=11), Tinian (n=19), Aguijan (n=10), Rota (n=28), and Guam (n=73).
  • At each site, the fish assemblage was surveyed by underwater visual census and the benthic community was assessed.

Sampling effort in the northern islands

  • Ecological monitoring took place in the northern Mariana Archipelago from April 19 2014 to May 06 2014.
  • Data were collected at 148 sites. Surveys were conducted at Farallon de Pajaros (FDP) (n=11), Maug (n=40), Asuncion (n=21), Pagan (n=43), Alamagan (n=11), Guguan (n=11), and Sarigan (n=11).
  • At each site, the fish assemblage was surveyed by underwater visual census and the benthic community was assessed.

Overview of data collected

Figure 1. Mean total fish biomass at sites surveyed in the southern islands.

Figure 1. Mean total fish biomass at sites surveyed in the southern islands.

Figure 2. Mean total fish biomass at sites surveyed in the northern islands.

Figure 2. Mean total fish biomass at sites surveyed in the northern islands.

Figure 3. Mean hard coral cover at sites surveyed in the southern islands.

Figure 3. Mean hard coral cover at sites surveyed in the southern islands.

Figure 4. Mean hard coral cover at sites surveyed in the northern islands.

Figure 4. Mean hard coral cover at sites surveyed in the northern islands.

Preliminary results for fish biomass also are presented by consumer group and size class. 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 5. Mean consumer group fish biomass (± standard error) at sites surveyed in the southern islands. Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 5. Mean fish biomass (± standard error) by consumer group at sites surveyed in the southern islands. Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 6. Mean consumer group fish biomass (± standard error) at sites surveyed in the northern islands. Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 6. Mean fish biomass (± standard error) by consumer group at sites surveyed in the northern islands. Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 7. Mean fish biomass per size class (± standard error) at sites surveyed in the southern islands. Fish measured by total length (TL) in centimeters (cm).

Figure 7. Mean fish biomass per size class (± standard error) at sites surveyed in the southern islands. Fish measured by total length (TL) in centimeters (cm).

Figure 8. Mean fish biomass per size class (± standard error) at sites surveyed in the northern islands. Fish measured by total length (TL) in centimeters (cm).

Figure 8. Mean fish biomass per size class (± standard error) at sites surveyed in the northern islands. Fish measured by total length (TL) in centimeters (cm).

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 (Fig. 9). 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 generally will be pooled to improve island-scale estimates.

Each diver also conducts a rapid visual assessment of reef composition, by estimating the percent cover of major benthic functional groups (encrusting algae, fleshy 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 line at each site that are archived to allow for future analysis.

Figure 9. Method used to monitor fish assemblage and benthic communities at the Rapid Ecological Assessment (REA) sites.

Figure 9. Method used to monitor fish assemblage and benthic communities at Rapid Ecological Assessment (REA) sites.

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: http://coralreef.noaa.gov

Pacific Islands Fisheries Science Center: http://www.pifsc.noaa.gov/

CRED publications: http://www.pifsc.noaa.gov/pubs/credpub.php

CRED fish team: http://www.pifsc.noaa.gov/cred/fish.php

Fish team lead and fish survey data requests: ivor.williams@noaa.gov

 

To download a PDF file of PIFSC Data Report DR-14-009, the fish monitoring brief for the southern islands of the Mariana Archipelago, click here.

To download a PDF file of PIFSC Data Report DR-14-010, the fish monitoring brief for the northern islands of the Mariana Archipelago, click here.

 

Update from the Mariana Archipelago: monitoring cruise completes work in the southern islands

By Bernardo Vargas-Ángel
The NOAA Ship Hi`ialakai, seen off the coast of Anatahan, a northern island in the Commonwealth of the Northern Mariana Islands, during a previous monitoring cruise in the Mariana Archipelago in May 2009. NOAA photo by Bernardo Vargas-Ángel

The NOAA Ship Hi`ialakai, seen off the coast of Anatahan, a northern island in the Commonwealth of the Northern Mariana Islands, from a small boat during a previous monitoring cruise in the Mariana Archipelago in May 2009. NOAA photo by Bernardo Vargas-Ángel

On April 17, the NOAA Ship Hi`ialakai departed Saipan Harbor and began Leg III of the PIFSC cruise HA-14-01 with a few more days of monitoring operations around Saipan before transiting to the island of Sarigan. With work essentially complete in the southern islands of the Mariana Archipelago, the Hi`ialakai had been in port in Saipan Harbor for a short, 3-day pause between legs of this Pacific Reef Assessment and Monitoring Program (Pacific RAMP) expedition. Activities to monitor coral reef ecosystems of the Commonwealth of the Northern Mariana Islands (CNMI) began on April 5 during Leg II of this cruise and work around Guam took place on March 25–April 4, primarily during Leg I. Led by the PIFSC Coral Reef Ecosystem Division (CRED), this mission marks the 6th monitoring cruise in Guam and the CNMI by staff from PIFSC and partner agencies since 2003.

Around Guam, Rota, Aguijan, Tinian, and Saipan Islands, CRED scientists on March 25–April 18 conducted ecosystem surveys of fishes, benthic and coral communities, and microbes and deployed oceanographic instruments and biological installations. During Leg III, which is expected to conclude on May 6, CRED staff will conduct small-boat operations for coral reef ecosystem monitoring at the following northern islands and banks: Sarigan, Zealandia Bank, Guguan, Alamagan, Pagan, Agrihan, Asuncion, Maug, Supply Reef, and Farallon de Pajaros (or Uracas).

On a reef off the coast of Rota Island, divers conduct belt-transect surveys of the benthos on April 8. NOAA photo by Bernardo Vargas-Ángel

On a reef off the coast of Rota Island, divers conduct a belt-transect survey of the benthos on April 8 during the PIFSC cruise HA-14-01, the 6th expedition in the Marina Archipelago since 2003 for the Pacific Reef Assessment and Monitoring Program, which is led by the PIFSC Coral Reef Ecosystem Division. NOAA photo by Bernardo Vargas-Ángel

A diver on April 13 collects digital images of reef benthos along a transect at a Climate Monitoring Station off the cost of Saipan. NOAA photo

A diver on April 13 collects digital still photographs of the reef benthos along a transect at a Climate Monitoring Station off the cost of Saipan. Such benthic images can be analyzed to characterize benthic habitat and estimate percent cover of key functional groups. NOAA photo

At Rapid Ecological Assessment (REA) sites, surveys for reef fishes document species richness, abundance, and sizes, and surveys of benthic and coral communities study the percent composition of bottom-dwelling organisms in addition to the densities, sizes, and health conditions of coral colonies. During broad-scale towed-diver surveys, divers record observational data on large-bodied fishes (>50 cm total length), percent composition of the seafloor, coral stress, and conspicuous invertebrates. Studies of microbial communities document the diversity and abundance of bacteria and viruses and their interactions with coral reefs.

This mission also includes studies of the diversity of cryptic invertebrates; collection of data on water temperature, salinity, carbonate chemistry, and other physical characteristics of coral reef environments; and assessment of the potential early effects of ocean acidification on cryptobiota (e.g., small, hidden organisms) and the rates of reef carbonate deposition and coral calcification.

Researchers of the PIFSC Coral Reef Ecosystem Division use trays, like the one in this photo taken on April 13, to sort the cryptic reef invertebrates that they collect from autonomous reef monitoring structures (ARMS) retrieved during this current cruise from the nearshore locations where they had been deployed in 2011 during the previous Pacific Reef Assessment and Monitoring Program expedition in the Mariana Archipelago. NOAA photo

Researchers of the PIFSC Coral Reef Ecosystem Division on April 13 use this tray and others to sort the cryptic reef invertebrates that they collect from the autonomous reef monitoring structures (ARMS) retrieved during this current cruise from the nearshore locations where they had been deployed in 2011 during the previous Pacific Reef Assessment and Monitoring Program expedition in the Mariana Archipelago. NOAA photo

Thus far across the 5 southern Mariana Islands, including work on April 17, CRED researchers during this cruise have completed 66 towed-diver surveys along a combined 130 km of coastline and, at REA sites, 153 fish surveys and 62 benthic surveys. The instrumentation team deployed 4 Climate Monitoring Stations around Guam and 3 stations around Saipan, with each station containing arrays of subsurface temperature recorders (STRs), calcification accretion units (CAUs), autonomous reef monitoring structures (ARMS), and bioersion monitoring units (BMUs). Overall, no notable changes in the structure of the fish and benthic communities can be reported at this time for the areas surveyed at Guam or in the southern CNMI, in comparison to survey results from the previous cruise in this region in 2011. Additionally, no widespread coral bleaching or outbreaks of coral diseases or corallivorous crown-of-thorns seastars (Acanthaster planci) were observed.