A Fish That Shapes The Reef

By Andrew E. Gray

Every three years, scientists from NOAA’s Coral Reef Ecosystem Program (CREP) visit Wake Atoll to survey corals, assess the fish populations, and collect oceanographic data for a long-term monitoring effort—the Pacific Reef Assessment and Monitoring Program (Pacific RAMP). Wake Atoll has clear water, healthy coral reefs, and is managed and conserved as part of the expansive U.S. Pacific Remote Islands Marine National Monument. It has a healthy reef fish community with plentiful sharks, jacks, and groupers. As a fish research diver, it’s my kind of paradise. Sitting in the middle of the subtropical North Pacific Ocean, 1,500 miles east of Guam and about 2,300 miles southwest of Honolulu, it may be the most remote place I’ve ever been. But for me, and a few other scientists lucky enough to visit the island, there is one thing that makes Wake a special place: Bolbometopon muricatm, the Bumphead parrotfish.

Bumphead parrotfish

Bumphead parrotfish (Bolbometopon muricatm) at Wake Atoll (Photo: NOAA Fisheries/Andrew E. Gray)

Bumphead parrotfish are an incredible and unique reef fish, differing from other parrotfish by their large size, appearance, diet, and by their ecological impact on coral reef ecosystems. There are a number of other parrotfish that sport a bump on their head, and these may be mistaken for a Bumphead parrotfish—that is until you actually see one. Bumpheads have a presence like no other fish on the reef and when they are around I can’t take my eyes off of them. The first thing I notice is their sheer size: growing to 4.2 feet long and up to a 100 pounds (that’s 130 cm and 46 kg for you scientists). Bumpheads are the world’s largest parrotfish and among the largest of all reef fish. When I get a little closer, I can’t help but focus on their incredible beaks. On coral reefs, all parrotfish species are tasked with the important job of keeping algae from overgrowing reef-building corals.

Corals chomped

Bumphead parrotfish chomp corals and help maintain the health and diversity of the reef ecosystem, Wake Atoll (Photo: NOAA Fisheries/Andrew E. Gray)

Parrotfish bite and scrape algae off of rocks and dead corals with their parrot-like beaks; grind the inedible calcium carbonate (reef material made mostly of coral skeletons) which is excreted as sand back onto the reef. Larger parrotfish species can take small chunks out of the reef, removing algae and the occasional piece of coral. Bumphead parrotfish are unique in that they are continuously crunching large bites out of the reef, about half of it from live coral. In fact, that’s what they do most of the day. Bite the reef. Excrete sand. Repeat. Over the course of a year a single fish can remove over 5 tons of calcium carbonate from the reef! But by selectively eating fast growing coral species over slower growing species, they help maintain a more diverse coral reef ecosystem. Also, by munching down tons of dead corals every year each fish makes room for young corals to settle, grow and build up the reef. This means breaking down “dead reef” into sand rather than it breaking off in a storm and damaging other parts of the reef. And since Bumpheads often travel in groups, sometimes numbering into hundreds and traveling multiple kilometers in a day, this species can have quite an impact on the reef ecosystem. Bumphead parrotfish literally shape the reef.

Bumphead

Large bump on the head of a Bumphead parrotfish (Photo: NOAA Fisheries/Andrew E. Gray)

Then, of course, there is the fish’s namesake, its bump. All Bumphead parrotfish sport a large protrusion on their forehead which is similar in function to a pair of horns on a bighorn sheep. The largest males have the biggest bumps and will occasionally use them as battering rams around spawning time, smashing headfirst into rivals in an attempt to show their dominance and retain territorial and breeding rights. This incredible behavior was observed by CREP scientists in 2009 and first documented and filmed by researchers at Wake in 2011. During these mating events, the parrotfish gather or aggregate around a spawning site and can number into the hundreds, an uncommon site anywhere in the world and one that I hope to see sometime at Wake.

Historically, Bumphead parrotfish were plentiful throughout much of the Western Pacific, Indian Ocean, and Red Sea. In recent decades, fishing led to sharp declines in abundance and they are now only common in protected or very remote areas. Bumpheads have a few traits that make them particularly vulnerable to overfishing, which has led to local disappearances in many parts of their range. Bumphead parrotfish can live to be 40 years old; they do not reach sexual maturity until 5-8 years old and likely have low natural mortality as adults so there is not high natural turnover in the population. However, most detrimental to their survival in a human-dominated world is their aggregating behavior and preference for shallow water. Groups of Bumpheads could be easily netted, as they feed during the day, and at night sleeping parrotfish are easy targets for spear fishermen. With the introduction of scuba gear in the 1960’s and 1970’s there was a steep decline in Bumphead abundances as entire schools could be removed in a single night while they slept. Juvenile Bumpheads are also hard to find or study throughout much of their range and raises concerns that some adult populations are too far from juvenile habitats. This distance prevents new youngsters from entering the population to replace adults that have been caught. In areas where juveniles can be commonly found, such as Papua New Guinea and the Solomon Islands, they are associated with mangrove, rubble, and sheltered lagoon habitats. And this is why Wake Atoll may be such a hotbed of Bumpheads.

Reef at Wake Atoll

Coral reef at Wake Atoll in the Pacific Remote Islands Marine National Monument (Photo: NOAA Fisheries/James Morioka)

In addition to having a sizable healthy coral reef around the island, Wake Atoll has an expansive, sheltered lagoon. This may be the perfect habitat for the juvenile parrotfish and allows Wake to have a healthy, self-supplying population of Bumpheads. And since Wake is protected from fishing, it may be as close to a pristine home as the Bumphead parrotfish are going to encounter in today’s world. Wake actually has the highest concentration of Bumphead parrotfish in U.S. waters and possibly the world (although certain areas of the Great Barrier Reef in Australia also have very healthy adult populations). During my time at Wake Atoll, I had a number of chances to see them, from loose groups of just a few individuals, to a school of thirteen.

School too

School of Bumphead parrotfish at Wake Atoll (Photo: NOAA Fisheries/Andrew E. Gray)

As I write this, the NOAA Ship Hi‘ialakai heads west to Guam, our next survey site where I’ll be spending 8 days surveying reef fish. Bumpheads were once thought to be extinct around Guam due to overfishing, but there have been a few sightings by CREP and partners in the past few years, of both adults and juveniles. So while my expectations of encountering these giant bulbous-headed, coral-chomping fish are low, I sure hope I do, given how important they are to the natural function of coral reef ecosystems.

References
  1. Bellwood, D., & Choat, J. (2011). Dangerous demographics: the lack of juvenile humphead parrotfishes Bolbometopon muricatum on the Great Barrier Reef. Coral Reefs, 30(2), 549-554.
  2. Bellwood, D. R., Hoey, A. S., & Choat, J. H. (2003). Limited functional redundancy in high diversity systems: resilience and ecosystem function on coral reefs. Ecology Letters, 6(4), 281-285.
  3. Bellwood, D. R., Hoey, A. S., & Hughes, T. P. (2011). Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs. Proceedings of the Royal Society B: Biological Sciences. doi: 10.1098/rspb.2011.1906
  4. Donaldson, T. J., & Dulvy, N. K. (2004). Threatened fishes of the world: Bolbometopon muricatum (Valenciennes 1840)(Scaridae). Environmental Biology of Fishes, 70(4), 373-373.
  5. Green, A. L., & Bellwood, D. R. (2009). Monitoring functional groups of herbivorous reef fishes as indicators of coral reef resilience: a practical guide for coral reef managers in the Asia Pacific Region: IUCN.
  6. Kobayashi, D., Friedlander, A., Grimes, C., Nichols, R., & Zgliczynski, B. (2011). Bumphead parrotfish (Bolbometopon muricatum) status review. NOAA Technical Memorandum NMFS-PIFSC-26. NOAA.
  7. Muñoz, R. C., Zgliczynski, B. J., Laughlin, J. L., & Teer, B. Z. (2012). Extraordinary Aggressive Behavior from the Giant Coral Reef Fish, Bolbometopon muricatum, in a Remote Marine Reserve. PLoS One, 7(6), e38120. doi: 10.1371/journal.pone.0038120
  8. Munoz, R. C., Zgliczynski, B. J., Teer, B. Z., & Laughlin, J. L. (2014). Spawning aggregation behavior and reproductive ecology of the giant bumphead parrotfish, Bolbometopon muricatum, in a remote marine reserve. PeerJ, 2, e681.
  9. Sundberg, M., Kobayashi, D., Kahng, S., Karl, S., & Zamzow, J. (2015). The Search for Juvenile Bumphead Parrotfish (Bolbometopon muricatum) in the Lagoon at Wake Island.

Four Million Nine Hundred Ninety-Nine Thousand Nine Hundred and Ninety-Nine

By Kevin Lino

Five million… that number has a pleasant vastness to it. Five million of anything seems overwhelming. Try to picture five million fish. Start small and keep expanding. How would that look? Would they be one compact bait ball of iridescent shapes or a colorful patch work of reef fish schooling together? Well, it would take years to count that high and yet here we stand (or swim) just a few thousand fish away from reaching this landmark.

Image 1: A school of Big Eye Jack (Caranx sexfasciatus) trail behind a towed diver during a survey. Photo by Kevin Lino

Image 1: A school of Big Eye Jack (Caranx sexfasciatus) trail behind a towed diver during a survey. Photo by Kevin Lino

Image 2: Map of Study Region for Jarvis Island, Palmyra Atoll, and Kingman Reef.

Image 2: Map of Study Region for Jarvis Island, Palmyra Atoll, and Kingman Reef.

For the PIFSC Coral Reef Ecosystem Division (CRED) fish team, it has taken 15 years of dedicated hard work under the ocean’s surface to get to this point. This happens as our team collects visual census data on reef fish populations throughout the US-affiliated Pacific Islands. As part of the Pacific Reef Monitoring and Assessment Program (RAMP) these surveys support the National Coral Reef Monitoring Program (NCRMP). The goal of our research missions is to conduct integrated, consistent, and comparable monitoring of coral reefs across all regions while assessing and detecting change in natural resources. This is true around large inhabited islands like Tutuila in American Samoa, where we recently completed surveys, well as the tiny remote atolls in the Line Islands chain where we are currently working.

Image 3: A Scalloped Hammerhead Shark (Sphyrna lewini) cruises the bottom amongst schools of anthias at Jarvis Island. Photo by Kevin Lino

Image 3: A Scalloped Hammerhead Shark (Sphyrna lewini) cruises the bottom amongst schools of anthias at Jarvis Island. Photo by Kevin Lino

Image 4: Diver Marie Ferguson tows over a school of anthias at Jarvis Island. Photo by Kevin Lino

Image 4: Diver Marie Ferguson tows over a school of anthias at Jarvis Island. Photo by Kevin Lino

To date, the division has counted 4,890,980 fish throughout our survey areas using several methods. While it is hard to know which method will be used to count the five millionth fish, our primary surveys are conducted by stationary point count (SPC) divers who use a transect line along the seafloor counting every species in that area. Another team is towed behind a small boat counting the larger (over 50 cm) more mobile species– circumnavigating the islands and covering up to 15km each day. Odds are in the favor of the SPC diver to get the count with one of the smaller species that school in their many of thousands, quite likely a cute little 3 cm Chromis vanderbilti. Either way, it is a major landmark for our program and we look forward to seeing which lucky diver will count that fish.

Image 5: A small school of Chromis vanderbilti huddle near the seafloor. Photo by Kevin Lino

Image 5: A small school of Chromis vanderbilti huddle near the seafloor. Photo by Kevin Lino

Our first stop, Jarvis Island, is one of the most pristine reef environments I have ever seen. In the waters surrounding the mostly barren sands above, is a flourishing ecosystem partially driven by upwelling of cold and nutrient rich water from deeper in the ocean. In such productive waters, tens or even hundreds of large sharks, jacks, and manta rays are likely to appear alongside our divers the moment they enter the water. Just off the bottom, the real work begins as thousands of anthias, chromis, and other small species abound in the rugose benthos of healthy corals and algae. After six days at Jarvis, we voyage north toward the masses of fish at Palmyra Atoll and Kingman Reef for the last 12 days of surveys. Both of these remote areas are also quite unique, hosting an abundance of biodiversity to keep divers busy, while getting closer to that fortunate five millionth fish.

We are grateful for the nearly 80 scientists who have worked together to get us this far. One of whom has counted nearly 500,000 more fish than her next highest counterpart. In the last decade working with CRED, Paula Ayotte has rarely missed an opportunity to go to sea and spend hours underwater during these missions. If we had a Hall of Fame, she would be inducted unanimously for so many reasons: not only for counting nearly a million fish on her own, but also for making sure all other divers are trained, and mostly for being the most entertaining dive buddy you could hope for. It has been a pleasure working with her for that time and while it would be nice to be the diver to count the 5,000,000 fish… I’m hoping that Paula gets that count with a three meter manta ray at Jarvis.

Image 6: A Giant Manta (Manta birostris) curiously swims over a diver during a survey. Photo by Kevin Lino

Image 6: A Giant Manta (Manta birostris) curiously swims over a diver during a survey. Photo by Kevin Lino

Image 7: Diver Paula Ayotte amongst a healthy school of Whitebar Surgeonfish (Acanthurus leucopareius) and Convict Tang (A. triostegus) while conducting an SPC dive.

Image 7: Diver Paula Ayotte amongst a healthy school of Whitebar Surgeonfish (Acanthurus leucopareius) and Convict Tang (A. triostegus) while conducting an SPC dive.

Reefs for the future: Resilience of coral reefs in the main Hawaiian Islands

By Brett Schumacher
Antler Coral (Pocillopora eydouxi) provides habitat for a number of fish, crabs and other animals but is susceptible to bleaching.

Antler Coral (Pocillopora eydouxi) provides habitat for a number of fish, crabs and other animals but is susceptible to bleaching.

Declining health of coral reef ecosystems led scientists to search for factors that support reef resilience: the ability of reefs to resist and recover from environmental disturbance. Scientists recently identified 11 measurable factors that affect the resilience of coral reefs (Table 1) (McClanahan et al. 2012). Reef resilience factors include characteristics of the coral assemblage, populations of fish that live on the reef, land use practices, and water temperature variability. These factors were used to conduct a quantitative assessment of the resilience potential of reefs across the main Hawaiian Islands (MHI).

Table 1. List of resilience factors, measures used for evaluation, and sources of data.  (Boldface indicates factors that can be directly influenced by local management.)

Table 1. List of resilience factors, measures used for evaluation, and sources of data.
(Boldface indicates factors that can be directly influenced by local management.)

Locations of Rapid Ecological Assessment (REA) surveys conducted by the NOAA Pacific Islands Fisheries Science Center’s Coral Reef Ecosystem Division (CRED) from 2010 to 2013 were used to designate study units called “georegions” (Figure 1). Watersheds upstream of georegions were then grouped to delineate the area that could affect adjacent reefs through pollution, runoff, and sedimentation. REA surveys provided data to evaluate biological/ecological resilience factors, and external data sources were used to inform physical and environmental factors not directly measured by CRED (Table 1). Data for each factor was compiled, normalized, and averaged to produce a composite resilience score for each georegion.

Figure 1. Composite resilience scores: Colors indicate the score for each georegion and encompass watersheds which drain onto the reef. Dots indicate locations of NOAA CRED in-water rapid ecological assessment surveys.

Figure 1. Composite resilience scores: Colors indicate the score for each georegion and encompass watersheds which drain onto the reef. Dots indicate locations of NOAA CRED in-water rapid ecological assessment surveys.

Twenty-nine georegions were analyzed across the MHI. Lowest composite resilience scores were earned by reefs near densely populated areas on O‘ahu, while highest scores were earned near relatively sparsely populated areas of other islands (Figure 1).

A key aspect of the reef resilience framework is that it can empower local action to improve resilience of coral reefs because some drivers of resilience are heavily influenced by large-scale climatic forces, while others can be directly affected by local management (Table 1). For example, land use practices and marine resource stewardship will affect watershed health and herbivorous fish biomass, respectively.

Figure 2. Comparison of resilience factors that can be influenced by local action vs. those that cannot.

Figure 2. Comparison of resilience factors that can be influenced by local action vs. those that cannot.

Herbivorous fish such as uhu (parrotfish) support resilient reefs by reducing macroalgae abundance. Uhu species shown are Bullethead Parrotfish (Chlorurus spilurus) above and Palenose Parrotfish (Scarus psittacus) below.

Herbivorous fish such as uhu (parrotfish) support resilient reefs by reducing macroalgae abundance. Uhu species shown are Bullethead Parrotfish (Chlorurus spilurus) above and Palenose Parrotfish (Scarus psittacus) below.

Figure 2 compares the mean score of locally manageable factors to other factors for each georegion. If a region falls below the comparison line, locally managed scores are low relative to other scores, and resilience could be improved through targeted management action. Factors influenced by local management often scored relatively low, so most georegions in the MHI are below this line. However, each island has areas which fall near the comparison line.

The range in scores affords local management different avenues to address reef resilience. For example, georegions near or above the line could be prioritized to maintain reef resilience, or efforts could be focused on georegions below the line to improve their resilience.

Diseases such as the Black Band Disease afflicting this Rice Coral (Montipora capitata) undermine the resilience of coral reefs.

Diseases such as the Black Band Disease afflicting this Rice Coral (Montipora capitata) undermine the resilience of coral reefs.

Acknowledgement: This work was funded through a grant from the NOAA Coral Reef Conservation Program.

For additional information on resilience scores or citations, please contact: nmfs.pic.credinfo@noaa.gov

This publication may be referenced as: PIFSC. 2014. Reefs for the future: Resilience of coral reefs in the main Hawaiian Islands. NOAA Fisheries Pacific Science Center, PIFSC Special Publication, SP-15-001, 2p.