A Better Understanding of Coral Reef Ecosystems

Pelagic predators such as these barracuda, Sphyraena qenie, are part of the coral reef ecosystem in the U.S. Line Islands (NOAA Photo by Kevin Lino).
A team of scientists have embarked from Hawai'i on a three-month survey of coral reef ecosystems at Johnston Atoll, the U.S. Phoenix Islands, the islands of American Samoa, and the U.S. Line Islands in the tropical Pacific Ocean. The overarching objective is to better understand the coral reef ecosystems of these areas, many of which are seldom explored. The research expedition is part of a regular monitoring program, conducted by the Coral Reef Ecosystem Division (CRED), headquartered in Honolulu, Hawai'i. The expedition is supported by NOAA's Coral Reef Conservation Program and involves extensive cooperation among NOAA scientists and research partners, including the University of Hawaii Joint Institute for Marine and Atmospheric Research (JIMAR), the U.S. Fish and Wildlife Service, San Diego State University, and the Papahānaumaokuākea Marine National Monument.

The research expedition will be carried out from February 27 to May 24, 2012 aboard the NOAA ship Hi'ialakai. Under the leadership of Chief Scientists Dr. Jill Zamzow, Dr. Bernardo Vargas-Angél, and Jamison Gove, a diverse team of researchers will be conducting multidisciplinary coral reef ecosystem surveys, assessing the status of fishes, corals, algae, marine invertebrates, and the oceanographic conditions in which these organisms exist. The scientific data collected during the three-month research expedition will enable informed and effective implementation of ecosystem-based management and conservation strategies for coral reef ecosystems, helping to ensure their protection for generations to come.

Tuesday, April 6, 2010

Predator Dominated Reefs

By Brian Zgliczynski
Typical reef scene at Jarvis Island with large-bodied predatory species
patrolling the reef.
If you could ask any of the scientists aboard the Hi'ialakai to describe what it's like to dive at Jarvis Island, you would hear something like: “mind-blowing, intimidating, exhilarating, intense, eye-opening“.  If you heard these words alone you would think we were out here in the central Pacific filming an energy drink commercial, or certainly something other than conducting scientific research.  However, this is definitely not the case, and Jarvis Island is all of this, and more. The first thing we notice upon arriving at a dive site are ominous shadows circling below. As we perform pre-dive checks and review survey protocols, you can’t help but wonder what awaits. The few minutes just before a dive can be filled with anticipation, and quite an adrenaline rush.

Predatory species like jacks and sharks
are abundant at Jarvis
Upon entering the water the ecological monitoring team is greeted by numerous predatory fishes such as grey reef  sharks (Carcharhinus amblyrhynchos), twinspot snapper (Lutjanus bohar), black trevally (C. lugubris) , and coral grouper (Cephalopholis miniata).  Large-bodied predatory species, which are common at Jarvis, are becoming increasingly rare throughout the tropical Pacific with fisheries exploitation exerting direct impact on reef-fish communities. Predatory species play an integral role in structuring coral reefs and the systematic removal of these important species can have detrimental impacts to the ecosystem.

CRED divers conduct surveys recording species composition as well as the number and size of all fishes observed in a predefined area.  These data are converted into measures of abundance and biomass and used to estimate fish populations around an island or reef.  At Jarvis, predatory species are highly abundant and account for over half of total fish biomass.  Reef scenes like the one pictured above are commonplace. To put this into perspective, Jarvis has about 300 times more predatory fish biomass than the entire island of Oahu.  The research conducted here has altered our perspective of the typical trophic pyramid in which predators (tertiary consumers) comprise a small fraction of total fish biomass in a reef ecosystem. At Jarvis Island, the trophic pyramid is inverted, with top predators accounting for a majority of fish biomass.
Trophic pyramids with species divided into their respective trophic categories.
Tertiary consumers = top-level predatory species, planktivores = species that
feed on microscopic organisms, Secondary consumers = lower-level carnivorous
species, and Primary consumers = herbivores. The Pyramid to the left represents
a degraded system with few predators (tertiary consumers) while the pyramid to
the right represents what researchers have observed at Jarvis Island,
where predators are highly abundant.
As predator dominated coral reef ecosystems become increasingly rare in most parts of the world, contemporary ecological studies concentrate efforts on systems that have already been degraded.  However, Jarvis Island and other U.S. Pacific islands represent some of the remaining examples of ecosystems in their natural state.  Such systems provide an ecological baseline and an unprecedented opportunity for marine scientists to understand what ‘pristine’ coral reef ecosystems are like, aiding in the formulation of appropriate metrics necessary for developing effective ecosystem-based management and recovery plans towards the future.


  1. How does the percentage of predatory biomass at Jarvis compare to Cocos Islands and other areas with high levels of predatory biomass.

  2. I really like turtles and dolphins. I am thinking about becoming an animal trainer at Sea World. Do you ever see dolphins or turtles out there?

  3. Response from Brian Zgliczynski, Fish Biologist:

    Having conducted similar surveys throughout the tropical Pacific including Cocos Island (Costa Rica), the predatory biomass densities observed at Jarvis are among the highest. Additionally, all of the sites where predatory species are abundant display similar inverted trophic pyramids with predatory species accounting for the largest proportion of total fish biomass.

  4. Dolphins and turtles are common at each of the islands we'll be visiting on this expedition. Check out the most recent picture posted for "Cool Thing of the Day" to see a photograph of a green sea turtle from Jarvis Island. The best of luck to you in your pursuit to becoming an animal trainer at Sea World. Marine science is an exciting field to enter, I'm sure you'll love it!

  5. Does illegal fishing occur in the waters around Jarvis and what impact does it have on the trophic pyramid?

  6. How will global warming imact Jarvis Island?

  7. In reference to your post that "Jarvis has about 300 times more predatory fish biomass than the entire island of Oahu." What are the factors that reduce the predatory fish volumes in Oahu?