Species and Habitats

Papahānaumokuākea National Marine Sanctuary is a place of unique marine habitats and wildlife that provide large-scale ecosystem services for the region and the world. The marine habitat includes several interconnected ecosystems, including coral islands surrounded by sunlit reefs (down to 100 feet), low-light mesophotic reefs (100 to 490 feet) with extensive algal beds, open ocean (pelagic) waters connected to the greater North Pacific Ocean, deep-water habitats such as abyssal plains 16,400 feet below sea level, and deep reef habitat characterized by seamounts, banks, and shoals. Explore the pages below to learn about the various ecosystems within the sanctuary and ongoing research of species and habitats.

A Refuge for Protected Marine Species

Many species of plants and animals still exist in Papahānaumokuākea that once occurred in the main Hawaiian Islands (as evidenced by their presence in the fossil record), but could not survive after the arrival of humans and their commensal mammals. In all, there are 23 species found in Papahānaumokuākea that are listed under the U.S. Endangered Species Act, and there are undoubtedly many more that might be eligible for listing. Additionally, Papahānaumokuākea is home to 22 IUCN Red-Listed species and contains countless endemic species found nowhere else in the world, including some with ranges limited to a single atoll.

Papahānaumokuākea provides critical habitat for the in situ conservation of a number of endangered species. Hawaiian monk seals are found only in Hawai‘i, with the main breeding subpopulations located throughout the Northwestern Hawaiian Islands, and a small but growing population in the main Hawaiian Islands. This population represents one of only two monk seal populations remaining anywhere on the planet, as the monk seals of the Caribbean are extinct and the populations of the Mediterranean monk seals are perilously low.

In 1988, NOAA Fisheries designated critical habitat for the Hawaiian monk seal from the shoreline to 20 fathoms (36.5 meters) around every island, atoll, and bank of Papahānaumokuākea, except Sand Island at Kuaihelani (Midway Atoll). This habitat includes "all beach areas, sand spits and islets, inner reef waters, and ocean waters." Each year, NOAA biologists spend multiple months at field camps in teams of three to seven staff per camp at atolls within Papahānaumokuākea. These biologists monitor and protect Hawaiian monk seals by collecting data for stock assessments, tagging pups, and undertaking activities to aid in the recovery of the species.

In addition, the waters of Papahānaumokuākea are home to more than 20 cetacean species, six of them federally and/or internationally recognized as endangered. Papahānaumokuākea National Marine Sanctuary contains two-thirds of the humpback whale's wintering habitat in the Hawaiian Archipelago, and important behaviors such as breeding and calving have been documented within the waters of Papahānaumokuākea. Further, high and sustained seasonal chorusing levels of whale song have been documented across every location sampled in Papahānaumokuākea.

Papahānaumokuākea provides nearly the entire nesting habitat for the threatened Hawaiian green sea turtle. On the undisturbed beaches of these remote atolls, both male and female turtles come ashore to bask on the beach in broad daylight, a behavior no longer seen in most other parts of the world. The critically endangered hawksbill and leatherback sea turtles, and the endangered olive ridley and loggerhead sea turtles, are also found in Papahānaumokuākea.

A Place with High Endemism and Many Species New to Science

There are hundreds, if not thousands, of endemic species thriving within the ecosystems of Papahānaumokuākea—meaning they are found nowhere else in the world. Papahānaumokuākea is the last or only home for these creatures, making continued protection to assure their existence ever-more important.

Scuba surveys in water less than 100 feet have shown an average of 21% of the coral reef fish species observed are endemic. By using advanced technical diving, NOAA divers found that in waters of 100 to 300 feet deep (the 'mesophotic' or deep reef zone), nearly 50% of the fish observed are unique to Hawaiʻi. Incredibly, on some deeper reefs within Papahānaumokuākea, more than 90% of fish observed were endemic species. 100% endemism was documented in the mesophotic reef fish assemblages at depths of 300 feet at Hōlanikū (Kure Atoll)—the highest level of endemism known from any marine ecosystem on Earth.

Papahānaumokuākea is a place of wonder with new marine species waiting to be discovered. Pete Basabe's Butterflyfish (Prognathodes basabei) was described as a new species from specimens collected from deep reefs at Manawai (Pearl and Hermes Atoll) and a new Basslet reef fish, Tosanoides obama, was collected at a depth of 295 feet (90 meters) at Hōlanikū (Kure Atoll). New species of macroalgae have also been discovered on the mesophotic reefs of Papahānaumokuākea National Marine Sanctuary. Office of National Marine Sanctuaries scientists engage with members of the Papahānaumokuākea Native Hawaiian Cultural Working Group, the ‘Ewa Limu Project, and Native Hawaiian cultural practitioners to incorporate Hawaiian names into the formal scientific names for new species discovered in the sanctuary.

At deeper depths than even technical divers can reach, research submersibles have discovered new species within the sanctuary, including a new species of deep-water black coral, Leiopathes annosa, found at depths of 1,000-1,600 feet.

References

Lammers MO, Goodwin B, Kügler A, Zang EJ, Harvey M, Margolina T, Martinez JA, Merkens K, and Hatch LT (2023) The occurrence of humpback whales across the Hawaiian archipelago revealed by fixed and mobile acoustic monitoring. Front. Mar. Sci. 10:1083583. https://doi.org/10.3389/fmars.2023.1083583

Johnston DW, Chapla ME, Williams LE, and Mattila DK (2007) Identification of humpback whale wintering habitat in the Northwestern Hawaiian Islands using spatial habitat modeling, Endang. Species Res. 3:249-257. https://doi.org/10.3354/esr00049

Kosaki RK, Pyle RL, Leonard JC, Hauk BB, Whitton RK, and Wagner D (2017) 100% endemism in mesophotic reef fish assemblages at Kure Atoll, Hawaiian Islands. Oceanarium 47: 783-784. https://doi.org/10.1007/s12526-016-0510-5

Predator-Dominated Coral Reefs

The reef ecosystem of Papahānaumokuākea is known as one of the last remaining predator-dominated reef ecosystems. A predator-dominated reef ecosystem is a reef where large, top-level predators—like sharks, jacks, and groupers—are especially abundant and play a major role in shaping the food web.

Understanding what keeps a predator-dominated reef thriving requires looking at the ecosystem from many angles. Scientists at Papahānaumokuākea National Marine Sanctuary use long-term monitoring to track changes in coral health and composition, fish populations, and the algae that fuel the reef food web. These long-term datasets, paired with studies on storm recovery, bleaching events, predator movements, and genetic connectivity, help reveal how this remote ecosystem works and how it responds to a changing ocean.

Long-Term Monitoring

A core part of studying the marine resources within Papahānaumokuākea National Marine Sanctuary is conducting regular spatial and temporal surveys as part of the reef assessment and monitoring program. Each year, we assess the health of the coral reef ecosystems with a focus on Lalo (French Frigate Shoals), Kapou (Lisianski Island), Kamole (Laysan Island), Manawai (Pearl and Hermes Atoll), Kuaihelani (Midway Atoll), and Hōlanikū (Kure Atoll). Scuba divers identify reef fish to assess biodiversity, count the fishes to measure abundance, and estimate the size of fishes to quantify biomass. They also systematically collect photographs of the reef that are analyzed for percent coral cover and habitat complexity. Using these images, corals and macroalgae can be identified to the species level, prevalence of coral disease and bleaching can be documented, and individual colonies can be counted and sized.

Spatial reef surveys, where we use the same method at many sites around each atoll and across various depths, enable researchers to study how marine resources differ across the vast range of the sanctuary, and to estimate overall reef health metrics for each atoll and depth range. Long-term monitoring, where we survey the same reefs with the same methods year after year, can reveal how marine resources change through time. This includes tracking natural changes in coral and macroalgae cover at healthy reefs without known stressors, as well as at reefs that are recovering from documented stress events such as severe bleaching or storm damage. Our sanctuary monitoring work has been greatly strengthened by partnerships with NOAA's National Coral Reef Monitoring Program and the University of Hawai‘i.

Annual reef monitoring efforts enable researchers to describe patterns in coral reef ecosystems across Papahānaumokuākea National Marine Sanctuary. This includes identifying three general subregions of reef species communities (the northern, middle, and southern atolls), and tracking changes in reef ecosystem health through time.

Long-Term Monitoring Case Studies

Kapou Coral Bleaching

In 2014, the shallow water reefs of Kapou (Lisianski Atoll) experienced a severe coral bleaching event with high coral mortality. Scientists used in-water surveys of reef health paired with structure from motion photogrammetry to build high resolution three-dimensional reef models to track the recovery of these reefs. These repeat surveys have documented the recovery of impacted corals, as well as the presence of young corals and crustose coralline algae (a hard algae that aids in coral recruitment and cementing reef structure).

Hurricane Wakala Recovery at Lalo

Researchers have been following specific reef sites at Lalo (French Frigate Shoals) that were severely damaged by Hurricane Walaka in 2018, which turned these colorful, abundant underwater ecosystems into quiet expanses of rubble. By 2021, scientists documented recruitment by juvenile corals as well as the return of many juvenile and adult fishes. One particularly promising sign is the observation of herbivorous fishes such as manini or convict tang (Acanthurus triostegus) and goldring surgeonfish or kole (Ctenochaetus strigosus), which graze on algae, and keep the dead coral surfaces clean so that new, juvenile corals can take hold and grow.

The Importance of Benthic Algae

To further investigate specific parts of reef health, Papahānaumokuākea National Marine Sanctuary researchers partner with other researchers including those at the University of Hawai‘i. These partnerships have uncovered interesting connections including a link between limu (algae) and top predators on Papahānaumokuākea's reefs with evidence that the bottom-dwelling (or 'benthic') algae serves as the base of the food web, supporting large predators (including sharks) at the top. The large predators don't eat algae directly. Rather, sharks and other large fish consume smaller herbivorous fishes, which eat algae growing on the seafloor (as opposed to microscopic planktonic algae floating in the water column).

For this study, scientists examined tissue samples smaller than the size of a pencil eraser and used carbon and nitrogen chemical signatures to determine the relative position of organisms within the food web. By analyzing nearly 600 samples of algae and fishes from Papahānaumokuākea National Marine Sanctuary, including herbivorous surgeonfishes, bottom-feeding predators such as goatfishes and wrasses, apex predators such as jacks and groupers, and several types of sharks, including 14-foot long tiger sharks, the study found that benthic algae represent nearly two-thirds of the primary productivity (the energy-producing growth at the base of the food web) in Papahānaumokuākea's reef ecosystems.

Bottom-dwelling algae such as the ones in the photos below are the base of the food web that supports top predators like tiger sharks.

Acoustic Studies of Predator Movements

To better understand the movements of top predators in the predator-dominated reefs of Papahānaumokuākea National Marine Sanctuary, researchers are using sound (acoustic) recording devices. Acoustic and satellite telemetry is used to look at movements between open-ocean and atolls, and to determine habitat use. Over 90 receivers have recorded over 300 tagged top predators. Results indicate that tiger sharks (Galecerdo cuvier) are the most wide-ranging top predator in the sanctuary, and that small top predators like ulua/giant trevally (Caranx ignobilis) or uku/green jobfish (Aprion virescens) are not moving between islands or atolls. Empirical data quantifying long-term movements and habitat use of sharks also helps researchers understand monk seal predation at Lalo (French Frigate Shoals).

Population Connectivity

University researchers have studied population connectivity of marine life among the atolls of Papahānaumokuākea National Marine Sanctuary and between Papahānaumokuākea and the inhabited Hawaiian islands. These links are important to understand whether Papahānaumokuākea serves as a source of marine larvae that produces the next generation of fish and invertebrates for the inhabited Hawaiian islands. Population connectivity can also depict whether the atolls within an archipelago are a series of isolated ecosystems that are best managed as individual units or an ecosystem connected by population reproduction and growth across all atolls. Genetic data from 27 taxa provides evidence for two barriers to gene flow among marine organisms within Papahānaumokuākea National Marine Sanctuary, one separating populations of the three northern atolls from the rest of the archipelago, and another restricting connectivity from Mokumanamana towards the inhabited Hawaiian islands.

Research partners have studied links expanding out of Papahānaumokuākea for important fisheries species. Using species-specific data collected by independent fishery observers, University of Hawai‘i scientists examined catch rates before and after the 2016 expansion of the boundaries of Papahānaumokuākea. They found evidence of spillover benefits for yellowfin (Thunnus albacares) and bigeye tuna (Thunnus obesus) supporting the value of protecting this treasured place to support and increase abundance of marine life in the surrounding marine ecosystems.

Taking A Deeper Dive

Mesophotic Coral Reefs

Mesophotic coral ecosystems are deep, low-light coral and hard-bottom habitats that typically occur from about 100 to 500 feet (30–150 meters) below the surface. Mesophotic benthic habitats, or areas of the seafloor that see little to no sunlight, are vast and complex ecosystems that serve as the foundation of food webs. These deeper reefs can also serve as extensions of shallow-water reef communities and may offer important refuge for species affected by storms, bleaching, or other disturbances. In recent decades, technological advances in diving and robotic vehicles have allowed us to explore and learn more about these diverse and important ecosystems.

Many of Papahānaumokuākea National Marine Sanctuary's mesophotic resources lie beyond the limits of conventional scuba diving techniques, so the field and research team uses specialized technologies—including mixed-gas closed-circuit rebreathers (hereafter "rebreathers") to explore and study them. With rebreathers, NOAA divers assess fish, algae, coral, and other deep-reef marine communities down to 300 feet (100 meters). Their work has revealed new algae and fish species and even a site where every recorded fish species was endemic to Hawai‘i. Partners such as the University of Hawai‘i and Bernice Pauahi Bishop Museum help to identify and catalog these discoveries.

Deep-Sea Exploration

To study the deepest marine resources in Papahānaumokuākea National Marine Sanctuary beyond the depths of scuba diving, we work with partners including NOAA Exploration, the Schmidt Ocean Institute, and Ocean Exploration Trust. These organizations provide research ships and technologies that collect bathymetric data to map the deep seafloor and use remotely operated vehicles (ROV) to study the species and ecosystem processes within these deep-sea environments. Often, they stream footage from these expeditions live, allowing viewers to virtually join scientists in exploring previously unseen deep-sea habitats.

The deep marine ecosystems of Papahānaumokuākea National Marine Sanctuary have many secrets still waiting to be found. In 2016, scientists aboard the NOAA Ship Okeanos Explorer discovered a sponge the size of a minivan in Papahānaumokuākea while using ROVs to explore some of the deepest areas of the sanctuary. This record-breaking sponge was found at 7,000 feet deep and was close to 12 feet long and 7 feet wide. It is the largest sponge known in the world to date.

Seamounts

Seamounts are underwater mountains that rise at least 3,300 feet (1,000 meters) from the surrounding seafloor, and are one of Earth's most diverse deep-sea ecosystems. These submarine mountains—most of which include the remains of extinct volcanoes—can be found in every ocean basin and serve an essential role in supporting biologically rich deep-sea ecosystems. Think of them like the underwater version of a coral reef or a kelp forest—critical foundation habitats where everything from deep-sea corals and sponges to commercially important fish and migratory species converge.

Seamounts are like 'oases' in the deep sea, serving as a gathering space for a variety of different organisms. In the cold, dark, and highly pressurized abyss of the sea, seamounts are biodiversity hotspots that are often teeming with life. As the slope of the seamount increases, deep-sea currents are forced upward, bringing nutrient-rich water that attracts a wide variety of species—from plankton to lobsters, and even sharks and whales. This productivity benefits organisms throughout the entire water column, not just in the deep sea. Corals and sponges serve as key species in the ecosystem, offering both nourishment for predators and shelter that supports a wide variety of marine life, including crabs, squat lobsters, and sea stars. The rugged terrain of seamounts creates small crevices that provide refuge for creatures like fish and octopuses.

Most seamounts are formed by underwater volcanic activity, either at "hot spots"—where molten rock rises from deep within the Earth—or along the edges of tectonic plates. Seamounts can form in other ways too, but these are the most common. In Papahānaumokuākea National Marine Sanctuary, the Liliʻuokalani Ridge Seamounts formed through hotspot volcanism and tectonic plate movement. This seamount chain was created during the mid to late Cretaceous period, between about 143 and 66 million years ago. At that time, the Pacific Plate was moving more to the north than it is today—a shift that can be seen in the angle of the Liliʻuokalani Ridge compared to the Hawaiian Ridge. By studying these seamounts and the clues they leave on the seafloor, scientists gain insight into Earth's dynamic geological processes over millions of years.

We are still learning so much about the world around us, and seamounts are full of interesting discoveries. Because seamounts lie deep beneath the ocean's surface, scientists rely on advanced technology to explore them. At NOAA, we use a range of underwater robots to study these towering underwater mountains. One type is autonomous underwater vehicles (AUVs), which are pre-programmed to follow a path while collecting valuable data using onboard sensors and cameras. Another key tool is remotely operated vehicles (ROVs), which are connected to a ship via long cables and piloted from the surface. ROVs can be outfitted with video cameras, lights, sensors, robotic arms, and collection chambers to gather deep-sea samples.

Seamounts might be out of sight, but their impact reaches your dinner plate, your medicine cabinet, and your local economy. Seamounts serve an essential role in a thriving ocean and support a range of organisms—from commercially-important tuna populations that fishermen rely on, to migratory whales and birds that eco-tourism businesses rely on.

According to the International Union for the Conservation of Nature, roughly 200,000 seamounts exist throughout the world, and over 30,000 seamounts are known to exist in the Pacific Ocean alone, but less than 300 of the world's seamounts have been explored and relatively few are protected. NOAA's Office of National Marine Sanctuaries researches and monitors seamounts within the boundaries of America's protected underwater parks by studying their geological history and their complex deep-sea ecosystems in order to increase our understanding of the role that these underwater mountains play in the greater marine environment.

The National Marine Sanctuaries Act enables research on seamounts by protecting these unique deep-sea features within sanctuary boundaries and supporting the tools needed to explore them—like remotely operated vehicles, underwater mapping, and imaging technologies. By fostering collaboration among scientists, universities, Indigenous communities, and other partners, sanctuaries serve as living laboratories where researchers have the tools and access necessary to study seamount geology, biodiversity, and ecosystem function, and share their findings with the public.

The seamounts found within the waters of national marine sanctuaries, such as at Monterey Bay, Papahānaumokuākea, and American Samoa offer excellent opportunities for continued exploration and discovery, and are safeguarded for years to come.

The Intertidal Zone

One of the most dynamic marine environments is the intertidal zone. Here marine critters regularly experience an air environment during low tide, followed by a submerged aquatic environment during high tide. Intertidal marine organisms must survive a complete shift in temperature, light intensity, access to oxygen, and exposure to both land and sea predators. The intertidal zone is also one of the primary marine ecosystems that land dwelling organisms, like humans, interact with.

Intertidal Monitoring

Intertidal monitoring expeditions are conducted within Papahānaumokuākea National Marine Sanctuary to assess and better understand the shorelines and shallow water ecosystems of high islands within the sanctuary (e.g., Nihoa, Mokumanamana, La Perouse Pinnacle at Lalo (French Frigate Shoals), and ʻOnunui and ʻOnuiki (Gardner Pinnacles)). These expeditions integrate cultural knowledge and practices with western science and provide managers with insights into how to make better informed decisions concerning the harvest of intertidal species in the inhabited Hawaiian Islands.

‘Opihi (Hawaiian limpet) are the primary research focus of intertidal monitoring surveys, where scientists are investigating patterns in habitat use and reproduction of different ‘opihi species in different subsections of the intertidal habitat in Papahānaumokuākea. ‘Opihi is a Hawaiian delicacy and culturally important species whose numbers have been dwindling in the inhabited Hawaiian Islands due to overharvesting. This research aims to inform sustainable harvest protocols

These expeditions include Office of National Marine Sanctuaries staff, University of Hawai‘i researchers, cultural practitioners, as well as representatives from Native Hawaiian Organizations who are involved in sustainably managing ‘opihi stocks. Field teams also monitor other intertidal organisms including the limu (algae) along the rocky shoreline habitats. These expeditions incorporate huli‘ia, a method to collect detailed, holistic observations based on indigenous knowledge systems that build intimate knowledge of the surrounding environment.

The creation of seasonal calendars is one product born from Huli‘ia where connections are drawn between dominant patterns in the atmosphere, land, and ocean. It is a collaborative effort to strengthen place-based knowledge and re-establish healthy relationships between people and place.