Marine Habitats and Ecosystems

A significant part of the Center's research is directed at surveying, monitoring, modeling and assessing marine habitats and ecosystems in U.S. waters and open oceanic waters of the central and western Pacific. Studies range from surveys of coral reefs and pelagic habitats using NOAA vessels to complex modeling of ocean properties and impacts of climate change. During 2011, progress was noted in several areas:

Study of Ocean Circulation Advances Understanding of Marine Debris Concentrations in North Pacific

Ocean currents drive large-scale circulation in the North Pacific, creating a pair of major gyres joined by a transition zone. At 
                   the southern edge of the transition zone, areas of convergence are formed where marine debris accumulates. Two areas of 
                   significant debris concentration are known as the Eastern Garbage Patch (EGP) and the Western Garbage Patch (WGP).
Ocean currents drive large-scale circulation in the North Pacific, creating a pair of major gyres joined by a transition zone. At the southern edge of the transition zone, areas of convergence are formed where marine debris accumulates. Two areas of significant debris concentration are known as the Eastern Garbage Patch (EGP) and the Western Garbage Patch (WGP).
Debris washed into the sea by the massive March 11, 2011 tsunami in northeastern Japan was initially highly concentrated. Over 
                   time, it will disperse widely across the North Pacific Transition Zone and circulate in the Subtropical Gyre in a pattern 
                   dictated by ocean currents. Photo courtesy of U.S. Navy Pacific Fleet.
Debris washed into the sea by the massive March 11, 2011 tsunami in northeastern Japan was initially highly concentrated. Over time, it will disperse widely across the North Pacific Transition Zone and circulate in the Subtropical Gyre in a pattern dictated by ocean currents. Photo courtesy of U.S. Navy Pacific Fleet.

The term "garbage patch" has become familiar to many people thanks to media coverage of marine debris and its effects on ocean habitats and ecosystems. Public awareness of the issue was greatly heightened by the Tōhoku earthquake that struck northeastern Japan in March 2011, and the resulting tsunami that devastated coastal communities. The tsunami injected an enormous amount of debris into the North Pacific. The fate of that debris is of particular interest to mariners, scientists, and conservationists. Scientists have used computer simulation models to predict the spread of the tsunami debris. The accuracy of predictions depends on how well the models take into account factors that affect debris longevity, dispersal and distribution, such as circulation patterns and effects of climate variability.

A team of PIFSC scientists and other NOAA researchers published a timely review of information on the key determinants of marine debris concentration in the North Pacific. Their 2011 research article, appearing in the peer-reviewed journal Marine Pollution Bulletin [1], provides key information on factors that affect the distribution of the tsunami-generated debris.

The team began their article by reviewing the primary oceanographic features and climatology of the North Pacific, including the large-scale circulation associated with the Subpolar Gyre, the more southerly Subtropical Gyre, and the Transition Zone between the two major gyres [see schematic of ocean currents]. Then they focused on the Subtropical Gyre and Transition Zone. The clockwise-rotating Subtropical Gyre is the largest circulation feature on earth and is home to the globe's largest contiguous biome. The Transition Zone is bounded north and south by various frontal systems important as foraging habitat for pelagic biota including albacore tuna, swordfish, sea turtles and seabirds.

The authors reviewed information on the convergence zones created by the large-scale circulation pattern; these are places where marine debris tends to accumulate and/or be retained. In particular, they described three key areas of debris accumulation: the broad Subtropical Convergence Zone along the southern edge of the Transition Zone and "garbage patches" at the eastern and western extremities of this zone. The latitudinal position of the Subtropical Convergence Zone changes seasonally, occurring farther north during the summer and shifting southward in the winter. In some winters, the Subtropical Convergence Zone and associated frontal systems drop down into the northernmost part of the Hawaiian Archipelago with significant consequences for the local ecosystem. Primary production in the fronts may enhance biological productivity in waters surrounding the affected islands and atolls. Moreover, the convergent fronts transport accumulations of derelict fishing gear and other marine debris into the coral reef habitats where it poses a risk to endangered Hawaiian monk seals and other fauna. At the eastern end of the Subtropical Convergence Zone, marine debris accumulates in the famous "Great Pacific Garbage Patch". And at the western end, in waters south of the Kuroshio Extension, debris is concentrated in the lesser-known "Western Garbage Patch".

In the final part of journal article, the team described key climate drivers of variability in marine debris concentrations. In particular, they noted that interannual fluctuations in Subtropical Gyre circulation are affected by the El Niño-Southern Oscillation and larger-scale patterns are influenced by the Pacific Decadal Oscillation and North Pacific Gyre Oscillation. In anticipation of the landfall of marine debris from the Tōhoku tsunami, NOAA and its federal and non-federal partners have launched plans to monitor the debris at sea and ashore and assess and mitigate its effects on sensitive marine ecosystems.

Ecosystem Model Describes Complex Linkages in Nearshore Habitat of Hawaiian Green Sea Turtles

One of the encouraging stories in conservation biology has been the marked resurgence of green sea turtles in the Hawaiian Islands, spurred by a ban on harvesting since the 1970s. Counts of nesting female green sea turtles at East Island, a key breeding site in the Northwestern Hawaiian Islands, have increased 3-fold since monitoring began 39 years ago. The abundance of green sea turtles has also increased noticeably in nearshore waters and coral reefs around the islands, where the turtles settle and reside as juveniles and adults after an early post-natal stint in the open ocean. To learn about the green sea turtle population, PIFSC scientists regularly monitor resident turtles at several coastal study sites, including one at Kaloko-Honokōhau National Historical Park (Kaloko) on the island of Hawaii. Monitoring data at Kaloko and several other sites have shown that growth rate and body condition of the turtles have diminished as turtle numbers have increased. To scientists, this suggested that the abundance of turtles at these sites may have reached the local "carrying capacity", the maximum number of turtles the habitat is able to support.

Feeding interactions between organisms in the Kaloko reef ecosystem are complex and varied. Foraging green sea turtles, 
                   herbivorous fishes, and sea urchins compete with each other for turf algae and other plant life.
Feeding interactions between organisms in the Kaloko reef ecosystem are complex and varied. Foraging green sea turtles, herbivorous fishes, and sea urchins compete with each other for turf algae and other plant life.

To better understand the situation at Kaloko, a team of researchers led by a scientist from the University of British Columbia considered not just the turtles, but the entire coral reef ecosystem of which turtles are just one component. They developed a quantitative model of the ecosystem that included 26 groups of organisms at Kaloko: corals, phytoplankton, planktivorous fishes, algae of various kinds, invertebrate species like sea urchins and crabs, herbivorous fishes, corallivorous fishes, piscivorous fishes, sea turtles, seabirds, Hawaiian monk seals, spinner dolphins, and more. Information on fishing within Koloko, though meager, was also compiled and included in the analysis. Using a powerful modeling tool called Ecopath/Ecosim, the research team synthesized biological data for each of group of organisms for the year 2005. Then they used the model to describe the complex structure of the ecosystem, including interactions and dependencies between the various components. Along with the green turtle, primary interest was focused on the populations of algae that are the turtle's food base and the herbivorous fishes and urchins that directly compete with green sea turtles for that forage. The model allowed the research team to estimate the abundance, consumption and productivity of each component. Herbivores accounted for 43% of all living biomass in the ecosystem with 93% of that contributed by sea urchins. Moreover, the analysis showed very high levels of "ecotrophic efficiency" for macroalgae and turf algae; that is, almost all the production by these plant groups was consumed by the plant-eating fauna of the ecosystem—the herbivorous fishes, urchins, and green turtles. Thus, in the aggregate, herbivores are at their carrying capacity within the system and exert strong competition with one another for algal resources. And green sea turtles specifically, which appear to graze mostly on turf algae growing on the nearshore lava bench at Kaloko, are at carrying capacity. This explains why the turtles are leaner and growing slower than they were in early surveys.

Shoreline developments are projected around the Kaloko-Honokōhau National Historical Park that will likely affect the coral reef ecosystem To the extent such developments cause greater enrichment of the reef by terrestrial runoff or greater fishing pressure on herbivorous fishes, the ecosystem, particularly the algal and herbivore components, will be altered. The ecosystem model gives scientists a powerful tool for evaluating such impacts. It is important that the model includes the Hawaiian green sea turtle, as its efficiency in cropping algal resources adds to the reef's resiliency.

The Kaloko study was published in the peer-reviewed journal Marine Ecology Progress Series [2].

Surveys Document Inshore Fish Community at Remote Pacific Islands

Pelagic barracuda are part of the coral reef fish community in the Line Islands.
Pelagic barracuda are part of the coral reef fish community in the Line Islands.

In a series of surveys from 2000-2008, PIFSC researchers and collaborating scientists expanded our understanding of the shoreline fish fauna at several U.S. atolls in the equatorial central Pacific: Howland Island and Baker Island of the Phoenix Island group, and Jarvis Island, Palmyra Atoll and Kingman Reef of the Line Island group. Together these atolls and their surrounding waters comprise the Pacific Remote Islands Marine National Monument. Because this region is so isolated and seldom visited, relatively little is known of its biotic community and the oceanographic factors shaping its makeup. Prior to the recent surveys, a scant ichthyological record had been compiled from infrequent scientific expeditions to the region, beginning in 1864.

The PIFSC surveys were part of a comprehensive effort by the Center's Coral Reef Ecosystem Division to document and assess the biodiversity of coral reefs across the U.S. Pacific islands, including remote, uninhabited atolls and areas with populated islands like American Samoa, Commonwealth of the Northern Mariana Islands, Guam and Hawaii. During multifaceted expeditions to monitor and assess the coral reefs, teams of scuba divers were deployed during daylight to systematically identify and count non-cryptic, reef-associated fish between 3 and 20 m depth. Various survey protocols were used: free-swimming along designated transects, towed-diver surveys, rapid ecological assessment surveys, and stationary point counts. Detailed lists of identified fish species and animals higher in the food web were compiled for each island. Identifications were based mostly on visual assessment; few were substantiated by photos or voucher specimens. A variety of statistical methods were used to estimate biogeographic characteristics of fish counts at the 5 surveyed islands and compare them with those at other Pacific islands and archipelagos.

The surveys recorded 506 species of reef-associated shore-fish. A high percentage of records represented the first documented sightings of the species at these islands: 50.8% of the 328 species observed at Howland, 70.1% of the 268 species at Baker; 64.2% of the 274 species at Jarvis, 28.6% of the 395 species at Palmyra; and 78.5% of the 270 species at Kingman. Most species known to occur in the Line and Phoenix Islands but not recorded in the surveys were cryptic species; for example, nocturnal species not apt to be seen in the diurnal surveys.

Sixty-nine percent of the fish species encountered have broad distributions across the Indo-Pacific, many ranging from east Africa to French Polynesia. Others have narrower distributions in the western Pacific; some are endemic to the region. The research team found that the 5 surveyed islands are unique among U.S. possessions in having reef fish species not seen in other U.S. waters. Some of these species are members of the endemic central Pacific fauna about which we know little. These islands are among the least-studied places on the planet. Not only are the fish communities poorly understood, but so are the oceanographic processes that influence biogeographic patterns in the species distributions and abundance. Further study of these remote U.S. atolls will advance knowledge of the ecology, biodiversity and evolution of the region's fish fauna.

The study was published in the peer-reviewed journal Atoll Research Bulletin [3].

Grey reef sharks were routinely observed at each of the five remote U.S. Pacific islands surveyed.
Grey reef sharks were routinely observed at each of the five remote U.S. Pacific islands surveyed.