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NOAA: Overall biological diversity is high in Nat’l Marine Sanctuary

Fogamaa coral assemblage
However there is concern over some fish and coral species

Pago Pago, AMERICAN SAMOA — In this second part of Samoa News coverage of the condition of the National Marine Sanctuary of American Samoa (NMSAS) released by National Oceanic and Atmospheric Administration (NOAA) since it was expanded a decade ago we will look at the overall biodiversity.

The NMSAS condition report records great concern over the scarcity of large fish — sharks, parrotfish, surgeonfish, and unicornfish, which are all important components of coral reef ecosystems.

Whitetip, gray reef, blacktip, and nurse sharks are the most common reef sharks encountered in American Samoa; however, surveys have recorded very low shark densities in American Samoa compared to some other islands in the South Pacific.

“Large parrotfish, through their diverse feeding strategies, play an important role in coral reef ecosystem dynamics by removing algae, opening up substrate for coral settlement, and keeping fast-growing coral species in check. Surgeonfish and unicornfish are also important, filling a number of functional roles as grazers, browsers, detritivores, and planktivores.”

“Sharks are at 4- 8% of their potential biomass, bumphead parrotfish are now functionally extinct, abundances of other large parrotfish species remain low, and low biomass estimates may indicate unsustainable fishing pressure.

“The continued lack of large predators and large herbivores in shallow coral reef habitats is a major concern, as this may compromise ecosystem resilience.

In the report, NOAA cited that living resources within the sanctuary have not been fully documented, but are best characterized in shallow coral reef ecosystems.

“Coral reefs are diverse, complex systems, and many species are highly specialized, making it difficult to identify keystone species.

“In the sanctuary’s mesophotic and deep-sea ecosystems, too little is known about ecological interactions and individual species’ roles in the ecosystem.

 [Mesophotic coral ecosystems are found in tropical and subtropical regions at depths ranging from almost 100 feet to over 490 feet below the ocean's surface.]

“Therefore, groups of ecologically important species were evaluated for their combined contributions to the ecological integrity of their respective ecosystems. Keystone and foundation species groupings include zooxanthellate scleractinian corals, crustose coralline algae, reef sharks, large parrotfish, surgeonfish and unicornfish, mesophotic corals, and deep-sea corals and sponges.”

Furthermore, stony (scleractinian) corals are important foundation species for shallow coral reef ecosystems, providing structure and food for many other reef organisms.

“Over 150 species of coral have been documented in the sanctuary, but species-specific data are limited. Scleractinian corals in the sanctuary are robust and include healthy populations of both large, old corals and recruits. Although repeated bleaching has affected these communities, particularly at Swains Island, they remain resilient.

“Crustose coralline algae are an important component of the reef in American Samoa, cementing the reef substrate together, stabilizing rubble after disturbances, building algal ridges along high-energy reef margins, creating habitat for fish and invertebrates, and attracting coral larvae to settle on reefs. Crustose coralline algae cover in the sanctuary remains high and has even increased at many sites.

“Approximately 110 species of scleractinian corals are found at mesophotic depths in American Samoa, and corals and sponges provide important habitat for echinoderms and other organisms in the deep-sea habitats.

“Although there are limited monitoring data for mesophotic coral ecosystems and deep-sea corals and sponges, available information suggests that these species are in good condition. However, limited data in these areas do suggest that recruitment is low for deep-sea coral species.”

Other focal species found in the sanctuary include giant Porites corals, giant clams, humphead wrasse, sea turtles, and humpback whales.

“The abundance of harvested species, including giant clams, targeted food fish species, and humphead wrasse, is low and recovery is uncertain due to continued harvesting and life cycle characteristics.

“The decline in giant clams from 1996 to 2006 is particularly worrisome to resource managers, and there is some concern that ocean acidification and elevated seawater temperatures may be affecting these species.

“Data on sea turtles suggest that resident populations may be slowly recovering, but nesting activity is still limited. Humpback whale populations may also be increasing, but data are limited, and increasing ocean temperatures may shift the preferred habitat for this species away from American Samoa.

“More specific survey efforts for giant clams, humphead wrasse, and rare food fish species, as well as expanded survey efforts for sea turtles and humpback whales, are recommended.

“Non-indigenous species have been observed in American Samoa, but have not exhibited invasive characteristics within sanctuary units. A tunicate and a green alga have recently exhibited invasive behavior, but are believed to be native species. No recent surveys have been conducted specifically to look for invasive species, and this is an important biosecurity gap that needs to be addressed.

“Overall, biological diversity is high in NMSAS, but needs to be further explored, as additional species continue to be documented and new species have been recently discovered.

“Recent mesophotic and deep-sea expeditions have expanded the list of known species within the sanctuary, and further study is likely to expand this list further.