Ocean Exploration and Scientific Discovery in the Marianas from 2016 to 2021

This document was prepared for the Friends of the Mariana Trench in support of the five year review of our proposed national marine sanctuary in the Mariana Islands. The waters surrounding the Mariana Islands contain natural resources and ecological qualities of national significance, and this document compiles ongoing exploration, research, and discovery that has taken place since 2016. The information contained in this document strengthens the case to keep the proposed national marine sanctuary in the inventory list, and to move forward with the designation process without delay.

The Friends of the Mariana Trench thank Ahmyia Cacapit of Guam for drafting this report, and Dr. Stephen Mana’oakamai Johnson and Mr. Angelo Villagomez of Saipan for reviewing it.

A Sanctuary for Endangered Humpback Whales
  • 14 Species of whales have been recorded by scientists in recent years, but there is evidence of more
  • Fin and blue whales, the two largest whale species in the world, have been recorded acoustically
  • Individual humpback whales documented in the Marianas have been seen in Russia, Japan, and the Philippines
  • The Marianas may serve as a refuge for humpback whales, paralleling the Hawaiian Islands Humpback National Sanctuary

There have been limited studies of cetaceans in the Marianas compared to other regions around the world. However, anecdotal observations such as sightings and strandings suggest that the Marianas provide habitat actively used by these animals. Local populations of marine mammals provide ecological functions in their habitat and can bolster environmental awareness for the islands’ community.

Small-scale surveys conducted by the Pacific Islands Fisheries Science Center from 2010 to 2019 allowed researchers to determine what species of cetaceans are present in the Marianas. Currently, fourteen species have been visually observed throughout the Marianas archipelago including: humpback whale, sperm whale, false killer whale, spinner dolphin, bottlenose dolphin, among others (Hill et. al, 2020). Acoustic recordings of minke, fin, and blue whales have also been documented in the area (Hill & Yano, 2021).

Photo-identification showed that individual humpback whales in Saipan were later observed in Russia, Japan, and Philippines, suggesting that the island may serve as a crucial area for migrating populations (Hill et. al, 2020). A complex whale call was observed near the Marianas Trench Marine National Monument, highlighting the potential to track revisits of these animals around the waters to understand habitat usage of our region (Nieukirk et. al, 2016). These notable observations have encouraged further exploration into these specific humpback populations.

In 2020, NOAA researchers determined that Saipan served as a breeding ground for endangered humpback whales after observing multiple mother-calf pairs. These recordings implied that young calves were born in surrounding waters; however, geographic limitations of the habitat off the western coast of the island is still unknown (Hill et. al, 2020). Future studies will likely track humpback numbers throughout the entirety of the archipelago to determine the extent of this usage site.

Because humpback whales are listed as endangered by the US Endangered Species Act, the US Exclusive Economic Zone around the Mariana Islands should be considered as essential habitat for population recovery and further assessment for these existing populations. The Marianas may serve as a refuge, paralleling the Hawaiian Islands Humpback National Sanctuary, a protected area which is recognized under IUCN category IV classification.

Currently, the Hawaiian Islands Humpback Whale Sanctuary is the only successful site in accordance with their criteria of legal documentation of their goals, long-term monitoring, and management (Cook et. al, 2019). Similar to Hawaii, establishing a humpback whale sanctuary in the Marianas can serve as the intersection for researchers, management, and stakeholders regarding whales in the region.

Keeping the proposed national marine sanctuary in the inventory list and moving forward with designation will improve the capacity of the Mariana Islands to study and protect these iconic species.

Coral Reef Ecosystem Monitoring and Resilience
  • Coral reefs are culturally and economically important ecosystems in the Mariana Islands
  • Research in the Marianas archipelago is contributing to our understanding of the effects of climate change on coral reefs.
  • Healthy coral reefs will be a multi-million dollar attraction for overseas tourists once the economic recovery from the Covid-19 pandemic begins
Coral reefs are important ecosystems that support people and marine life in the Marianas. The complex structure of coral reefs support fish by providing shelter, protection, food, and nursery sites. Reefs also absorb wave energy and protect coastal environments. Importantly, coral reefs play an integral role to the Indigenous community by promoting traditional fishing practices and environmental awareness. There are over 400 species of corals identified in the Marianas, the highest coral diversity in United States waters (Waddell, 2005). Currently, corals within the Marianas face a variety of threats from global climate stressors such as rising sea surface temperatures and ocean acidification, to local threats such as fishing, pollution, and runoff.

Recent work throughout the Marianas has helped understand how coral reefs are being impacted by both climate change and local stressors. In the past decade, the region has faced elevated sea surface temperatures, resulting in subsequent bleaching events from 2013 to 2017. These bleaching events resulted in major loss of coral due to the breakdown of the symbiosis between corals and their photosynthetic algae. In Guam, coral cover declined by 36% by 2017. Fast-growing branching corals in the region faced the most loss while slow-growing corals persisted better, showing potential resilience for certain groups (Raymundo et. al, 2017).

Starting in 2013 after a major bleaching, NOAA researchers and local government managers began to shift focus from high priority areas to shallow reef communities after observing stronger effects from environmental stress (Burdick et. al, 2019) . Since then, Guam has faced subsequent bleaching events in 2014, 2016, and 2017.

Further research has investigated the status of reefs in isolated islands in the Marianas Archipelago. One study showed that corals on the uninhabited island of Farollon de Medinilla were also threatened by the bleaching event. The impacts paralleled the findings in Guam, with massive corals showing higher tolerance for thermal stress (Carilli et. al, 2020). In another study, researchers examined the effects of ocean acidification on the coral reefs in Maug, where the island receives CO2 enrichment from volcanic activity. A shift from hard coral to macroalgae dominance was observed with declining pH (Enochs et. al, 2015). This study highlighted important transformations that coral reef ecosystems globally may undergo as global ocean pH levels are projected to reach Maug’s by the end of this century.

Resiliency after mass bleaching events were studied along with ways to mitigate other environmental stressors. Three sites in Guam were identified with high resilience as well as five sites with medium-high resilience. These locations showed fastest recovery rates and demonstrated the influence of algal cover on coral reef health (Maynard et. al, 2018).

Researchers also identified ways that land management can promote coral health following stress events. They found that watershed restoration adjacent to reefs decreased sedimentation and resulted in less oxidative stress (Lindfield et. al, 2016). These efforts informed management on proactive steps these island communities could take to aid in reef recovery.

Fish and wildlife within these coral reef ecosystems have also been examined to understand how they are being impacted from natural threats and fishing pressures (Houk et. al, 2014). Unicornfish (Naso) and rabbitfish (Siganus) have been more resilient, while other species have declined due to fishing pressure (Houk et. al, 2018; Wolanski et. al, 2020). In addition, the Endangered humphead wrasse was documented in Saipan. Researchers successfully mapped out their distribution despite its elusiveness and identified key habitat associations for the rare species (Trianni et. al, 2021). All three studies focused on culturally significant species that are prominent in the local diet and indigenous history.

In Guam, coral reefs are valued at $127 million per year while Saipan’s coral reefs are estimated at $61.2 million per year through various contributions to the community such as tourism, fishing, diving, and cultural practices (van Beukering et. al, 2007; Conservation International, 2008). The highest contribution that coral reefs make is to the tourism industry in the Marianas, attracting foreign visitors across Asia. During the COVID-19 pandemic, tourism was halted throughout the region which greatly impacted revenue for the islands. As these economies recover, coral reefs provide substantial incentive for future visitors through activities and aesthetics.

Keeping the proposed national marine sanctuary in the inventory list and moving forward with designation will support the Marianas in understanding climate and other anthropogenic threats to coral reefs and will support the protection and management of these critical habitats.

Home to Wondering Turtles and Whale Sharks
  • With increased protections, the Marianas could be a potential recovery site for populations of green and hawksbill turtles
  • Hatchlings born in the Marianas remain in our waters for 17 to 24 years before they begin migrating
  • The waters around the Marianas are a highway for migrating species, including whale sharks that swim across the Pacific Ocean from Panama
Many marine species identified in the Marianas are listed under conservation concern and/or have protected status; however, there is limited information on population data to understand how their numbers are changing as time progresses. A primary example of this can be seen in sea turtles, where overall populations are declining but regional data to determine growth or decline is low. Population size and distribution is limited for the Endangered green sea turtle and the Critically Endangered hawksbill turtle throughout the western Pacific. Locally in the Marianas, turtles are harvested for meat and jewelry, but these practices have been banned since 1981 (CNMI Public Law 02-51, 1981). Previously in the archipelago, turtles were harvested for meat and jewelry, but protection under the Endangered Species Act of Guam gave turtles full protection and prohibited any takes by humans. Despite these regulations, illegal activity such as poaching still occurs today. As these islands face both environmental and anthropogenic pressures, researchers found it necessary to learn baseline data that support conservation efforts and local fisheries.

Scientists found that the CNMI may serve as a potential recovery site for growing populations of sea turtles with increased protection and management efforts. A recent NOAA study investigated the diet and size of marine turtles in the CNMI to gain more information about resident turtles. Scientists found that turtles may reside in the region for an average of 17 years and may remain up to 24 years (Summers et. al, 2017). NOAA researchers also found that turtles in the CNMI had high nest abundance (Summers et. al, 2017). During this study, increased warming also increased embryonic death and current poaching also posed a threat. For hatchlings that did survive, scientists noticed higher rates of female offspring. Because sex is determined by nest temperatures, future generations may be unbalanced with lower male numbers. Future studies and actions may encourage higher protection and monitoring for male turtles.

Whale sharks, sea turtles, and other highly migratory species will benefit from the designation of the proposed national marine sanctuary through improved research, outreach, and education of the need to protect and manage these iconic species.

Mariana Trench Discoveries and Environmental Awareness

  • Exploration of the Mariana Trench is ongoing, with new discoveries taking place as researchers investigate one of the ocean’s most elusive regions
  • Exploration and research in the Mariana Trench show evidence of human activities
The Mariana Trench is one of the most unexplored habitats in the world. It is the deepest trench in the world containing an array of different ecosystems including underwater volcanoes, abyssal plains, and hydrothermal vents. These mysterious habitats allow researchers to learn about unique processes that involve adaptation to extreme conditions. Scientists can also uncover human impacts in one of the most exclusive parts of the ocean.

NOAA conducted an expedition on the Okeanos Explorer in 2016 to obtain baseline data for unknown and poorly documented regions surrounding the trench (Diva et. al, 2020). During their cruise, hundreds of different species were observed through remote-operated vehicles.

Additionally, various researchers have discovered new species of different animal groups in hydrothermal vents, ecosystems where seawater is heated within the earth’s crust and then released. This type of habitat was discovered in 1977 and is an emerging field of study to uncover information about the deep ocean. The first Cuspidaria bivalve was found at a deep-ocean hydrothermal vent (Chen et. al, 2018) while new species of Alvinocaris and Rimicaris shrimp were also revealed (Hiraoka et. al, 2019, Giguere 2020). Other new species were described in the Mariana Trench including the amphipod Eurythenes plasticus (Weston et. al, 2020).

In 2020, Chinese explorers on the Fendouzhe reached the deepest part of the Mariana Trench. The expedition accomplished one of the deepest manned-dives in the Challenger Deep, the deepest part of the trench. This cruise set a national record for China, reaching 10,909 meters, and contributed to the country’s new mission for exploring deep sea resources (Westcott, 2020). In 2021, Nicole Yamese became the first Micronesian and the second-youngest person to reach the Challenger Deep (Letman, 2021). She was nominated by the Micronesia Conservation Trust to accompany Victor Vescovo, a deep sea explorer, on his mission to map out the seafloor in the trench.

Human impacts were also observed in the Mariana Trench. Microplastics, small plastic debris that has broken down from bigger products, were observed in the deepest part of the ocean. Researchers found that microplastic sundance was higher in the trench than in open ocean waters and sediments, with concentrations ranging from 200-22.000 pieces per liter (Peng et. al, 2018).

In addition to plastic debris, researchers also found that mercury, also originating from human pollution, is transported down after being absorbed from animals on the surface. These organisms sank to deep depths where they were consumed by amphipods and snailfish in the trench (Krishnamoorthy, 2021).

Furthermore, researchers created a global database for the compilation of deep-sea plastic debris over a 30-year span. Through these surveys, they found that a plastic bag was recorded in the Mariana Trench, with a depth of 10,898 m (Chiba et. al, 2018). These discoveries illustrate that the Mariana Trench may serve as a large sink for microplastics and that manmade pollution reaches even the most secluded parts of the ocean.

However, the most exciting thing about the Mariana Trench and the surrounding region is not that which was discovered recently, but that which has yet to be discovered. The region is understudied, but is geographically diverse and near to global hotspots of biodiversity. Isolated and unexplored ocean depths, seamounts, and near shore island ecosystems are likely teaming with endemic plants and animals, yet undiscovered by science. The offshore region has been mostly unfished for 40 years and is one of the last remaining wildernesses in the United States. This area is nationally and globally significant from a biological and geological perspective, and when you consider the 4,000 year history and unique cultures of the Chamorro and Refalwash people on the islands, it is clear that the proposed national marine sanctuary meets the criteria for inclusion in the inventory list and ultimately designation.


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