Thursday, November 12, 2026

Scientists find some of the ‘very last wild and healthy ecosystems’ in the world’s oceans untouched by humans

Remote atolls in the Pacific Ocean teem with life across habitats and may serve as reference to what has been lost elsewhere

Frontiers

Schools of fish at the National Marine Sanctuaries of Bikar and Bokak — video:
Schools of Grey Reef Sharks (*Carcharhinus amblyrhynchos*) and Rainbow Runners (*Elagatis bipinnulata*), along with several Red Snappers (*Lutjanus bohar*), Blacktip Reef Sharks (*Carcharhinus melanopterus*), and Black Jacks (*Caranx lugubris*) at Baited Remote Underwater Video Station.
To receive the file in a higher resolution, please write to press@frontiersin.org.
view more
Credit: National Geographic Pristine Seas.

Humans have left their mark on virtually every place on the planet, from the deep sea to the peaks of the highest mountains. But a few very remote atolls in the Pacific Ocean may be exceptions. A new Frontiers in Marine Science study has found two coral atolls, Bikar and Bokak, located on the territory of the Marshall Islands, to be some of the most intact ecosystems remaining in the region and perhaps the world.

“This study provides the first comprehensive ecological baseline of the newly created National Marine Sanctuaries of Bikar and Bokak atolls from the sky and land to the deep sea, and highlights some of the most intact ecosystems remaining in the region,” said first author Dr Alan Friedlander, a marine ecologist at the University of Hawai’i, who served as Pristine Seas’ chief scientists aboard the joint expedition. “Bikar and Bokak are not just treasures for the Marshall Islands but for the entire planet, a gift from the community of Utirik Atoll, which has traditionally and vigilantly safeguarded these fragile ecosystems for decades.”

Looking towards the future

Bikar and Bokak are the northernmost atolls in the Marshall Islands, lying approximately 116 and 385 kilometers from the nearest inhabited atoll, respectively. In 2023, the team conducted extensive monitoring of local land, sea, and sky ecosystems. They assessed sea- and shorebird populations, characterized vegetation, and carried out surveys of turtle nesting, coral reefs and fish assemblages using scuba, underwater video, deep-sea camera deployments, and a submarine.

“We set out to inform the creation of a highly protected area within the scope of the Marshall Islands’ Reimaanlok vision, which means ‘looking towards the future,’” said Friedlander. “It is a national, community-led conservation framework designed to protect marine and terrestrial resources while ensuring island life thrives for generations to come.”

Two years after the assessment, some 48,000 square kilometers around the atolls were declared the country’s first national marine sanctuary.

Teeming with life

“These atolls have extensive seabird colonies, mature native vegetation, active turtle nesting, high reef-fish biomass and large predators, coral-dominated reefs at Bokak, structurally complex mesophotic habitats, and surprisingly diverse and poorly known deep-sea communities,” said Friedlander.

Across both atolls, the researchers found 15 seabird colonies that were confirmed or likely to be breeding. They also found at least 266 groups of reef fish, 138 groups of fish living at greater depths, and 79 groups of deep-sea fishes. 15 groups of open-water predators including sharks, jacks, and wahoo, were recorded. 14 of the observed groups haven’t previously been recorded in the Marshall Islands, and two might be species new to science.

Despite sharing many characteristics and housing many of the same species, the atolls also differ from each other. Sea turtle nesting, for example, was almost exclusively concentrated at Bikar, with 132 green sea turtle nest pits recorded. The total biomass of reef fish was higher at Bokak which is characterized by coral-dominated reef communities. Bikar, on the other hand, supported more taxa of algae.

The study, which surveyed the atolls at one point in time, did not determine the environmental mechanisms causing differing ecological patterns. They could be attributed to difference in lagoon size, water exchange, sediment transport, habitat configuration, nutrient dynamics, or ecological history, among other things.

“There is also a bit of a lottery involved as to which species show up and persist at remote locations,” Friedlander added.

What we stand to lose

The extensive surveying of these ecosystems offers an unparalleled glimpse into how they function with only minimal human influence.

“They are among the best ecological reference systems we have to better understand what we have lost elsewhere and to provide fundamental insights needed for effective conservation and restoration efforts,” said Friedlander.

The important lesson, the researchers said, is that monitoring should not focus exclusively on shallow reefs but assess ecosystems in their full complexity, which provides a more complete foundation for conserving ecosystem integrity and tracking future climate-driven change. Future studies should also focus on examining nutrient transfer and ecological connectivity between habitats, which was not done here.

“The Marshall Island government should be applauded for their foresight in protecting these global biodiversity hotspots, where human activity is distant and habitats teem with life,” concluded Friedlander. “As human activities increasingly threaten biodiversity, areas devoid of intense human impacts serve as vital refugia. Large marine protected areas serve as globally important ecological reference systems for understanding the structure and future trajectories of tropical oceanic ecosystems in the Anthropocene.”

Journal

Frontiers in Marine Science

DOI

10.3389/fmars.2026.1957660

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

From the sky to the deep sea: ecosystem structure and ecological integrity across the National Marine Sanctuaries of Bikar and Bokak, Marshall Islands

Article Publication Date

11-Nov-2026

Bumphead parrotfish at Bokak atoll.

Forereef habitat at Bikar.
Green sea turtle hatching at Bikar.
Credit
Manu San Félix

Brown bobbies at Bikar atoll.
Credit
Chris Thompson.

Giant clams at Bokak atoll
Credit
Alan Friedlander.
**Grey Reef Sharks at National Marine Sanctuaries of Bikar and Bokak [VIDEO]**

Nemo’s priorities: Clownfish put anemone home before social group when bleaching strikes

Newcastle University

Marine heatwaves and anemone bleaching are altering clownfish behaviour, making clownfish more defensive of their host and more aggressive towards one another, new research reveals.

Led by Newcastle University and published in the journal Royal Society Open Science, the study explores how clownfish behaviour changed during the 4th Global Bleaching Event. During this event, the clownfish experienced a heatwave and their anemone partners bleached, meaning they lost their symbiotic algae, a stress response to elevated temperatures.

The results indicate that while elevated temperatures only had a small effect on clownfish behaviour, the bleaching response of the anemone altered how the animals spent their time. Bleaching led to more defensive behaviours, which could benefit the host anemone, and aggression between group members increased.

A group of Newcastle University students, led by PhD candidate Fletcher Noble, measured fish behaviour from video recordings made during a marine heatwave in Kimbe Bay, Papua New Guinea that lasted from March to July 2023. These were made during most extensive and intensive mass coral bleaching event in recorded history, spanning from 2023 to mid-2025 and known as the 4th Global Coral Bleaching Event.

The team analysed five behavioural categories: maintenance and defence, which help the anemone partner; and aggressive, neutral, and submissive behaviours, which maintain the fishes’ social group.

Their findings show that bleaching did not alter the large amount of maintenance behaviours towards the anemone that clownfish displayed, such as aeration and cleaning, while defence behaviours increased. This emphasises the crucial role of the mutualism between anemonefishes and anemones, where each partner depends on the other for defence against predators and nutrients. The aeration and defence done by clownfish during bleaching events may be important for anemones to recover from bleaching.

The potential trade-off, however, is that social cohesion may suffer in times of stress. Bleaching was linked to a 215% increase in aggressive behaviour between members of the clownfish social group.

Study lead author, Fletcher Noble, a PhD researcher at Newcastle University’s School of Natural and Environmental Sciences, said: “This research is one of the first to examine in detail how different types of clownfish behaviour change under bleaching conditions in the fish's natural environment. We revealed that clownfish are prioritising defending and maintaining their homes and securing their dominant position in the group during periods of environmental stress. In the future, we can examine these behaviours in even greater detail and explore how this may be helping the anemone recover from bleaching.”

Anemone bleaching and heat stress

Anemone bleaching occurs due to the loss of symbiotic algae and may turn the animal pale, white or translucent. It’s caused by increased stress, such as higher water temperatures and sun radiation.

In this study, while some of the hosting anemones bleached and lost symbiotic algae, others did not, allowing the researchers to estimate the effects of heat stress separate from the indirect effects through stressed mutualistic partners.

The study demonstrates that bleaching impacts behaviour more than thermal stress, with heat stress having no impact on the activity of clownfish, remaining stable as temperature dropped throughout the heatwave.

The research was featured in Blue Planet III, the highly anticipated return of BBC Studios Natural History Unit's landmark ocean series narrated by Sir David Attenborough.

Study senior author, Dr Theresa Rueger, Senior Lecturer in Tropical Marine Sciences, School of Natural and Environmental Sciences, Newcastle University, added: “As human activities continue to change ecosystems around the world, it is crucial to understand how species adapt their behaviour cope with environmental stress and habitat loss, since changing behaviours is animals’ first line of defence. The results show how important it is to consider interactions between different animal species and particularly mutualisms, where both species benefit, when researching the effects of environmental change.”

Reference

https://doi.org/10.1098/rsos.261623

--ends—

Images are available at: https://drive.google.com/drive/folders/1rw4lKmLHcnijdWm7NnR4J1M4eAso12jq Credit: Fletcher Noble