The study, published in the journal Discover Oceans, was led by Hai-Thanh Thi Nguyen of Nha Trang University together with Mackenzie Stoeltje and James Davis Reimer of the University of the Ryukyus, along with Viet Do Hung Dang of the Joint Vietnam-Russia Tropical Science and Technology Research Center. The team chose their study sites deliberately. Nha Trang Bay, once the center of coral reef research in Viet Nam, has suffered a catastrophic decline: between 2016 and 2018, most of its healthy coral communities were wiped out by outbreaks of crown-of-thorns starfish and Drupella snails, destructive fishing, sedimentation, and pollution from the rapidly growing city of Nha Trang. By 2019, coral abundance in the bay had fallen by more than 90 percent compared with earlier levels. Van Phong Bay, by contrast, is the largest bay in Khanh Hoa province, covering roughly 510 square kilometers, and is generally regarded as having good water exchange and environmental quality despite substantial aquaculture.

Using scuba-based roving diver surveys in September 2022, the researchers examined nine sites across the two bays at depths of one to twenty meters, spending a combined total of more than 950 minutes underwater. They measured every host anemone they encountered, recording its species, depth, and size, and documented every fish and invertebrate sheltering within reach of its tentacles. In total, they observed 94 host anemones belonging to seven species, including the bubble-tip anemone Entacmaea quadricolor, several Heteractis species, and three Stichodactyla species. They also counted 360 individual anemonefish representing four species: Amphiprion clarkii, A. sandaracinos, A. frenatus, and A. perideraion.

The differences between the two bays were striking. In Van Phong Bay, most anemones and anemonefish lived in water less than six meters deep, while in Nha Trang Bay the animals were concentrated between three and nine meters, and below twelve meters only one species, Heteractis crispa, was found. Perhaps most telling, the researchers found no anemones at all in the shallowest waters of Nha Trang Bay, even though historical records from 1996 show that host anemones there once ranged from the surface down to 27 meters. The anemone Cryptodendrum adhaesivum, once common in the shallow waters of Nha Trang Bay, has been encountered only once by the research team since 2015. The anemones that remained in Nha Trang Bay were also significantly smaller, averaging about 3,200 square centimeters, compared with more than 5,300 square centimeters in Van Phong Bay.

The authors suggest that the loss of shallow coral reefs in Nha Trang Bay is one plausible factor behind the disappearance of shallow-water anemones, although they caution that the relative roles of bleaching, poor water quality, predator outbreaks, and natural habitat differences remain unresolved. Environmental data collected from monitoring stations support the contrast between the bays: Nha Trang Bay showed significantly lower pH and higher total suspended solids, consistent with its documented sedimentation and pollution loads. Similar losses of shallow-water anemones and other reef anthozoans have been reported near urban centers elsewhere in the Indo-Pacific, including Singapore, Jakarta, and Okinawa, suggesting the Vietnamese pattern is part of a broader regional trend.

Beyond the famous clownfish, the study revealed a hidden cast of characters living among the anemone tentacles. The researchers recorded 325 individuals of other fish and invertebrate species associated with host anemones, including juvenile threespot dascyllus damselfish, cardinalfish, gobies, three species of cleaner shrimp, and the spotted anemone crab Neopetrolisthes maculatus. The sexy shrimp Thor amboinensis was the most common crustacean symbiont, recorded 33 times, followed by the red-banded coral shrimp Stenopus hispidus. Notably, no anemones were observed without anemonefish, meaning every host in both bays was occupied, and juvenile damselfish coexisted alongside the clownfish rather than taking over vacant hosts as has been seen in Okinawa.

The analysis also uncovered clear patterns of host specificity. Amphiprion sandaracinos was strongly associated with Stichodactyla mertensii, A. frenatus with Entacmaea quadricolor, and A. perideraion with Heteractis magnifica and H. crispa, echoing host preferences documented in previous studies. Two anemonefish species shared the same host in roughly one in five anemones, with A. clarkii and A. sandaracinos cohabiting most frequently. A multivariate analysis grouped the anemone-associated communities into clusters corresponding to anemone genera, with cleaner shrimp and crabs each showing preferences for particular host lineages. Correlation analysis revealed both positive associations, such as between cardinalfish and cleaner wrasses, and negative ones, including a moderate negative correlation between A. clarkii and A. frenatus that may reflect interspecific competition.

When the researchers applied diversity metrics, a nuanced picture emerged. Alpha and gamma diversity of anemones and anemonefish showed no significant differences between the bays, but beta diversity, the variation in community composition among sites, was higher in Nha Trang Bay and had a more nested structure, meaning species-poor sites contained subsets of the species found at richer sites. Crucially, when the two most degraded sites in Nha Trang Bay, located on the southwest of Hon Mun Island and affected by tourism, suspected illegal fishing, and storm damage, were excluded from the analysis, the differences in beta diversity between the bays largely disappeared. Permutational multivariate analysis of variance reinforced this interpretation: bay identity explained only about 2.3 percent of the variation in associated community composition, while site-level structure explained roughly 11 to 12 percent and was statistically significant across analyses.

This site-level signal carries an important management message. The authors argue that marine protected areas should not treat an entire bay as a homogeneous unit, but instead identify and prioritize unusual or vulnerable sites within each bay. The two most degraded sites in Nha Trang Bay contributed disproportionately to the nestedness component of beta diversity, a statistical fingerprint of disturbance. Tourism is a cornerstone of the Khanh Hoa economy, contributing an estimated 10 to 15 percent of provincial GDP, and much of that industry depends on the very reefs and reef creatures that draw visitors underwater. Diving has already been prohibited in the core zone of the Hon Mun Marine Protected Area since 2022, and the effectiveness of such measures will depend on enforcement and continued monitoring.

The study also documents what has already been lost. Nine species of host anemones were reported from Khanh Hoa two decades ago, but two of them, Cryptodendrum adhaesivum and Macrodactyla doreensis, were not found in the current surveys. Five anemonefish species are known from the province, including the saddleback clownfish A. polymnus, which depends on the anemone Stichodactyla haddoni, a species popular in local aquarium shops and now rare on the reefs. The authors are careful to acknowledge the limitations of their work: the sampling was unbalanced between bays, benthic habitat data were not collected, and environmental measurements came from stations several kilometers from the survey sites. Even so, the message is clear. Anemone communities are more than just clownfish and their hosts; they are hubs of reef biodiversity supporting damselfish, cardinalfish, cleaner shrimp, crabs, and the cleaning stations that keep reef fish healthy. Protecting them means protecting the water quality, coral habitat, and local conditions that allow these miniature cities of the reef to thrive, and the researchers hope future monitoring across Viet Nam and Southeast Asia will build on this first detailed look at an anemone-associated community under human pressure.

Subject of Research: Comparative ecology of sea anemone and anemonefish communities in reefs under different levels of human impact in Viet Nam

Article Title: Differences in communities of anemones, anemonefish, and other associated species between two bays under different levels of anthropogenic impacts in Viet Nam

Article References: Differences in communities of anemones, anemonefish, and other associated species between two bays under different levels of anthropogenic impacts in Viet Nam. (n.d.). https://doi.org/10.1007/s44289-026-00153-1

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00153-1

Keywords: anemonefish, sea anemones, coral reefs, Viet Nam, Nha Trang Bay, Van Phong Bay, symbiosis, beta diversity, anthropogenic impacts, cleaner shrimp, marine conservation, crown-of-thorns starfish

The study, published in the journal Ecology and Evolution, reports the results of a survey tracking coral feeding scars and surviving coral tissue after predation by individual crown-of-thorns starfish. The fieldwork was carried out at the University of Sydney’s One Tree Island Research Station on the southern Great Barrier Reef, in protected areas where healthy populations of fish and other predators keep the starfish at naturally low densities. In these balanced conditions, the researchers found something surprising: living coral tissue remained after almost 75 percent of the starfish feeding events they examined.

Dr Shawna Foo, a University of Sydney Horizon Fellow in the School of Life and Environmental Sciences who led the research, explained that the starfish at One Tree Reef behave very differently from the destructive swarms that have plagued other parts of the Great Barrier Reef. Rather than demolishing an entire coral colony in a single assault, starfish at low density appear to consume a relatively consistent amount of coral during each meal before moving on to another colony. This grazing pattern frequently leaves live coral tissue remnants behind, giving the corals a chance to recover.

That distinction matters enormously for how scientists and reef managers understand the species. Crown-of-thorns starfish are native to the Great Barrier Reef, where they have long been part of the ecological fabric. Since the 1960s, however, the reef has experienced four major outbreaks, erupting at intervals of approximately 15 years, each capable of causing mass coral destruction. The new findings do not diminish the significance of these devastating events, which coral populations struggle to recover from. Instead, they highlight an overlooked upside of low-density starfish populations functioning within a healthy marine ecosystem.

The mechanism behind the starfish’s constructive role lies in the competitive hierarchy of corals themselves. On many reefs, fast-growing species in the family Acroporidae, which includes the familiar branching and table corals of the genus Acropora, can rapidly colonize available space and shade out slower competitors. The study found that remnants of these fast-growing Acroporidae corals did not regenerate over the feeding scars left by starfish. Regeneration occurred mostly among much slower-growing Montipora and massive Porites corals, which gradually reclaimed the damaged areas. By preferentially trimming back the dominant, fast-growing species, low-density starfish populations open space for slower-growing corals to persist.

In effect, the starfish act as reluctant gardeners, pruning the most aggressive competitors and preventing any single coral species from monopolizing the reef. This increases the structural and taxonomic diversity of the coral community, a quality widely associated with healthier, more resilient reef ecosystems. Foo noted that by feeding on fast-growing corals such as Acropora, low-density populations create space for slower-growing species, helping to increase overall coral diversity across the reef.

The results align closely with a foundational concept in ecology known as the intermediate disturbance hypothesis. Professor Maria Byrne, a co-author of the study, said the findings are consistent with this important framework in ecology and conservation. The hypothesis proposes that occasional, moderate disturbance within an ecosystem can actually help maintain biodiversity, because it prevents dominant species from excluding others while stopping short of the catastrophic damage that eliminates species altogether. Crown-of-thorns starfish feeding at low densities appear to fit this pattern precisely, applying a measured pressure that keeps coral competition in balance without pushing the system toward collapse.

Understanding when starfish shift from ecological regulators to reef destroyers is a central question for conservation. The balance appears to hinge on predation. Diminishing populations of crown-of-thorns predators, including the giant triton snail and multiple species of coral reef fishes, heighten the vulnerability of the Great Barrier Reef and marine environments worldwide to outbreaks. Where those predators thrive, as in the protected zones surveyed at One Tree Reef, starfish numbers remain low and their feeding becomes a modest, even beneficial, component of reef dynamics. Where predator populations have collapsed, starfish can multiply into swarms that consume coral faster than it can regrow.

The research also carries practical implications for how managers respond to outbreaks. Current control efforts rely heavily on culling programs in which divers inject starfish to remove them from affected reefs. Foo emphasized that the new findings can help determine when and why culling should occur, and what the ecological endpoint of a cull should be. Once an outbreak has been suppressed, she argued, the goal should not necessarily be to eliminate crown-of-thorns starfish entirely. Instead, culling needs to be complemented by strong marine management that protects the starfish’s natural predators and keeps populations in check, allowing the species to resume its natural role rather than tipping back toward destructive abundance.

The study, an observational survey of coral feeding scars conducted on the Great Barrier Reef, reframes one of the ocean’s most feared invertebrates as a species whose impact depends entirely on context. In a functioning ecosystem with its predators intact, the crown-of-thorns starfish is a native coral predator performing a role that has shaped reef communities for millennia. Only when that balance is disrupted does it become the reef-wrecker of popular imagination. For a Great Barrier Reef facing warming waters, bleaching and repeated outbreaks, the message from One Tree Island is a nuanced one: the enemy of corals can, in the right numbers, be part of their salvation, and conservation strategies that restore ecological balance may prove more powerful than eradication alone.

Subject of Research: The ecological role of crown-of-thorns starfish predation in maintaining coral reef biodiversity

Article Title: Crown-of-thorns starfish can help reefs thrive

Article References: Crown-of-thorns starfish can help reefs thrive. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: crown-of-thorns starfish, coral reefs, Great Barrier Reef, biodiversity, intermediate disturbance hypothesis, marine ecology, coral predation, One Tree Island, reef management, culling, Acropora, University of Sydney

Directly addressing the challenge of controlling CoTS outbreaks, a groundbreaking multidisciplinary study has revealed the starfish’s ability to detect chemical peptides through their spiny appendages—a sensory modality never before fully understood in this species. This discovery was led by research groups from the Australian Institute of Marine Science (AIMS), the University of the Sunshine Coast, and the Okinawa Institute of Science and Technology (OIST). They identified that CoTS spines not only serve as defensive structures but are also specialized organs for both sensing and secreting a complex array of bioactive peptides, some of which act as chemical cues that influence conspecific behavior beyond reproductive contexts.

Building upon this insight, the researchers synthesized peptides that mimic these naturally occurring chemical signals—termed Acanthaster attractins—that are capable of enticing CoTS at minute concentrations without eliciting toxic effects. In meticulously designed experimental assays, including toxicity tests with Artemia salina larvae, the synthetic peptide mixtures showed negligible lethality, confirming their safety for broader ecological applications. Behavioral assays in controlled flume tanks further demonstrated that CoTS are strongly attracted to streams infused with these synthetic peptides, spending significantly more time and exhibiting enhanced searching behaviors within these chemical gradients.

The implications of these findings for marine conservation and pest management are substantial. Currently, attempts to control CoTS populations primarily involve labor-intensive manual culling, which has limited efficacy across the vast and often inaccessible reef structures. The potential to lure aggregations of starfish using synthetic attractins could revolutionize management strategies by enabling coordinated removal of large groups, thus amplifying the impact of control efforts while reducing required human labor and associated costs.

At the molecular level, the research team employed advanced genomic and proteomic analyses to elucidate the range of peptides expressed and secreted by CoTS spines. Surprisingly, these peptides extend far beyond previously characterized defensive toxins, suggesting a sophisticated chemosensory communication system akin to pheromonal signaling found in other invertebrate taxa. This communication likely underpins behaviors critical to survival and reproduction, including swarming and aggregation, which until now remained poorly understood.

Experimental data from swim-tank assays showed that when exposed to the synthetic peptide cues, CoTS not only altered spatial distribution but also demonstrated increased meandering—a foraging-related movement pattern facilitating source localization. This nuanced behavioral modulation underscores the potential utility of synthetic peptides as behavioral modifiers in ecological interventions. Furthermore, the biophysical properties of the flume tanks ensured minimal turbulence and diffusion, validating the specificity of the peptide’s chemotactic effect and reinforcing the findings’ ecological relevance.

The translational prospects of this research extend into the realm of ecological chemistry and marine biotechnology, as the development of non-toxic, peptide-based attractants could complement or even replace traditional chemical deterrents and manual removal methods. Importantly, these peptides’ specificity to CoTS reduces risks to non-target species, addressing a crucial conservation consideration.

Looking ahead, scalable synthesis and field trials of Acanthaster attractins will be pivotal to determine their efficacy across diverse reef environments and CoTS population dynamics. Such developments could align with integrated pest management frameworks, combining chemical ecology insights with ecological monitoring and localized intervention to restore coral reef balance more effectively.

Marine scientists have long grappled with controlling CoTS outbreaks due to the starfish’s complex life cycle, wide dispersal, and cryptic behavior. This seminal work offers a novel avenue by leveraging intraspecific chemical communication pathways, thereby expanding the toolkit available to reef managers. The ability to manipulate CoTS behavior through peptide signaling reflects an emerging trend in pest ecology: targeting communication systems to disrupt or redirect harmful species without ecological collateral damage.

Professor Noriyuki Satoh, leading the Marine Genomics Unit at OIST, emphasized the innovative nature of this research: “Our findings challenge the traditional view of CoTS spines as purely defensive structures. Instead, we reveal their dual role as both sensory and secretory organs mediating complex behavioral outcomes through peptide signaling. Such insights open transformative potentials for developing targeted, ecologically harmonious control measures.”

This research not only deepens fundamental understanding of starfish biology but also exemplifies how molecular and behavioral ecology can converge to address pressing conservation challenges. The synthesis of bioactive peptides based on naturally occurring chemical cues represents a promising frontier for managing marine pest outbreaks, with applications that may extend to other ecologically impactful invertebrate species.

In terms of practical application, deploying peptide attractants on reefs could facilitate coordinated removal efforts during early outbreak detection, potentially preventing the wide-scale destruction that has plagued Indo-Pacific coral ecosystems. By concentrating CoTS populations, these attractins could also enable more efficient monitoring and rapid response actions, minimizing the ecological and economic consequences of CoTS outbreaks.

In conclusion, this pioneering study heralds a new era of bio-inspired intervention strategies, transforming a nuanced understanding of crown-of-thorns starfish chemical ecology into tangible, sustainable solutions for reef conservation. As marine ecosystems face unprecedented threats, innovations such as synthetic peptide attractants offer hope for preserving the vibrant biodiversity and ecological functions of coral reefs worldwide.

Subject of Research: Animals

Article Title: A family of crown-of-thorns starfish spine-secreted proteins modify adult conspecific behavior

News Publication Date: 18-Apr-2025

Web References:
– https://www.sciencedirect.com/science/article/pii/S2589004225004225?via%3Dihub
– http://dx.doi.org/10.1016/j.isci.2025.112161

Image Credits: Harris et al., 2025

Keywords: Marine conservation, Coral reefs, Reef building corals, Pheromones, Conservation genetics, Peptide hormones, Synthetic peptides, Chemical signals, Pest control, Invertebrates