The study, led by Josie F. Chandler of James Cook University and colleagues, quantified daily feeding rates for 565 individual starfish across five regions of the central, northern and far northern Great Barrier Reef, from Townsville and Cairns to Lizard, Princess Charlotte Bay and Cape Grenville. Between March 2023 and March 2024, the team conducted 208 Scooter-Assisted Large Area Diver-based surveys, a novel method in which divers use underwater scooters to cover large reef areas efficiently. In total, more than 2,600 fresh feeding scars were measured, each attributed with confidence to a single starfish feeding in isolation.

The feeding mechanism of the crown-of-thorns starfish is central to understanding its destructive potential. Like other sea stars, it can evert its stomach through its mouth and spread it over the surface of a coral colony, digesting living tissue externally. When fully extended, the stomach covers a planar area roughly equivalent to the starfish’s oral disc, but it can drape over complex three-dimensional surfaces such as branching corals. This means the actual amount of tissue consumed increases with the structural complexity of the prey, which helps explain the starfish’s well-documented preference for tabular and corymbose Acropora corals, the very corals most vulnerable to bleaching and storm damage.

To translate simple field measurements into ecologically meaningful quantities, the researchers used genus-specific calibration curves developed for 15 distinct coral morphotaxa. Each fresh feeding scar, identifiable by sloughing tissue, mucous coverage or bare white skeleton not yet colonised by turf algae, was measured for maximum diameter with a flexible tape. These linear dimensions were converted into two-dimensional planar area and three-dimensional tissue surface area. The number of days over which scars were assumed to accumulate was standardised according to scar persistence: five days during summer surveys, when water temperatures ranged from 27 to 31 degrees Celsius, and seven days during winter surveys, when temperatures ranged from 24 to 26 degrees Celsius.

Analysing the data required a combination of machine learning and mixed-effects statistics. Boosted Regression Tree algorithms were first used to identify which of ten candidate predictors, including body size, population density, coral cover, Acropora cover, season, month, water temperature, latitude, region and reef, had the strongest influence on feeding rates. Generalized linear mixed effects models were then fitted for three separate metrics: the number of coral colonies consumed, the combined planar area of all feeding scars, and the total three-dimensional tissue surface area consumed. The final models included starfish body size category, total coral cover category and population density, with site as a random effect.

The results were unambiguous. Body size was the strongest and most consistent predictor of daily feeding across all three metrics, with rates increasing markedly from the smallest size class, up to 15 centimetres, to the largest, above 40 centimetres. The predicted daily planar area consumed across all starfish averaged 164.04 square centimetres, with individual values ranging from just 1.58 to a remarkable 2,135.29 square centimetres per day. When expressed as three-dimensional tissue surface area, the mean rose to 900.46 square centimetres per day, with extremes approaching 7,421 square centimetres. Perhaps most striking, the largest starfish at sites with more than 50 percent coral cover consumed an average of 221.99 square centimetres of planar coral area per day, more than ten times the 18.86 square centimetres consumed by smaller individuals at sites with less than 15 percent coral cover.

Just as revealing was what did not matter. Population density, season, water temperature and latitude showed no significant effect on daily feeding rates, challenging long-standing assumptions in outbreak models that treat every starfish as an equal unit of destruction. Seasonal variation in feeding has been proposed in earlier work, potentially driven by temperature-mediated metabolic demand or seasonal gametogenesis, but this study’s design, spanning eight degrees of latitude and allowing temperature effects to be examined in isolation from reproductive cycles, found no such link. The authors caution that the observed temperature range was relatively narrow at two to three degrees Celsius, and laboratory studies have shown starfish metabolism does rise with temperature, suggesting ocean warming could still increase feeding pressure under future climate scenarios.

The influence of coral cover operated in an unexpected way. While the area of coral consumed increased significantly at high-cover sites, the number of colonies preyed upon did not. This indicates that starfish on coral-rich reefs are not attacking more colonies, but rather consuming larger bites from bigger, structurally complex colonies. Because branching corals such as Acropora pack far more tissue surface area into a given footprint than massive corals do, high-cover reefs effectively supercharge individual feeding rates. In this study, 78 percent of the variation in total coral cover was explained by Acropora cover alone. The findings align with previous research showing that when Acropora abundance exceeds 30 percent, crown-of-thorns starfish exhibit strong site fidelity and homing behaviour, whereas on prey-poor reefs they roam widely in search of food.

The absence of a density effect is also scientifically significant. Density-dependent feeding is well documented in other echinoderms, particularly sea urchins, but the starfish densities observed here, ranging from 1.69 to 73.68 individuals per hectare, are moderate compared to catastrophic outbreaks exceeding 1,000 starfish per hectare recorded elsewhere. The authors suggest that behavioural shifts tied to crowding may only emerge at extreme densities, or that per-capita feeding may simply be insensitive to density and instead governed by prey availability. Measuring individual feeding rates also becomes inherently difficult at very high densities, when feeding scars cannot reliably be matched to specific individuals.

Beyond its ecological insights, the study delivers a practical tool for reef managers. Because the size categories used match those routinely recorded by Great Barrier Reef culling teams, and the coral cover categories align with protocols of the Great Barrier Reef Marine Park Authority and the Australian Institute of Marine Science Long-Term Monitoring Programme, the predicted feeding rates can be applied immediately to existing survey datasets. Managers can combine local population size-structure with coral cover data to estimate cumulative feeding pressure in real time, forecast coral loss as either benthic area or tissue surface area, and reassess intervention thresholds. This replaces the older, cruder approach of assuming uniform per-capita feeding, which the new data show can badly misestimate the true impact of an outbreak.

The findings also carry a deeper warning about the future of the reef. If Acropora-dominated environments are essential for sustaining high starfish densities and rapid individual feeding, widespread coral loss from bleaching could eventually impose natural constraints on outbreaks, as starving populations in prey-depleted environments may collapse. Conversely, any recovery of complex coral habitats could amplify the destructive capacity of starfish that remain. The study’s context-dependent, size-structured feeding estimates offer a substantially more accurate foundation for modelling coral mortality, prioritising culling effort and, ultimately, buying time for one of the world’s most iconic ecosystems as it faces the compounding pressures of predation and climate change.

Understanding the diet of juvenile crown-of-thorns sea stars has been a focal point for researchers due to the species’ potential to devastate coral populations. The researchers conducted a series of controlled experiments and field observations, revealing that the herbivorous diet of young sea stars plays an essential role in their overall development, shaping both their physical growth rates and survival metrics. Consequently, these findings indicate that the early dietary choices of juvenile sea stars not only affect their immediate health and vitality but could also have far-reaching consequences on coral reef dynamics.

The research team meticulously tracked the growth of juvenile sea stars from different dietary backgrounds. Those that consumed more diversified herbivorous diets exhibited significantly improved growth rates compared to their counterparts fed on monocultures. This observation lends weight to the hypothesis that nutritional variety may be pivotal in the early life stages of these sea stars. The implications of this are profound; if a juvenile sea star is not provided with a balanced diet, it could be stunted in growth, ultimately affecting its ability to transition to corallivory in adulthood which is a critical phase for their survival and impact on the ecosystem.

Moreover, the timing of the ontogenetic shift—the transition from an herbivorous to a corallivorous diet—was also found to be closely linked to the dietary conditions during juvenile stages. This is crucial, as earlier transitions can lead to increased predation on coral tissues, exacerbating the decline of coral reef health. The findings suggest that the nutritional phases in juvenile life are not merely phases of growth but are instrumental in dictating future feeding behaviors, survival tactics, and overall ecological roles of these pivotal marine stars.

Interestingly, the research highlighted that the environmental conditions in which juvenile sea stars thrive greatly influence their dietary preferences and growth trajectories. Factors such as water temperature, salinity, and the availability of food sources were shown to have significant impacts. Sea stars living in nutrient-rich environments exhibited enhanced growth compared to those in harsher conditions. This intricate relationship emphasizes the broader ecological implications of environmental degradation and its potential to alter species dietary patterns and survival strategies.

The methodological frameworks employed in this study were both rigorous and innovative. Researchers used a combination of lab experiments and in-field studies to gather comprehensive data, blending statistical analysis with ecological modeling to present a well-rounded understanding of juvenile sea stars’ growth dynamics. By integrating various data streams, they were able to establish correlations between diet, growth, and the timing of the shift to corallivory with unprecedented clarity.

As marine ecosystems continue to face the pressures of climate change and anthropogenic impacts, understanding the adaptive capacities of species like the crown-of-thorns sea star becomes ever more critical. The findings from this study are a clarion call for marine conservationists, urging a deeper investigation into the nutritional ecology of juvenile life stages among various marine species. Such insights could inform management practices aimed at bolstering coral reef resilience against invasive species like the crown-of-thorns sea star.

The implications extend towards understanding potential interventions that may help mitigate the harmful impacts of this species on coral reefs. If managers can enhance juvenile growth through habitat restoration efforts that provide better nutritional conditions, they could potentially influence the broader coral reef ecosystem’s health. For instance, promoting the growth of algae and other food sources could be a strategic approach to supporting healthy juvenile growth rates and delaying their shift to a coral-eating diet.

Furthermore, the findings also spark debate regarding the future of coral reefs under changing environmental conditions. With rising ocean temperatures and increasing pollution levels, understanding how these factors affect juvenile crown-of-thorns sea stars must be prioritized. Continuous monitoring and research are needed to ascertain the adaptive potential of this species and similar organisms facing the dual pressures of climate change and habitat destruction.

In conclusion, the research conducted by Llarena et al. offers significant insights into the intricate relationship between diet and the growth of juvenile crown-of-thorns sea stars. This study not only reaffirms the critical link between nutrition and survival in marine species but also calls attention to the urgent need for conservation efforts aimed at preserving coral reef ecosystems. By fostering more resilient juvenile populations through optimized dietary conditions, there may be a feasible pathway to reversing some of the ecological damage wrought by these voracious sea stars.

As marine biologists continue to disentangle the complexities of marine ecosystems, studies like these illuminate pathways forward in maintaining the delicate balance within coral reefs. As the fight against coral degradation intensifies, understanding the dietary preferences and growth patterns of these juvenile sea stars becomes a pivotal element in marine ecology and conservation strategies aimed at preserving our planet’s vital underwater landscapes.

Subject of Research: Dietary impact on growth and survival of juvenile crown-of-thorns sea stars

Article Title: Diet of herbivorous juveniles modulates growth, survival, and the timing of the ontogenetic diet shift to corallivory in crown-of-thorns sea stars

Article References:

Llarena, D., Cabrera, M.C.G., Doll, P.C. et al. Diet of herbivorous juveniles modulates growth, survival, and the timing of the ontogenetic diet shift to corallivory in crown-of-thorns sea stars. Coral Reefs (2025). https://doi.org/10.1007/s00338-025-02783-x

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s00338-025-02783-x

Keywords: crown-of-thorns sea stars, juvenile diet, coral reefs, growth, survival, corallivory, marine ecology, conservation strategies, environmental conditions, dietary impact, coral degradation, ecological dynamics.

Blackwater photography, which involves night-time dives into open water to illuminate the largely unseen microscopic and juvenile marine life, has revolutionized marine biology observations. This non-invasive method enables scientists to document elusive species interactions under natural conditions, often hidden during daylight hours. The lead author, Gabriel Afonso, a Ph.D. student at William & Mary’s Batten School of Coastal & Marine Sciences and the Virginia Institute of Marine Science (VIMS), attributes the success of this study to advances in low-light imaging technologies and the dedicated efforts of adept divers.

The investigation revealed that various species of juvenile fish, including carangidae (young jacks), filefish, driftfish, and pomfrets, have adopted a novel behavioral strategy: carrying live larval tube anemones or button polyps in their mouths. Such behavior appears to be a form of defensive mimicry or chemical deterrence, where by harboring these stinging invertebrates, the juvenile fish gain protection against predation. This interaction may qualify as a biological alliance wherein both parties derive benefits, a concept rarely documented between pelagic actinopterygians and benthic anthozoans.

Marine ecologist and blackwater photography contributor Rich Collins, affiliated with the Florida Museum of Natural History, notes that these sightings are consistent with other rare behaviors observed through this methodology. For example, filefish have been documented carrying venomous box jellyfish in their mouths without harm, suggesting an evolved resistance or tolerance to the stings. This indicates that juvenile fish may capitalize on the noxious properties of certain invertebrates, effectively wielding them as living weapons during their vulnerable early life stages.

The biological mechanisms enabling these juvenile fish to handle stinging anthozoans without injury remain an intriguing area for further study. It is hypothesized that they may possess chemical immunity or behavioral adaptations that mitigate the nematocysts’ effects. Moreover, the evolutionary advantages conferred by these associations likely enhance survival rates during critical dispersal phases, providing a selective impetus for the emergence of such interspecies behavioral adaptations.

From the anemones’ perspective, being transported by agile juvenile fish may facilitate dispersal to novel habitats, expanding their geographical range beyond the limitations imposed by their typically sedentary nature. This form of biological transport represents a significant departure from passive larval dispersal mechanisms conventionally attributed to sessile cnidarians. Consequently, the study proposes that this partnership could constitute a previously unrecognized mode of mutualistic symbiosis within pelagic ecological contexts.

While adult reef fish have long been documented utilizing coral structures for resting, shelter, or feeding purposes, this research pushes the envelope by highlighting how open-water juvenile fish actively engage with anthozoans beyond the benthic zone. This evolving understanding underscores the dynamic complexity of marine ecosystems and the necessity of advanced observation techniques to capture these transient yet ecologically significant interactions.

The study’s detailed photographic records exemplify the power of combining technological innovation with dedicated fieldwork. By illuminating these subtle behavioral nuances, blackwater photography is shedding new light on marine biodiversity and animal behavior, prompting a reevaluation of fish-anemone relationships and their ecological implications. These revelations invite a broader scientific discourse on the adaptive strategies of juvenile marine organisms within predator-prey frameworks.

Ecologists anticipate that these findings will stimulate further experimental and observational research aimed at delineating the physiological traits that allow juvenile fish to safely manipulate stinging anemones. Understanding these mechanisms could reveal insights into chemical ecology, sensory biology, and evolutionary pathways that have remained obscured until now. This knowledge holds potential applications for biomimicry, conservation efforts, and the management of marine ecosystems under environmental stressors.

The research also accentuates the importance of interdisciplinary collaboration, integrating marine biology, ethology, and photography expertise to unravel complex natural phenomena. As the marine science community embraces blackwater methodologies, the anticipation of discovering more such uncharted interactions grows. These advances contribute profoundly to our holistic comprehension of oceanic life and reinforce the necessity for continued technological investment in marine exploration.

Lastly, this article invites the public and scientific community alike to appreciate the hidden wonders of the ocean’s twilight zones. By revealing the delicate interdependencies between fish and anthozoans, the research triggers curiosity and respect for marine biodiversity. It urges conservation efforts targeting fragile early life stages of marine fauna and emphasizes the interconnectedness that sustains oceanic health and resilience in the face of escalating anthropogenic threats.

Subject of Research: Animals
Article Title: Associations between fishes (Actinopterygii: Teleostei) and anthozoans (Anthozoa: Hexacorallia) in epipelagic waters based on in situ records
News Publication Date: 5-Sep-2025
Web References: https://onlinelibrary.wiley.com/doi/10.1111/jfb.70214
References: DOI: 10.1111/jfb.70214
Image Credits: Linda Ianniello
Keywords: blackwater photography, juvenile fish, sea anemone, mutualism, pelagic ecosystems, fish-anemone interactions, larval anemone, chemical defense, biological dispersal, marine symbiosis, Actinopterygii, Hexacorallia

The research, conducted by a team comprising Gomez, Kimura, and Nakamura, meticulously documents the feeding behaviors of six species of obligate corallivores. These fishes, which depend exclusively on coral for food, offer critical insights into the dynamics of coral reef ecosystems, especially during periods of environmental stress. As coral reefs face increasing threats from climate change, including sea temperature rise and ocean acidification, understanding the adaptive responses of these fishes becomes paramount.

Initially, the study focused on the feeding preferences of these corallivore fishes before the bleaching event. The researchers employed an array of methodologies, including direct observation and dietary analysis, to establish baseline data. This foundational knowledge is crucial, as it allows for a comparison of feeding patterns post-bleaching, enabling scientists to detect shifts or changes in behavior that may signal broader ecological impacts.

As the mass bleaching event unfolded, leading to coral tissue loss and the expulsion of symbiotic algae, the scientists observed a marked alteration in the feeding behaviors of the studied fish species. The loss of their primary food source forced these obligate corallivores to display varying degrees of dietary flexibility, adapting their feeding strategies to target less preferred coral species. This adaptability highlights an inherent resilience but also raises concerns regarding the long-term viability of these species given the frequency and severity of future bleaching events.

The findings suggest that each of the six species exhibited distinct feeding preferences and responses, with some species demonstrating a greater capacity to shift their diet than others. This differentiation could have significant implications for the future of coral reef ecosystems. For instance, if certain species are better adapted to shifting food resources, they may thrive in changing environments, potentially leading to shifts in community structures that could further influence reef dynamics.

Moreover, the researchers highlighted that while some fish may initially adapt their feeding habits, the long-term consequences of sustained coral loss could lead to population declines. This is particularly alarming given that these obligate corallivores play essential roles in maintaining the health and biodiversity of coral reefs. Their feeding activities not only help to control coral growth but also facilitate nutrient cycling within these complex ecosystems.

As the study continues, scientists are calling for ongoing research to monitor the health of obligate corallivore populations as the reefs undergo transformation. The insights garnered from this research underscore the importance of preserving coral habitats and addressing the root causes of climate change. Conservation efforts must be informed by ecological studies such as this to develop effective strategies that safeguard both corals and the fish species dependent on them.

The implications of this research extend beyond the confines of academic inquiry. The fate of coral reefs affects millions of people globally, including communities relying on these ecosystems for livelihoods through fishing and tourism. As such, the findings serve as a clarion call to policymakers regarding the urgent need for action to mitigate climate change and preserve marine biodiversity. By adopting sustainable practices and reducing greenhouse gas emissions, we hold the key to a future where coral reefs can thrive, along with the myriad species that depend on them.

Furthermore, the understanding of obligate corallivore responses to environmental stressors opens avenues for more targeted conservation initiatives. For instance, creating marine protected areas that consider the resilience of various fish species to disturbances could enhance the adaptability of these fish populations. Such measures will be necessary as we grapple with more frequent and severe coral bleaching events exacerbated by global warming.

Ultimately, the study by Gomez, Kimura, and Nakamura not only enriches our understanding of fish ecology in relation to coral health but also reinforces the intricate balance within marine ecosystems. As we face an uncertain environmental future, it is vital that we amplify our research efforts and bolster our conservation strategies based on scientific evidence. The future of coral reefs, and indeed the oceans, hangs in the balance, reliant on a concerted global response rooted in sound science and dedicated stewardship.

In conclusion, the recent findings regarding the differential feeding preferences and population responses of obligate corallivore fishes during a mass coral bleaching event present both an alarming picture of ecological vulnerability and a testament to the adaptability of marine species. As researchers like Gomez, Kimura, and Nakamura peel back the layers of these complex interactions, it becomes increasingly clear that immediate and concerted action is essential if we are to protect these vital ecosystems from the irreversible consequences of climate change.

Subject of Research: Obligate corallivore fishes and their feeding preferences during coral bleaching events.

Article Title: Differential feeding preferences and population responses of six obligate corallivore fishes during a mass coral bleaching event.

Article References:

Gomez, R., Kimura, L.Y. & Nakamura, T. Differential feeding preferences and population responses of six obligate corallivore fishes during a mass coral bleaching event.
Coral Reefs (2025). https://doi.org/10.1007/s00338-025-02751-5

Image Credits: AI Generated

DOI: 10.1007/s00338-025-02751-5

Keywords: Coral reefs, obligate corallivores, feeding preferences, coral bleaching, marine ecology, climate change, conservation.