The significance of the study lies in a distinction that is often overlooked in public discussions of coral bleaching. When a reef survives a heatwave, headlines tend to celebrate survival itself. But as lead author David Juszkiewicz, a PhD candidate in Curtin’s Coral Conservation and Research Group, explains, survival is only half the equation. A damaged reef does not recover merely because some of its corals remain alive; it recovers because those surviving colonies produce eggs and sperm, fertilize them, and release larvae that settle, grow, and gradually rebuild the three-dimensional structure that thousands of other species depend on. Without successful reproduction, even a reef full of living corals is, in demographic terms, a population with no future.

This is why knowing the reproductive calendar of reef-building corals matters so much. Coral spawning is a remarkably synchronized phenomenon: colonies of the same species release their gametes in coordinated bursts, often tied to lunar cycles, water temperature, and other environmental cues. If scientists do not know when a given species spawns, they cannot measure whether that species is reproducing successfully after a disturbance, cannot detect sublethal heat stress that suppresses fertility, and cannot plan restoration work that depends on collecting eggs and larvae at precisely the right moment. The Curtin team set out to close that knowledge gap for Ningaloo’s most important reef-builders.

The researchers examined 20 massive coral colonies drawn from across Ningaloo Reef, focusing on the genus Porites, a group of slow-growing, long-lived corals that create and maintain much of the structural habitat throughout the Indo-Pacific. These corals can form enormous boulder-like colonies that persist for centuries, making them both ecological cornerstones and valuable archives of environmental history. By sampling the reproductive tissues of these colonies, the team could determine whether individual corals were developing eggs and sperm and therefore preparing to spawn.

The results revealed a clear pattern for two of the three species studied. Porites lutea and Porites lobata, both major contributors to reef construction at Ningaloo, showed evidence that they were preparing to spawn during the reef’s annual early autumn mass spawning period. This finding establishes the first reproductive baseline for these species at the site, giving scientists and managers a reference point against which future reproductive activity can be measured. If marine heatwaves strike the region in coming years, researchers will be able to return to these corals and assess whether their reproductive output has declined, a far more sensitive indicator of long-term reef health than survival alone.

The third species told a different story. Porites australiensis showed no signs of reproduction during either of the team’s sampling periods, suggesting that it may spawn at a different time of year entirely. That possibility raises an important complication: some of Ningaloo’s major reef-building corals may not follow the reproductive schedules assumed from studies elsewhere. The implication is that year-round monitoring of reproductive activity will be needed to build a complete picture of how different species contribute to reef recovery and how they respond, individually, to thermal stress. A single annual spawning survey could easily miss the reproductive peak of a species that breeds outside the conventional window.

Perhaps the most striking finding concerns geography. Ningaloo’s Porites corals appear to reproduce in early autumn, whereas populations of the same species recorded further north, near Dampier on the Pilbara coast, have been observed spawning in late spring and early summer. That seasonal offset is more than a curiosity. As senior author Associate Professor Zoe Richards, leader of the Coral Conservation and Research Group in Curtin’s School of Molecular and Life Sciences, points out, if Ningaloo’s corals are reproductively isolated from reefs just 300 kilometres to the north, those northern populations may be unable to replenish Ningaloo if its corals are lost to heatwaves or cyclones. The two regions would effectively function as separate genetic stocks, despite their relative proximity, meaning that larval connectivity between them cannot be assumed when planning conservation at a regional scale.

The practical consequences for restoration programs are immediate. Many modern reef restoration efforts rely on capturing coral spawn during spawning events, rearing the larvae, and resettling them onto degraded reef areas. Timing is everything in this work. If scientists miss a spawning event, they may have to wait an entire year for the next opportunity to collect reproductive material. A reliable reproductive calendar for keystone species like Porites lutea and Porites lobata allows managers to plan collection expeditions, laboratory work, and outplanting schedules with confidence, rather than gambling on an uncertain window. The new baseline transforms what was previously guesswork into a scheduled, repeatable operation.

Independent experts have welcomed the benchmark. Dr Thomas Holmes, Program Manager for the WA Reef Regen Program at the Western Australian Marine Science Institution, who was not involved in the study, emphasized that heat stress does not simply determine whether corals live or die. It can also reduce reproduction, meaning corals may produce fewer eggs and sperm for years after a major bleaching event. That delayed fertility cost makes reproduction one of the most important indicators of a reef’s long-term health and resilience. With a baseline now established for some of Ningaloo’s most important reef-builders, any future heatwave impact on the region can be assessed against measurable reproductive data, informing coral regeneration activities with evidence rather than assumption.

The project was undertaken with funding from the Minderoo Exmouth Research Station and involved co-authors from the Curtin University Medical Research Institute, James Cook University and The University of Western Australia. As climate change continues to push ocean temperatures upward, the study underscores a broader lesson for reef science: recovery is a reproductive process, not just a survival outcome. Reefs cannot rebuild themselves unless their corals successfully produce the next generation, and protecting that capacity requires knowing exactly when, where, and how it happens. For Ningaloo, the clock has finally been read; for reefs elsewhere, the message is that similar baselines are urgently needed before the next marine heatwave arrives.

Subject of Research: Reproductive timing and spawning patterns of massive Porites corals at Ningaloo Reef, Western Australia

Article Title: New insights into coral reproductivity could help protect our reefs

Article References: New insights into coral reproductivity could help protect our reefs. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: coral reproduction, Ningaloo Reef, Porites, coral spawning, marine heatwaves, reef recovery, coral restoration, Curtin University, Marine Biology, reef resilience, Western Australia, larval connectivity

Corallivores, animals that eat live coral tissue, occupy an ambivalent position on reefs. At least 128 fish species from 11 families feed on coral polyps, mucus, and skeleton, forming an important pathway that channels the energy produced by the corals’ photosynthetic symbionts up the food web. Yet skeletal-feeding species such as pufferfish, parrotfish, and some triggerfish bite off chunks of skeleton along with the tissue, leaving lesions that cost corals energy to repair, potentially reducing growth and reproduction, and sometimes acting as vectors for coral disease. On healthy reefs, these effects are generally considered modest, because corals can defend themselves and regrow. After a disturbance, however, the equation changes: with fewer colonies remaining, the feeding pressure concentrated on each survivor can rise sharply, raising concerns that corallivores might slow reef recovery precisely when it matters most.

Pufferfish are particularly well equipped for this kind of predation. Their beak-like tooth plates, fused into four powerful cutting surfaces and driven by strong jaw muscles, allow them to shear through hard-bodied prey of nearly any kind. At least five Arothron species are known to eat corals. Despite this, most evidence for their diets has come from snapshot gut-content analyses of dead specimens, and detailed field observations have focused almost entirely on Arothron meleagris in the tropical eastern Pacific, where coral diversity is low. How Arothron pufferfishes behave on the species-rich reefs of the western Pacific, and how they respond to bleaching, remained largely unknown until now.

Mei Kubota, Hajime Sato, and Yoichi Sakai of Hiroshima University conducted their observations between 2023 and 2025 on a protected shallow reef in front of Sesoko Station, covering roughly 2.56 hectares at depths of one to five meters. Because A. nigropunctatus bears distinctive black spot patterns, the team could identify individuals photographically and track the same fish across years, a methodological advantage that allowed them to account for individual differences in feeding preferences. Snorkeling observers kept a distance of at least five meters and discarded the first minutes of each session to avoid disturbing the wary fish. Across 190 observation sessions totaling 6,064 minutes, they recorded bites on hard corals, the epilithic algal matrix, sponges, and sand-buried prey, along with movement patterns tracked by handheld GPS.

The baseline picture, gathered in 2023 when the reef was relatively healthy, showed a flexible omnivore rather than a coral specialist. The pufferfish fed mainly on Acropora and Porites corals but also bit the epilithic algal matrix, a complex of filamentous algae and cyanobacteria, dug sand-buried invertebrates by jetting water from their mouths, and occasionally took sponges. Activity was remarkably even across the day, with swimming occupying nearly 78 percent of observation time and no significant diel pattern in feeding. The fish showed no territoriality, moved hundreds of meters during half-hour watches, and never displayed aggression toward one another. Fecal analysis confirmed the observational data: Acropora dominated the diet by both weight and frequency of occurrence before bleaching.

Then came 2024. From July to September, seawater temperatures around Sesoko Island reached record highs, triggering a mass bleaching event. At a nearby reef, coral cover collapsed from 70 percent to under 5 percent within months, and at the study site nearly all Acropora colonies eventually died. The researchers had, by accident of timing, a natural experiment. Dividing their data into four phases, one year before bleaching, immediately before, during, and one year after, they fitted generalized linear mixed models to the bite counts, using observation time as an offset and individual identity as a random effect.

The results were striking. Bites on Acropora, which had averaged about 6.5 per 30 minutes in 2023, fell to nearly zero during bleaching and remained almost absent a year later, with the only two feeding events recorded in 2025 directed at small juvenile colonies sheltering under rocks. Notably, the pufferfish never bit bleached Acropora colonies at all. Feeding on Porites, a more bleaching-resistant genus, stayed stable throughout. Meanwhile, bites on other scleractinian corals such as Lobophyllia and Favites increased significantly, and feeding on the epilithic algal matrix surged to roughly seven times the pre-bleaching rate. Water-blowing on sandy patches, used to expose buried prey, declined to zero, suggesting that heat stress may have disturbed the sand-dwelling fauna as well. The pufferfish even began biting Chalinula nematifera, a sponge that can overgrow and kill corals, a predation event the authors believe has never been reported before.

Perhaps the most intriguing observation concerns how the pufferfish handle sediment-laden algal turfs. These mats, which accumulate heavy sediment loads after disturbances, are known to inhibit coral larval settlement and to suppress feeding by many herbivorous fishes, which tend to swallow calcium carbonate sediment along with the algae. The researchers watched A. nigropunctatus bite the algal matrix, hold it in its mouth, and expel the sediment, effectively separating food from grit. Because pufferfish lack the pharyngeal crushing apparatus of parrotfish and routinely ingest calcified prey, they may be unusually tolerant of sediment. The authors hypothesize that this could give the species a previously overlooked functional role: removing sediment-laden turf and creating gaps in the substrate that coral larvae could colonize, a service that typical herbivorous fishes may not readily replicate.

The study also quantifies how little coral these fish actually remove. Using the mean dry mass of fecal fragments and average bite rates, the team estimated that each pufferfish consumes about 7.9 grams of coral skeleton per day, or roughly 2.9 kilograms per year. At the observed density of 8.7 individuals per hectare, that amounts to about 25 kilograms of coral per hectare annually, equivalent to just 2.5 grams of calcium carbonate per square meter, far below rates reported for A. meleagris in the eastern Pacific and small relative to coral calcification rates in Okinawa. The authors caution that their estimates are minimums, since fragments may be abraded during digestion, and that coral skeletons can persist in the gut for weeks, which may explain why earlier gut-content studies overestimated the species’ dependence on coral.

Taken together, the findings recast the blackspotted pufferfish as a facultative corallivore whose flexible foraging may buffer it through disturbances rather than amplify them. Instead of concentrating on the few surviving colonies after bleaching, as feared, the fish shifted toward algae and other resources, and its total coral consumption appears too low to hinder reef recovery. Whether the dietary shift carries hidden costs, such as reduced growth or reproduction in the medium term, remains an open question, as does the precise mechanism behind the avoidance of bleached Acropora. But on a reef still reeling from record heat, the pufferfish’s plasticity offers a rare note of ecological nuance: a coral predator that, in the short term at least, appears to step aside, and may even lend a jaw, when the reef needs room to rebuild.

Subject of Research: Foraging behavior and dietary flexibility of the facultative corallivorous pufferfish Arothron nigropunctatus in response to mass coral bleaching on Okinawan reefs

Article Title: Foraging behavior and short-term response to mass coral bleaching by the facultative corallivorous pufferfish Arothron nigropunctatus in Okinawa, western Pacific

Article References: Kubota, M., Sato, H., & Sakai, Y. (2026). Foraging behavior and short-term response to mass coral bleaching by the facultative corallivorous pufferfish Arothron nigropunctatus in Okinawa, western Pacific. Coral Reefs. https://doi.org/10.1007/s00338-026-02961-5

Image Credits: AI Generated

DOI: 10.1007/s00338-026-02961-5

Keywords: coral bleaching, pufferfish, Arothron nigropunctatus, corallivory, Okinawa, epilithic algal matrix, dietary shift, reef recovery, behavioral ecology, Acropora, Porites, Tetraodontidae