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1. Prehistoric archives reveal evidence of predator loss and prey release in Caribbean reef fish communities

   https://doi.org/10.1073/pnas.2503986122  

   O’Dea, Aaron; Dillon, Erin M; Brandl, Simon J; Cramer, Katie L; Cybulski, Jonathan D; de_Gracia, Brígida; García-Méndez, Kimberly; Griswold, Katherine; Lin, Chien-Hsiang; Leray, Matthieu; et al (July 2025, Proceedings of the National Academy of Sciences)

   Understanding how humans have altered coral reef food webs remains challenging due to the absence of prehistoric baselines. Here, we use fish remains preserved in fossil and archaeological deposits from Panamá and the Dominican Republic to explore how Caribbean reef fish mortality patterns have changed over millennia. By quantifying accumulation rates of shark dermal denticles (scales) and bony fish otoliths (ear stones) in reef sediments, we assess relative fish abundance, while otolith size serves as a proxy for body size at death. Comparisons of these death assemblages suggest a 75% decline in shark-derived material and a 22% reduction in the sizes of human-targeted fishes—consistent with historical exploitation. This evidence of decline in large-bodied, higher trophic level fish remains coincided with a doubling in prey fish otolith accumulation and a 17% increase in their reconstructed body sizes. These patterns in time-averaged death assemblages align with effects of release from predation, documenting an often assumed (but rarely shown) cascading effect. In contrast, otoliths of predator-sheltered cryptobenthic fishes showed no change in either accumulation or size, suggesting that ‘‘bottom–up”environmental factors were not responsible for the observed changes. Together, these data indicate that pre-exploitation predator communities strongly controlled exposed prey fishes, but this “top–down” effect diminishes rapidly toward the food chain base, especially in predator-resistant groups. Understanding trophic cascades on Caribbean reefs requires studying systems before predator depletion. 

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2. Vacuums of the sea: Ecological function of large coral reef benthic scavengers in suppressing crown-of-thorns starfish (COTS) outbreaks

   https://doi.org/10.24908/iee.2025.18.1.n  

   Kayal, Mohsen; Lenihan, Hunter (July 2025, Ideas in Ecology and Evolution)

   Despite their drastic impacts on coral reefs, outbreaks of the coral-feeding seastar crown-of-thorns starfish (COTS), Acanthaster, have remained a scientific enigma. Significant efforts in coral reef conservation science have been dedicated to identifying natural predators able to exert demographic control on COTS and prevent population outbreaks. These efforts are motivated by empirical evidence showing that reefs within marine protected areas are less prone to COTS outbreaks than reefs open to fishing where potential COTS predators have been reduced or removed functionally from food webs. Research findings point towards COTS’ early life-stages as a major demographic bottleneck for COTS populations, with various reef fish and benthic organisms identified as preying upon the seastar. Yet, no species or species groups have been clearly identified as exerting enough top-down control to influence COTS population increases or prevent outbreaks. We report the benthic scavenging behavior of eagle rays (family Myliobatidae), a large-bodied predator, feeding in coral rubble fields of Kanaky New Caledonia, critical habitats where juvenile COTS find refuge and food and accumulate to produce population outbreaks. We argue that with their effective substrate-sucking feeding behavior, similar to vacuums of the sea, eagle rays may be a hitherto unidentified predator able to exert significant control on COTS populations. Eagle rays and other large benthic scavengers were previously neglected in the search for major COTS predators. Relatively little existing data show that eagle ray populations in Kanaky New Caledonia’s lagoon are more abundant inside than outside marine protected areas, which concords with the hypothesis that they could be responsible for the mitigation of COTS outbreaks as reported within reserves. We advocate for further investigations on the role of eagle rays and other large benthic scavengers in controlling COTS outbreaks, and the importance of preserving the unique ecological function of sea vacuums for coral reef conservation. 

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3. A healthy but depleted herd: Predators decrease prey disease and density

   https://doi.org/10.1002/ecy.4063  

   Lopez, Laura K.; Cortez, Michael H.; DeBlieux, Turner S.; Menel, Ilona A.; O'Brien, Bruce; Cáceres, Carla E.; Hall, Spencer R.; Duffy, Meghan A. (July 2023, Ecology)

   Abstract The healthy herds hypothesis proposes that predators can reduce parasite prevalence and thereby increase the density of their prey. However, evidence for such predator‐driven reductions in the prevalence of prey remains mixed. Furthermore, even less evidence supports increases in prey density during epidemics. Here, we used a planktonic predator–prey–parasite system to experimentally test the healthy herds hypothesis. We manipulated density of a predator (the phantom midge, Chaoborus punctipennis ) and parasitism (the virulent fungus Metschnikowia bicuspidata ) in experimental assemblages. Because we know natural populations of the prey ( Daphnia dentifera ) vary in susceptibility to both predator and parasite, we stocked experimental populations with nine genotypes spanning a broad range of susceptibility to both enemies. Predation significantly reduced infection prevalence, eliminating infection at the highest predation level. However, lower parasitism did not increase densities of prey; instead, prey density decreased substantially at the highest predation levels (a major density cost of healthy herds predation). This density result was predicted by a model parameterized for this system. The model specifies three conditions for predation to increase prey density during epidemics: (i) predators selectively feed on infected prey, (ii) consumed infected prey release fewer infectious propagules than unconsumed prey, and (iii) sufficiently low infection prevalence. While the system satisfied the first two conditions, prevalence remained too high to see an increase in prey density with predation. Low prey densities caused by high predation drove increases in algal resources of the prey, fueling greater reproduction, indicating that consumer–resource interactions can complicate predator–prey–parasite dynamics. Overall, in our experiment, predation reduced the prevalence of a virulent parasite but, at the highest levels, also reduced prey density. Hence, while healthy herds predation is possible under some conditions, our empirical results make it clear that the manipulation of predators to reduce parasite prevalence may harm prey density. 

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4. Viral predation pressure on coral reefs

   https://doi.org/10.1186/s12915-023-01571-9  

   Silveira, Cynthia B.; Luque, Antoni; Haas, Andreas F.; Roach, Ty N.; George, Emma E.; Knowles, Ben; Little, Mark; Sullivan, Christopher J.; Varona, Natascha S.; Wegley Kelly, Linda; et al (December 2023, BMC Biology)

   Abstract Background Predation pressure and herbivory exert cascading effects on coral reef health and stability. However, the extent of these cascading effects can vary considerably across space and time. This variability is likely a result of the complex interactions between coral reefs’ biotic and abiotic dimensions. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health. Results Here, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m −2 ) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations. Conclusions The results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web. 

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5. Deciphering the footprints of predator–prey interactions on coral reefs: seasonal dynamics and environmental drivers of reef halos

   https://doi.org/10.1007/s00338-025-02701-1  

   Lester, Emily K; Cuttler, Michael VW; Langlois, Tim J; Madin, Elizabeth MP (October 2025, Coral Reefs)

   Abstract Landscape-scale footprints of behavioural interactions between predators and prey can offer a window into the ecological dynamics of entire ecosystems. In coral reefs, a promising example of this phenomenon includes reef halos, which are bare patches of sand surrounding patch reefs. Reef halos form where the presence of predators restricts herbivory and other foraging activities to close proximity of shelter. Additionally, reef halos persist from year-to-year, are more prevalent in reefs with ostensibly intact predator populations, and are easily measured using satellite imagery. However, the stability of reef halos over short-term (i.e. monthly) scales and how they respond to environmental factors, has yet to be rigorously explored in coral reefs. Here, we used a remote sensing approach to investigate the magnitude of reef halo size fluctuations over time in the Ningaloo Reef, Western Australia, relative to a suite of environmental factors. Although reef halos appear to be a permanent feature of the seascape, the size of individual reef halos fluctuated widely over monthly scales, declining as sea surface temperature and regional upwelling (a proxy for nutrient delivery) increased. We did not find a relationship between halo prevalence and management zone, fish biomass, or patch reef area, which is inconsistent with studies of reef halo formation in other locations. Unravelling this discrepancy with the broader literature will require an in situ experimental approach. Overall, our results demonstrate that single snapshots in time of reef halo size may not be sufficient to yield accurate signals regarding interactions between predators, herbivores, and vegetation. 

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