Marine Ecology Progress Series

Coral spawning has evolved to occur during relatively calm hydrodynamic conditions. However, moderate to high surface winds are often present on spawning nights in specific regions, with many unknown impacts to the early life-history stages of corals. Here, we mechanistically examine the sensitivity of fertilisation and larval development to increasing wind speeds for four common species of hermaphroditic corals on the Great Barrier Reef: Acropora kenti, A. millepora, A. spathulata, and Platygyra daedalea. Wind intensities relevant to coral spawning seasons were simulated by downscaling location-specific, historical wind speeds to laboratory flumes. Generally, fertilisation success declined as duration of exposure increased and was often lowest at the highest wind intensity equating to 15 knots in situ. Embryo damage, deformity, and fragmentation increased with exposure time, but varied across species. Four days following spawning, damaged and fragmented embryos had the highest mortality rates (76-82% and 70-73%) compared to intact embryos (26% and 52%) for A. kenti and A. spathulata, respectively. Experimental parameters were used to fit a 3D Fluid Dynamics model with outputs confirming that water surface elevations, velocity, and turbulence energy increased by up to 10%, 40%, and 50% respectively as winds intensified, likely explaining the physical drivers of the deleterious effects observed. Overall, results from this study indicate that suboptimal spawning conditions reduce propagule production, which may diminish recovery potential, thus require consideration when planning management strategies to safeguard coral reproduction.

Synchronous spawning is a specialised adaptation to maximise fertilisation success in free spawning sessile invertebrates. There are many factors that drive and limit reproduction in such benthic invertebrates including localised hydrodynamic forcing, adult density dependence, and fine-scale gamete interactions, all of which are difficult to measure in situ. Therefore, measures to manage or restore reproductive populations of sessile invertebrates rely in part on adequate modelling of spawning processes at localised scales. Fertilisation kinetics of spawning events has been modelled for many free spawning marine invertebrate taxa, yet little work has been done to parameterise such models for hermaphroditic corals. This study used experimentally derived coral-specific parameters and optimisation protocols to improve model predictions of fertilisation outcomes for Acropora kenti (formerly A. "Maggie" tenuis) and A. digitifera. Three fine scale parameters that are difficult to measure experimentally - fertilisation efficiency (Fe), egg concentration (E0), and polyspermy block strength (tb) - were estimated using optimisation, and medians and 95% confidence intervals were derived for each parameter and species. For A. kenti the median optimised Fe value was 0.0194 (0.0027-0.0776), and tb was 0.1000 (0.1000-0.1000). For A. digitifera, the median optimised Fe value was 0.0013 (0.0002-0.0030), and tb was 10.0000 (2.4703- 10.0000). Further, sensitivity analyses suggest that kinetics models are the most sensitive to changes in Fe parameter values, as well as species-specific metrics like sperm swimming speed and egg size. Results will inform biophysical coral fertilisation models to better predict reproductive outcomes and support management decisions that safeguard natural reef recovery.

Mutualistic associations between benthic marine invertebrates and reef taxa are common. Sponge-dwelling gobies benefit from protection within sponge tubes and greater food availability. Sponge-dwelling gobies are hypothesized to increase sponge pump rates by consuming polychaete parasites, but such increases have not yet been demonstrated. We investigated the association between sponge-dwelling gobies (Elacatinus horsti) and two species of tube sponge (Aplysina lacunosa and Aplysina archeri) in Bonaire, Caribbean Netherlands. We visually assessed goby presence in sponges and used in situ methods with fluorescein dye to estimate feeding rates via pump rates. Aplysina archeri were more likely to host a goby than A. lacunosa. For both sponge species, pump rates of tubes with gobies were higher on average than those of tubes without gobies. Our observations, therefore, suggest that E. horsti associations with Aplysina are likely mutualistic relationships in which sponges benefit from higher feeding rates when gobies are present.

Interspecific scraping behaviors among large marine vertebrates may serve as an important mechanism for ectoparasite removal. Here, we present the first documented observations of shark-manta scraping interactions, which occurred in the Revillagigedo Archipelago, a remote marine protected area in the eastern tropical Pacific. Opportunistic video footage was collected at two dive sites between December 2024 and February 2025, capturing three discrete events in which Galapagos sharks (Carcharhinus galapagensis) initiated contact with three different oceanic manta rays (Mobula birostris). Using a focal-animal sampling approach, we quantified the number and rate of scraping events and categorized responses. Sharks scraped against mainly the ventral surfaces of mantas using their heads, gill regions, and lateral areas associated with high ectoparasite loads. Manta responses ranged from passive tolerance to active evasion, with the strongest reactions observed in response to the adult Galapagos shark. Scraping rates varied by site and shark size. These interactions occurred at or near established cleaning stations, suggesting that sharks may opportunistically use mantas as alternative cleaning substrates. While this may indicate behavioral plasticity among sharks, it raises concern about potential costs to mantas, particularly if some ectoparasites or pathogens are transferred. Our findings highlight the complexity of shifting ecological interactions among marine megafauna and underscore the importance of understanding behavioral responses to cleaning disruption for endangered oceanic mantas.

Oyster reefs provide key ecosystem functions, including the provision of habitat for fish. While their importance in supporting fish assemblages is widely accepted, an assessment of intertidal oyster reefs at night remains a knowledge gap. Documenting habitat use at night could reveal new species reliant on these systems and help uncover diel fish movements among structured and unstructured habitats. We hypothesise that habitat use will interact with time and habitat, whereby differences in fish assemblages between oyster reef and unstructured habitats would be greater during the day. In this study, we used infrared-capable remote underwater video stations (RUVS) to sample paired intertidal oyster reefs and unstructured habitat during day and night. Assemblages using these habitats during the day do not match those at night, consistent with diel shifts observed in similar habitats. Consistent with our hypothesis, during the day oyster reefs had higher diversity and richness than unstructured habitat, whereas both habitats had low diversity and richness at night. The high relative abundance of piscivores in oyster reefs during the day suggests reefs create food webs that extend beyond benthic matter and sustain higher trophic levels. Nighttime abundances and diversity in oyster reefs dropped to levels similar to those of unstructured habitats during the day and night, likely a product of temporal niche partitioning and dynamic predation risks. Nighttime studies were important in documenting a wider suite of species and can thus provide a more complete understanding of fish-habitat interactions. Furthermore, this study used novel methods that enabled depth and size estimation from a single camera unit. While still in its infancy, this can serve as a force multiplier in monitoring intertidal habitats and lead towards a cost-effective method for standardising day/night abundance measurements and obtaining fish size estimates.

Connectivity among isolated habitat patches via planktonic larval dispersal is crucial for maintaining the regional diversity of hydrothermal vents. Despite, increasing sophistication of techniques for simulating dispersal, limited information on biological and behavioural traits of vent-associated species has unknown affects on the applicability of these methods for conservation. Here we focus on the role of periodic reproduction on dispersal among hydrothermal vents, as periodic spawning has increasingly been observed in a variety of taxa. For generalizeability, we simulate the dispersal of larvae under treatments of periodic and aperiodic release timing at various depths, with a consistant but variable planktonic larval duration. Our results show a highly variable effect of periodicity on the characteristics and distribution of dispersal, which are heavily modified by the dispersal depth and source location. The capacity for reproductive periodicity to impact the among-site dispersal warrents further investigation into its prevelance and timing among vent-associated fauna.

Climate change and anthropogenic pressures are reshaping marine food webs, altering prey availability and affecting top predators. The European Shag (Gulosus aristotelis), a coastal demersal seabird, provides a valuable model for examining environmentally mediated dietary variation, given its trophic plasticity and capacity to adjust prey use according to local availability, while also allowing assessment of potential demographic consequences. This study investigated spatial and temporal variation in diet at two Portuguese colonies (Berlengas and Arrabida) between 2016 and 2024 and assessed long-term reproductive productivity at Berlengas. A total of 468 regurgitated pellets were analysed, and diet composition was quantified using the Index of Relative Importance (IRI). Generalised additive models were applied to assess environmental, spatial, and period-specific effects on diet composition, while reproductive productivity was modelled in relation to prey biomass. Diet variation was primarily explained by environmental predictors, including sea surface temperature, chlorophyll-a concentration, and zooplankton, whereas year per se had no significant effect, indicating environmentally mediated bottom-up effects. Spatial differences between colonies reflected contrasting prey field structures, and period-specific patterns suggested increased specialisation during breeding. Higher biomass of sandeels (Ammodytidae) was positively associated with reproductive output, whereas shifts toward lower-energy prey were associated with reduced productivity. These findings demonstrate that environmentally driven dietary change has measurable demographic consequences, underscoring the importance of bottom-up processes in shaping seabird population dynamics and informing conservation strategies under ongoing climate change.

With the increased frequency of marine heatwaves and related coral mass mortality events, it is imperative that we improve our understanding of coral reef recovery processes including how benthic community compositions can change over time. Coral reef benthic communities are influenced by many abiotic factors, but on most reefs local anthropogenic disturbances overshadow these factors thus obscuring their influence. Here, we leverage a dataset from a coral reef with very minimal local anthropogenic disturbance - the uninhabited southern coast of the worlds largest atoll (Kiritimati) - to assess spatial variation in benthic community composition three years after the mass coral mortality event driven by the 2015-2016 El Nino. Across forereef sites ranging from 7 to 22 m, scleractinian coral cover remained very low (6.9 {+/-} 0.4 % SE) while soft coral cover was < 1%. Coral cover was highest at deep sites (18-22 m compared to sites at 7-10 m depth) and exposed locations, where stress-tolerant corals likely made up a larger proportion of the coral community before the mass mortality event. Higher cover of crustose coralline algae at shallow exposed sites, fleshy macroalgae at deep sites, and turf algae at exposed locations were consistent with taxa-specific preferences for light, wave action, and sedimentation. The abundances of the most common genera of juvenile coral (Acropora and Pocillopora) were still low (< 1 juvenile colony per genus per site) and varied only with depth. These findings demonstrate how variation in pre-mortality coral composition can lead to differences in post-mortality benthic communities on low disturbance coral reefs.

The change in state of Caribbean coral reefs over the last 40 years has been characterized by phase shifts from scleractinian coral cover to macroalgal cover, the loss of structural complexity and a decline in biodiversity. Not only do scientists want to understand these changes, but also predict the future of coral reefs and their capacity for resilience. In particular, the loss of herbivory, due to declines in parrotfish and the sea urchin Diadema antillarum, has been implicated in many studies as a proximate cause of the coral to macroalgal phase shift. However, reports of the particular role of these putative herbivores have varied, with some studies claiming a causal role for parrotfish, others for Diadema and still others suggesting no such relationships. Often these studies just examined one response measure of coral reef biodiversity. In this paper, I report the relationship between parrotfish and Diadema to many metrics of reef organization surveyed simultaneously in the same transects in reefs outside and within the Marine Protected Area (MPA) of Grand Cayman, an island that has been affected by increasing tourism over the last 30 years. The magnitudes of the various measures of reef diversity reported here are consistent with those reported elsewhere. The relationships among those measures are consistent with those reported in some prior studies and inconsistent with others, reflecting the variation in responses documented in prior studies. The presence of sea urchins was associated with survey sites having higher levels of coral cover, lower levels of macroalgae cover, and lower densities of parrotfish than survey sites without sea urchins. Moreover, parrotfish abundance was associated with a decrease in coral cover and little relationship to macroalgae cover. Neither coral cover nor macroalgae cover was different in sites within the MPA compared to sites outside the MPA. I argue that the combination of site-specific local stressors and their interaction with global stressors makes it unlikely that any one island or even regional reef system could serve as an exemplar for Caribbean-wide reef degradation. Moreover, it is difficult to assess the potential for reef resilience in the face of the ongoing assaults from increasing tourism pressures and global climate change.

Floating life (obligate neuston) is a core component of the ocean surface food web. However, only one region of high neustonic abundance is known so far, the Sargasso Sea in the Subtropical North Atlantic, where floating life provides critical habitat structure and ecosystem services. Here, we hypothesize that floating life is also concentrated in other gyres with converging surface currents. To test this hypothesis, we collected samples through the eastern North Pacific Subtropical Gyre in the area of the North Pacific "garbage patch" (NPGP) known to accumulate floating anthropogenic debris. We found that densities of floating life were significantly higher inside the central part of NPGP than on its periphery, and there was a significant positive relationship between neuston abundance and plastic abundance. This work has important implications for the ecology and human impact of subtropical oceanic gyre ecosystems.

Understanding how populations respond to variability in environmental conditions and interspecific interactions is one of the biggest challenges of population ecology, particularly in the context of global change. Although several studies have investigated population responses to climate change, very few have explicitly integrated interspecific relationships when studying these responses. Here, we aim to understand the combined effects of inter- and intraspecific interactions and environmental conditions on the demographic parameters of a prey-predator system of three sympatric seabird populations breeding in Antarctica: the south polar skua (Catharacta maccormicki), and its two main preys during the breeding season, the Adelie penguin (Pygoscelis adeliae) and the emperor penguin (Aptenodytes forsteri). We built a two-species integrated population model (IPM) with 31 years of capture-recapture and count data, and provided a framework that allows estimating demographic parameters and abundance of a predator-prey system in a context where capture-recapture data are not available for one species. Our results showed that predator-prey interactions and local environmental conditions affect differently south polar skuas depending on their breeding state of the previous year. Concerning prey-predator relationships, the number of Adelie penguin breeding pairs showed a positive effect on south polar skua survival and breeding probability, and the number of emperor penguin dead chicks showed a positive effect on the breeding success of south polar skuas. In contrast, there was no evidence for an effect of the number of south polar skuas on the demography of Adelie penguins. We also found an important impact of sea ice conditions on both the dynamics of south polar skuas and Adelie penguins. Our results suggest that this prey-predator system is mostly driven by bottom-up processes and local environmental conditions.

Herbivores play an integral part in maintaining the health of coral reefs by suppressing the growth of algae and accumulation of sediment and facilitating coral growth. However, in predator-depleted systems where densities of herbivores are unnaturally high, grazing can have detrimental effects on corals through excessive bioerosion. Yet, these benefits and costs are rarely investigated concurrently, especially in eutrophic systems where grazers may play a disproportionate role. We used a year-long exclusion experiment to elucidate the effect of natural densities of the dominant herbivore (the sea urchin Diadema setosum) on coral communities in a heavily fished and eutrophic system (Hong Kong, China). To assess benthic community response to grazing, we monitored the survival and growth of three locally abundant coral species (Pavona decussata, Platygyra carnosus and Porites sp.), algal and sediment accumulation, and bioerosion of coral skeletons across seasons. We found that urchins maintained our experimental coral assemblages, and when excluded, there was a 25 to 75-fold increase in algal-sediment matrix accumulation. Contrary to predictions, there was no general response of corals to urchin presence; Porites sp. survivorship increased while P. decussata was unaffected, and growth rates of both species was unchanged. Surprisingly, P. carnosus experienced higher mortality and bioerosion of up to 33% of their buoyant weight when urchins were present. Therefore, under natural densities, sea urchins clear substrate of algae and sediment, increase survival, maintain growth rates and health of coral assemblages, yet can accelerate the bioerosion of species with porous skeletons following mortality.

O_LIProtected areas are a widely adopted resource management strategy for mitigating the consequences of global change and preserve functioning ecosystems. Long-term species monitoring programmes, aided by bio-logging technology, provide insights into the extent and spatial variation of areas occupied by wild animals and inform conservation and management. High-resolution GPS-acceleration data offer a more accurate understanding of animal behavior and area use, compared to location-based inference, emphasizing the significance of specific sites amid long-term climate change. C_LIO_LIWe based our case-study on the largest colony of little penguins (Eudyptula minor) located at Phillip Island. Based on a ten-year bio-logging dataset (247 individual tracks), we combine high-resolution bio-logging data from GPS-accelerometer loggers with proxies for resource availability (e.g. Sea Surface Tenperature, thermocline, water turbidity). Using machine learning techniques and Generalized Additive Mixed Models, we quantify the environmental factors determining spatio-temporal variability in foraging effort (defined as hunting time) across different breeding seasons and stages. C_LIO_LILittle penguins increased their hunting time by reducing spatial displacement (shorter step length) and diving deeper, with a slower increase in hunting effort below 10 m depth. In relation to environmental conditions, penguins increased hunting effort in coastal areas with high turbid and productive waters and decreased effort with increasing Sea Surface Temperature. This gives insights into how these animals allocate effort differently according to shifting environmental conditions. C_LIO_LIOur analysis offers crucial long-term insights into little penguin area usage in the Bass Strait at sufficient spatial and temporal resolution for management and conservation planning. The Bass Strait is facing intense climatic and anthripogenic pressures, and the findings here on intensity of area usage and strategy shifting according to environmental conditions, are of great relevance for the marine spatial planning currently under development along the coast. C_LIO_LIPolicy implications: High-resolution behavioral information obtained from bio-logging data using GPS-accelerometer tags provides understanding of how species shift strategies in response to environmental variability. This is vital to implement climate-adaptive conservation and management strategies. Given the growing availability of long-term accelerometer datasets within the ecological community, we recommend integrating such high-resolution information into conservation programs. C_LI

Fledging is a critical period of a seabird life cycle. Using satellite telemetry, we compared movements and survival proxies (transmission duration) of chinstrap penguin fledglings tracked in 2017 (n=8) and 2025 (n=17) relative to krill fishing vessel activity. In 2017, fishing vessels operated intensively near colonies during summer, resulting in early, frequent encounters (median 1.3 days post-fledging) and short transmission durations (median 9.2 days). In 2025, reduced fishing delayed encounters (median 10.0 days) and tripled tracking duration (median 24.0 days). Hidden Markov Models revealed that vessel encounters reduced the probability of transitioning from foraging to transit behavior ({beta} = -0.76), an effect stronger than the productivity ({beta} = -0.11). While 87.5% of 2017 fledglings ceased transmission prematurely within weeks (half of those right after entering areas intensively used by fishing vessels), 65% of 2025 fledglings survived beyond March, with half of those five transmitting until May after dispersing eastward to the South Orkney Islands. These findings suggest that spatiotemporal overlap with krill fisheries during the critical post-fledging window affected foraging behavior and was associated with shorter transmission durations. Our results support further research of post-fledging penguin ecology to better understand the potential impact of fishery, and, following the precautionary principle, support fishing seasonal protection of important areas during critical periods of krill predators life cycle.

Many benthic marine invertebrates disperse by releasing microscopic larvae carried by ocean currents to new sites, where they must settle into appropriate habitats and metamorphose to recruit. Species whose larvae settle in response to water-borne chemical cues live in topographically complex habitats. To study whether sinking in response to dissolved cues affects retention of larvae within complex habitats exposed to ambient water flow moving faster than larvae sink, we used the reef-dwelling sea slug, Phestilla sibogae, whose competent larvae stop swimming and sink in response to dissolved cue from their prey coral, Porites compressa. We conducted field experiments where dye-labelled water, neutrally buoyant particles, and larval mimics (particles that sank at the velocity of larvae of P. sibogae) were released together upstream of reefs of branching corals to determine if larval sinking in water above and within a reef affects larval retention within the reef. Wave-driven water flow measured above a reef in the field had instantaneous velocities peaking at 0.3 m s-1, driving slow net advection of water shoreward at [~]0.02 m s-1. Much slower wave-driven flow moved through the interstices within the reef. In this field flow, sinking by larval mimics caused their retention within a reef after dye-labelled water and neutrally buoyant particles had left. Such retention of sinking larvae within topographically complex benthic communities enhances successful recruitment by exposing larvae to high concentrations of cue for long periods, allowing them time to sink to surfaces, adhere, and undergo metamorphosis.

Mass mortality of reef-building stony corals has driven widespread community shifts towards reefs dominated by soft corals and macroalgae. Although physical competition for space between these organisms plays an important role, non-contact water-mediated interactions have been proposed to modulate organismal performance and community functioning, yet their independent effects remain poorly resolved. Here, we experimentally tested the hypothesis that water-mediated interactions generate non-additive effects on community productivity, altering ecosystem functioning during phase shifts. Using two controlled incubation experiments with representative stony corals, soft corals, and macroalgae, we compared monoculture baseline productivity with mixed assemblages across a gradient of biomass ratios mimicking phase shift scenarios. We found that reductions in stony coral biomass led to community-level declines in photosynthesis and calcification that exceeded expectations based on monocultures, indicating emergent negative effects of community restructuring. However, these effects were strongly species-dependent, with some assemblages showing only minor deviations from expectations, whereas others exhibited pronounced productivity losses. At the species level, both stony corals reduced photosynthetic efficiency in mixed assemblages, while soft corals maintained efficiency across treatments. Macroalgal responses diverged, with one species exhibiting reduced and another increased photosynthetic efficiency in mixed communities. These species-specific physiological responses scaled up to explain community-level deviations from expected productivity, suggesting that gains in productivity by certain taxa can partially offset, but not fully compensate for, losses in coral-driven functions such as calcification. Together, our findings indicate that sublethal, water-mediated interactions can reorganize holobiont functioning and lead to changes in ecosystem productivity, independent of direct physical competition. By altering community-wide energy acquisition and carbonate production, such interactions may reinforce feedback loops that accelerate ecosystem phase shifts. We argue that incorporating water-mediated interaction effects into ecological theory and ecosystem models is essential for predicting the stability and recovery potential of coral reefs and other transitioning ecosystems under climate change.

Reproduction, embryological development, and settlement of corals are critical for survival of coral reefs through larval propagation. Yet, for many species of corals, a basic understanding of the early life-history stages is lacking. In this study, we report our observations for ex situ reproduction in the massive reef-building coral Porites lobata across two years. Spawning occurred in April and May, on the first day after the full moon with at least two hours of darkness between sunset and moonrise, on a rising tide. Only a small proportion of corals observed had mature gametes or spawned (17 - 35%). Eggs were 185 - 311 m in diameter, spherical, homogenous, and provisioned with 95 - 155 Symbiodiniaceae algae. Males spawned before females, and ex situ fertilization rates were high for the first 2 hours after egg release. P. lobata larvae were elliptical, approximately 300 m long, and symbiotic. Just two days after fertilization, many larvae swam near the bottom of culture dishes and were competent to settle. Settlers began calcification two days after metamorphosis, and tentacles were developed 10 days after attachment. Our observations contrast with previous studies by suggesting an abbreviated pelagic larval period in P. lobata, which could lead to the isolation of some populations. The high thermal tolerance and a broad geographic range of P. lobata suggest this species could locally adapt to a wide range of environmental conditions, especially if larvae are locally retained. The results of this study can inform future work on reproduction, larval biology, dispersal, and recruitment of P. lobata, which could have an ecological advantage over less resilient coral species under future climate change.

Understanding habitat association of animals and how they change through ontogeny is critical to predict the likely effects of habitat change on populations. We investigated how fine scale habitat associations of three common coral reef damselfish species changed among life-stages on reefs surrounding Lizard Island, northern Great Barrier Reef. All three species showed distinct habitat selection at settlement, however the degree to which these initial associations changed through ontogeny were species specific. Pomacentrus amboinensis associated with sandy areas throughout all life-stages; Pomacentrus chrysurus settled to areas with high cover of sand and rubble, but displayed no clear habitat preferences as juveniles or adults. Pomacentrus moluccensis settled to areas with high cover of fine branching corals before shifting to areas with relatively high cover of soft corals as adults. We also compared two different approaches to estimate habitat selection; one that quantified the benthic composition within the approximate home range of individuals versus a more widely used approach of recording a single point underneath the focal individual when they were first observed. Although results were broadly similar, the benthic composition approach revealed details that was overlooked using the single point method. Decreases in the availability of any of these preferred benthic habitats may adversely affect future populations, therefore understanding habitat associations and their transitions among life stages will be crucial in predicting future reef fish communities under ongoing coral loss and habitat change. This will require to systematically study a broader range of species, integrating relevant spatial and temporal scales.

Chorusing is widespread across the animal kingdom. Animal calling behavior is often driven by phenological and environmental factors such as seasonality, lunar period, and temperature. Now, in the Anthropocene, factors such as increased anthropogenic noise levels are also affecting calling behavior. Many fish call in choruses to attract mates, but the dynamics that drive fish calling behavior have rarely been studied in the field. We investigated how seasonality, lunar period, ambient noise, and temperature influenced the calling behavior of two species of toadfish, the plainfin midshipman (Porichthys notatus) and putatively, the Atlantic midshipman (Porichthys plectrodon). Acoustic recordings from a two-year period in twelve different locations, spanning two ocean basins showed that midshipman chorus presence was driven by seasonality and lunar period. Furthermore, chorus frequency increased with increasing temperature. Chorus levels were strongly influenced by seasonality and increased somewhat with increasing noise levels. Taken together, these results indicate that midshipman calling behavior was strongly influenced by interacting environmental conditions. Understanding the various impacts of each driver will facilitate predictions of changes in midshipman calling due to future changes in environmental conditions.

Around the Perhentian Islands, coral reefs have been undergoing degradation, as is reported by coral reef monitoring programmes. Current coral reef surveys around the Perhentian Islands do not specifically monitor hosting sea anemone populations, nor do they include investigation of how sea anemone abundance correlates to live coral cover on reef sites. As sea anemones can compete with corals for suitable substrate, nutrients, and light availability, the current study was designed to explore hosting sea anemone abundance and distribution patterns around the Perhentian Islands, as well as assess the presence of significant correlations between sea anemone abundance and live coral cover. Two sites with hosting sea anemone populations were assessed, and data was collected for sea anemone species, formation type, hosting status, and resident Amphiprion species. Additionally, live coral cover estimates were calculated and tested for associations between coral and sea anemone abundance. In total, 403 hosting sea anemone formations were analysed. Statistical analyses revealed that at the research site Village Reef, sea anemones that were actively hosting were larger, and more often encountered in clustered formations. In addition, sea anemone cover was significantly negatively correlated to live coral cover. At research site Teluk Keke, actively hosting sea anemones were also larger, but no other tests revealed significant results at this site. The current study offers a first population analysis of hosting sea anemone assemblages around the Perhentian Islands and provides a preliminary exploration of the associations between hosting sea anemone presence and live coral cover on these reefs.