Does habitat availability determine geographical-scale abundances of coral-dwelling fishes?

The role of local-scale processes in determining large-scale patterns of abundance is a key issue in ecology. To test whether habitat use determines local and large-scale patterns of abundance of obligate coral-dwelling fishes (genus Gobiodon), the author compared habitat availability with the abundance of four species, G. axillaris, G. brochus, G. histrio, and G. quinquestrigatus, among four locations, from the southern Great Barrier Reef to northern Papua New Guinea. Habitat availability, measured at tens of meters, explained 47-65% of the variation in abundance of these species among geographic locations spanning over 2,000 km. Therefore, local-scale patterns of habitat use appear to determine much larger-scale patterns of abundance in these habitat-specialist fish. The abundances of all species, except G. brochus, were also closely associated with particular exposure regimes, independently of the abundance of corals. Broad-scale habitat selection for reef types within locations can most easily explain this pattern. The abundances of all species, except G. brochus, also varied among geographic locations, independently of coral abundances. Therefore, the abundances of these species are influenced by either geographic variation in local-scale processes that was not measured, or additional processes acting at very large spatial scales.     

Microhabitat use and prey selection of the coral-feeding snail <Emphasis Type="Italic">Drupella cornus</Emphasis> in the northern Red Sea

Corallivorous gastropods of the genus Drupella are known for population outbreaks throughout the Indo-Pacific region. Despite their potential to destroy wide areas of coral reef, prey preferences have never been analyzed with respect to prey availability, and juvenile ecology and food selectivity remain largely unknown. Here, the influence of water depth, coral abundance, colony shape, prey species, and intraspecific attraction among snails on distribution patterns, prey selection, and microhabitat use of D. cornus was studied in the northern Red Sea. Special emphasis was put on ontogenetic differences. The snails were most abundant in the shallowest reef zone (1 m depth). Adults were associated with several substrates and coral growth forms, whereas juveniles were highly cryptic and restricted to live branching corals. The genus Acropora was significantly preferred over other acroporid and pocilloporid corals. As revealed by resource selection ratios, Acropora acuminata was preferred by juveniles, A. selago by adults. In aquarium experiments, intraspecific attraction was high among both life stages. Overall, significant differences in juvenile and adult microhabitat and prey use suggest that juveniles have more specific habitat requirements, and indicate ecological impacts on coral communities different from that of adults. Prey preferences seem to depend on both coral genus and colony shape. Acropora corals provide the best combination of food and shelter and therefore determine distribution patterns of D. cornus.     

Synergistic effects of habitat preference and gregarious behaviour on habitat use in coral reef cardinalfish

Spatial distributions of coral reef fish species are potentially determined by habitat preferences and behavioural interactions. However, the relative importance of these factors and whether or not behavioural interactions reinforce or disrupt habitat associations are poorly understood. This paper explores the degree to which habitat and social preferences explain the association that three common coral reef cardinalfish species (Zoramia leptacanthus, Archamia zosterophora and Cheilodipterus quinquelineatus; family Apogonidae) have with coral substrata at Lizard Island, Great Barrier Reef. At diurnal resting sites, species were strongly associated with branching corals, with 80–90% of each species inhabiting one branching coral species, Porites cylindrica. Species were also highly gregarious, forming large con-specific and hetero-specific aggregations in coral heads, potentially reinforcing habitat associations. Three-way choice experiments were conducted to test fishes habitat preferences for living coral over dead substrata, for particular coral species, and the influence of gregarious behaviour on these habitat choices. The strength of habitat preferences differed among species, with Z. leptacanthus preferring live coral and P. cylindrica, A. zosterophora preferring P. cylindrica, whether live or dead and C. quinquelineatus exhibiting no preferences. All species were attracted to conspecifics, and for C. quinquelineatus and A. zosterophora, conspecific attraction resulted in stronger preferences for live corals. Gregarious behaviour also increased C. quinquelineatus associations with P. cylindrica. The relative strength of social attraction versus habitat preferences was investigated by comparing fish habitat preferences in the presence and/or absence of conspecifics. The presence of conspecifics on non-preferred rubble habitat reduced each species association with live coral. This study’s results indicate that in the field, habitat preferences and conspecific attraction combine to reinforce the association between cardinalfishes and a narrow range of coral substrata.     

Interactions Between Habitat Use and Patterns of Abundance in Coral-dwelling Fishes of the Genus <Emphasis Type="Italic">Gobiodon</Emphasis>

Coral-dwelling fishes from the genus Gobiodon are some of the most habitat specialised fishes on coral reefs. Consequently, we might expect that their population dynamics will be closely associated with the abundance of host corals. I used a combination of log-linear modelling and resource selection ratios to examine patterns of habitat use among eight species of Gobiodon in Kimbe Bay, Papua New Guinea. I then used multiple regression analysis to investigate relationships between the abundance of each species of Gobiodon and the abundance of the corals they inhabited. Each species of Gobiodon used one or more species of coral more frequently than expected by chance. The pattern of habitat use exhibited by each species of Gobiodon did not vary among reef zones or among reefs with different exposures to prevailing winds, despite changes in the relative abundances of corals among reef zones. This consistency in habitat use might be expected if the coral species inhabited confer considerable fitness advantages and, therefore, are strongly preferred. For most species of Gobiodon, abundances among reef zones and exposure regimes were correlated with the abundance of the coral species usually inhabited. Therefore, it appears that habitat availability helps determine abundances of most species of Gobiodon in Kimbe Bay. In addition to correlations with habitat availability, the abundances of G. histrio, G. quinquestrigatus, G. rivulatus (dark form) and the group others were also associated with particular reef zones and exposure regimes. Therefore, in these species, reef type appears to influence patterns of abundance independently of coral availability. In contrast to other species of Gobiodon, the abundance of the most specialised species, Gobiodon sp.A, was not closely associated with the abundance of the only coral species it inhabited. This study demonstrates that even for habitat specialised species, the relationship between habitat availability and abundance varies widely and is multiscale.     

Habitat associations of juvenile fish at Ningaloo Reef, Western Australia: the importance of coral and algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority.     

Habitat selection, facilitation, and biotic settlement cues affect distribution and performance of coral recruits in French Polynesia

Habitat selection can determine the distribution and performance of individuals if the precision with which sites are chosen corresponds with exposure to risks or resources. Contrastingly, facilitation can allow persistence of individuals arriving by chance and potentially maladapted to local abiotic conditions. For marine organisms, selection of a permanent attachment site at the end of their larval stage or the presence of a facilitator can be a critical determinant of recruitment success. In coral reef ecosystems, it is well known that settling planula larvae of reef-building corals use coarse environmental cues (i.e., light) for habitat selection. Although laboratory studies suggest that larvae can also use precise biotic cues produced by crustose coralline algae (CCA) to select attachment sites, the ecological consequences of biotic cues for corals are poorly understood in situ. In a field experiment exploring the relative importance of biotic cues and variability in habitat quality to recruitment of hard corals, pocilloporid and acroporid corals recruited more frequently to one species of CCA, Titanoderma prototypum, and significantly less so to other species of CCA; these results are consistent with laboratory assays from other studies. The provision of the biotic cue accurately predicted coral recruitment rates across habitats of varying quality. At the scale of CCA, corals attached to the “preferred” CCA experienced increased survivorship while recruits attached elsewhere had lower colony growth and survivorship. For reef-building corals, the behavioral selection of habitat using chemical cues both reduces the risk of incidental mortality and indicates the presence of a facilitator.     

Live coral repels a common reef fish ectoparasite

Coral reefs are undergoing rapid changes as living corals give way to dead coral on which other benthic organisms grow. This decline in live coral could influence habitat availability for fish parasites with benthic life stages. Gnathiid isopod larvae live in the substratum and are common blood-feeding parasites of reef fishes. We examined substrate associations and preferences of a common Caribbean gnathiid, Gnathia marleyi. Emergence traps set over predominantly live coral substrata captured significantly fewer gnathiids than traps set over dead coral substrata. In laboratory experiments, gnathiids preferred dead coral and sponge and tended to avoid contact with live coral. When live gnathiids were added to containers with dead or live coral, significantly fewer were recovered from the latter after 24 h. Our data therefore suggest that live coral is not suitable microhabitat for parasitic gnathiid isopods and that a decrease in live coral cover increases available habitat for gnathiids.     

Variation in the structure of epifaunal invertebrate assemblages among coral hosts

The high biodiversity of coral reefs is attributable to the many invertebrate groups which live in symbiotic relationships with other reef organisms, particularly those which associate with the living coral habitat. However, few studies have examined the diversity and community structure of coral-dwelling invertebrates and how they vary among coral species. This study quantified the species richness and composition of animals associated with four common species of branching corals (Acropora nasuta, A. millepora, Pocillopora damicornis, and Seriatopora hystrix) at Lizard Island in the northern Great Barrier Reef. One hundred and seventy-eight nominal species from 12 different phyla were extracted across 50 replicate colonies of each coral host. A single coral colony, approximately 20 cm in diameter, harbored as many as 73 individuals and 24 species. There were substantial differences in invertebrate species composition among coral hosts of different families as well as genera. Twenty-seven species (15% of all taxa collected) were found on only one of the four different coral species, which may potentially indicate some level of specialization among coral hosts. The distinct assemblages on different coral species, and the presence of potential specialists, suggests invertebrate communities will be sensitive to the differential loss of branching coral species resulting from coral reef degradation.     

Reef‐coral refugia in a rapidly changing ocean

This study sought to identify climate‐change thermal‐stress refugia for reef corals in the Indian and Pacific Oceans. A species distribution modeling approach was used to identify refugia for 12 coral species that differed considerably in their local response to thermal stress. We hypothesized that the local response of coral species to thermal stress might be similarly reflected as a regional response to climate change. We assessed the contemporary geographic range of each species and determined their temperature and irradiance preferences using a k‐fold algorithm to randomly select training and evaluation sites. That information was applied to downscaled outputs of global climate models to predict where each species is likely to exist by the year 2100. Our model was run with and without a 1 °C capacity to adapt to the rising ocean temperature. The results show a positive exponential relationship between the current area of habitat that coral species occupy and the predicted area of habitat that they will occupy by 2100. There was considerable decoupling between scales of response, however, and with further ocean warming some ‘winners’ at local scales will likely become ‘losers’ at regional scales. We predicted that nine of the 12 species examined will lose 24–50% of their current habitat. Most reductions are predicted to occur between the latitudes 5–15°, in both hemispheres. Yet when we modeled a 1 °C capacity to adapt, two ubiquitous species, Acropora hyacinthus and Acropora digitifera, were predicted to retain much of their current habitat. By contrast, the thermally tolerant Porites lobata is expected to increase its current distribution by 14%, particularly southward along the east and west coasts of Australia. Five areas were identified as Indian Ocean refugia, and seven areas were identified as Pacific Ocean refugia for reef corals under climate change. All 12 of these reef‐coral refugia deserve high‐conservation status.     

Discordant coral–symbiont structuring: factors shaping geographical variation of Symbiodinium communities in a facultative zooxanthellate coral genus,Oculina

Understanding the factors that help shape the association between corals and their algal symbionts, zooxanthellae (Symbiodinium), is necessary to better understand the functional diversity and acclimatization potential of the coral host. However, most studies focus on tropical zooxanthellate corals and their obligate algal symbionts, thus limiting our full comprehension of coral–algal symbiont associations. Here, we examine algal associations in a facultative zooxanthellate coral. We survey the Symbiodinium communities associated with Oculina corals in the western North Atlantic and the Mediterranean using one clade-level marker (psbA coding region) and three fine-scale markers (cp23S–rDNA, b7sym15 flanking region, and b2sym17). We ask whether Oculina spp. harbor geographically different Symbiodinium communities across their geographic range and, if so, whether the host’s genetics or habitat differences are correlated with this geographical variation. We found that Oculina corals harbor different Symbiodinium communities across their geographical range. Of the habitat differences (including chlorophyll a concentration and depth), sea surface temperature is better correlated with this geographical variation than the host’s genetics, a pattern most evident in the Mediterranean. Our results suggest that although facultative zooxanthellate corals may be less dependent on their algal partners compared to obligate zooxanthellate corals, the Symbiodinium communities that they harbor may nevertheless reflect acclimatization to environmental variation among habitats.

     

Habitat Selectivity and Reliance on Live Corals for Indo-Pacific Hawkfishes (Family: Cirrhitidae)

Hawkfishes (family: Cirrhitidae) are small conspicuous reef predators that commonly perch on, or shelter within, the branches of coral colonies. This study examined habitat associations of hawkfishes, and explicitly tested whether hawkfishes associate with specific types of live coral. Live coral use and habitat selectivity of hawkfishes was explored at six locations from Chagos in the central Indian Ocean extending east to Fiji in the Pacific Ocean. A total of 529 hawkfishes from seven species were recorded across all locations with 63% of individuals observed perching on, or sheltering within, live coral colonies. Five species (all except Cirrhitus pinnulatus and Cirrhitichthys oxycephalus) associated with live coral habitats. Cirrhitichthys falco selected for species of Pocillopora while Paracirrhites arcatus and P. forsteri selected for both Pocillopora and Acropora, revealing that these habitats are used disproportionately more than expected based on the local cover of these coral genera. Habitat selection was consistent across geographic locations, and species of Pocillopora were the most frequently used and most consistently selected even though this coral genus never comprised more than 6% of the total coral cover at any of the locations. Across locations, Paracirrhites arcatus and P. forsteri were the most abundant species and variation in their abundance corresponded with local patterns of live coral cover and abundance of Pocilloporid corals, respectively. These findings demonstrate the link between small predatory fishes and live coral habitats adding to the growing body of literature highlighting that live corals (especially erect branching corals) are critically important for sustaining high abundance and diversity of fishes on coral reefs.     

Specialization in habitat use by coral reef damselfishes and their susceptibility to habitat loss

While it is generally assumed that specialist species are more vulnerable to disturbance compared with generalist counterparts, this has rarely been tested in coastal marine ecosystems, which are increasingly subject to a wide range of natural and anthropogenic disturbances. Habitat specialists are expected to be more vulnerable to habitat loss because habitat availability exerts a greater limitation on population size, but it is also possible that specialist species may escape effects of disturbance if they use habitats that are generally resilient to disturbance. This study quantified specificity in use of different coral species by six coral‐dwelling damselfishes (Chromis viridis, C. atripectoralis, Dascyllus aruanus, D. reticulatus, Pomacentrus moluccensis, and P. amboinensis) and related habitat specialization to proportional declines in their abundance following habitat degradation caused by outbreaks of the coral eating starfish, Acanthaster planci. The coral species preferred by most coral‐dwelling damselfishes (e.g., Pocillopora damicornis) were frequently consumed by coral eating crown‐of‐thorns starfish, such that highly specialized damselfishes were disproportionately affected by coral depletion, despite using a narrower range of different coral species. Vulnerability of damselfishes to this disturbance was strongly correlated with both their reliance on corals and their degree of habitat specialization. Ongoing disturbances to coral reef ecosystems are expected, therefore, to lead to fundamental shifts in the community structure of fish communities where generalists are favored over highly specialist species.     

Macroalgae reduces survival of nursery‐reared Acropora corals in the Florida reef tract

Recent declines in coral populations along the Florida reef tract have prompted the establishment of coral restoration programs which raise coral species, such as the threatened Acropora cervicornis, in nurseries ready for outplanting. Large numbers of nursery‐reared coral colonies have been outplanted along the Florida reef tract in recent years, yet few studies have characterized benthic habitats that are considered optimal for colony survival. In 2016, we surveyed 23 A. cervicornis restoration sites, located at six different reefs in the upper Florida Keys. We examined the condition of the outplanted corals and quantified the benthic assemblages adjacent to the outplanted coral colonies. We found that where A. cervicornis survived for more than 1 year, the substrate significantly supported less brown macroalgae of the genus Dictyota than at sites where A. cervicornis had died. Coral survival was highest at sites with less than 15% Dictyota cover. These results suggest that the habitat conditions that supported Dictyota spp. were not conducive to A. cervicornis growth and survival. Restoration practitioners should avoid attaching nursery‐raised corals to substrate with Dictyota spp. cover greater than 15%.     

Habitat degradation drives increased gnathiid isopod ectoparasite infection rate on juvenile but not adult fish

Widespread coral mortality is leading to coral reef degradation worldwide. Many juvenile reef fishes settle on live coral, and their predator-avoidance behaviour is disrupted in seawater exposed to dead corals, ultimately increasing predation risk. Gnathiid isopods are micropredatory fish ectoparasites that occur in higher abundances in dead coral. However, the effect of seawater associated with dead coral on the susceptibility of fish to micropredators has never been investigated. We tested whether the infection rate of cultured gnathiid ectoparasites on individual damselfish, Pomacentrus amboinensis Bleeker 1868, from two different ontogenetic stages (juveniles and adults) was influenced by seawater exposed to three different treatments: dead coral, live coral, or no coral. Seawater treatments were presumed to contain different chemical properties and are meant to represent environmental changes associated with habitat degradation on coral reefs. Gnathiid infection of juvenile fish in seawater exposed to dead coral was twice as high as that of fish in live coral or no coral. Infection rates did not significantly differ between live coral and no coral treatments. In contrast to juveniles, the susceptibility of adults to gnathiids was not affected by seawater treatment. During experiments, juvenile fish mortality was relatively low, but was higher for infected fish (9.7%), compared to fish held without exposure to gnathiids (1.7%). No mortality occurred in adult fish that became infected with gnathiids. Our results suggest that chemical cues released from dead corals and/or dead coral colonisers affect the ability of juvenile, but not adult fish to avoid parasite infection. Considering increased habitat degradation on coral reefs and that gnathiids are more abundant in dead coral substrate, it is possible that wild juvenile fish may experience increased susceptibility to parasitic infection and reduced survival rate. This highlights the importance of including parasitism in ecological studies of global environmental change.

     

Habitat selection of the long‐nosed bandicoot,Perameles nasuta (Mammalia,Peramelidae), in a patchy urban environment

Habitat selection in an omnivorous marsupial, the long‐nosed bandicoot, Perameles nasuta Geoffroy, was investigated in an urban environment with both natural and highly modified habitats at North Head, New South Wales, Australia. Habitat use at both macro‐ and microhabitat scales was determined using live‐trapping, and P. nasuta was shown to be a habitat specialist at this site. At night, animals used open grass macrohabitats disproportionately more for foraging than other macrohabitats. Trap‐revealed macrohabitat use was supported by radiotracking three males. Lack of understorey and absence of leaf litter were the major microhabitat features affecting habitat choice, although soil type probably also had some effect. Open areas may provide a more abundant and/or accessible food supply for P. nasuta, although better manoeuvrability or increased visibility to detect predators may also be important. Diurnal nest sites, located using radiotracking, were primarily in dense scrub vegetation, often comprising introduced species of plants. The dependence of P. nasuta on: (i) dense undergrowth for diurnal nesting and temporary nocturnal sheltering; and (ii) open areas for foraging indicates the importance of conserving a mosaic of open and dense vegetation to ensure the continued persistence of this endangered population at North Head.     

Bottlenecks to coral recovery in the Seychelles

Processes that affect recovery of coral assemblages require investigation because coral reefs are experiencing a diverse array of more frequent disturbances. Potential bottlenecks to coral recovery include limited larval supply, low rates of settlement, and high mortality of new recruits or juvenile corals. We investigated spatial variation in local abundance of scleractinian corals in the Seychelles at three distinct life history stages (recruits, juveniles, and adults) on reefs with differing benthic conditions. Following widespread coral loss due to the 1998 bleaching event, some reefs are recovering (i.e., relatively high scleractinian coral cover: ‘coral-dominated’), some reefs have low cover of living macrobenthos and unconsolidated rubble substrates (‘rubble-dominated’), and some reefs have high cover of macroalgae (‘macroalgal-dominated’). Rates of coral recruitment to artificial settlement tiles were similar across all reef conditions, suggesting that larval supply does not explain differential coral recovery across the three reef types. However, acroporid recruits were absent on macroalgal-dominated reefs (0.0 ± 0.0 recruits tile^?1) in comparison to coral-dominated reefs (5.2 ± 1.6 recruits tile^?1). Juvenile coral colony density was significantly lower on macroalgal-dominated reefs (2.4 ± 1.1 colonies m^?2), compared to coral-dominated reefs (16.8 ± 2.4 m^?2) and rubble-dominated reefs (33.1 ± 7.3 m^?2), suggesting that macroalgal-dominated reefs have either a bottleneck to successful settlement on the natural substrates or a high post-settlement mortality bottleneck. Rubble-dominated reefs had very low cover of adult corals (10.0 ± 1.7 %) compared to coral-dominated reefs (33.4 ± 3.6 %) despite no statistical difference in their juvenile coral densities. A bottleneck caused by low juvenile colony survivorship on unconsolidated rubble-dominated reefs is possible, or alternatively, recruitment to rubble-dominated reefs has only recently begun. This study identified bottlenecks to recovery of coral assemblages that varied depending on post-disturbance habitat condition.     

Postsettlement movement patterns and homing in a coral-associated fish

Coral-associated gobies are highly specialized reef fishes withhigh host-coral fidelity. Flexibility in habitat choice, however,is important to compensate for potential habitat alterationor loss, but detailed information about the postsettlement movementbehavior of such gobies is lacking. We examined movement patternsin Gobiodon histrio, both under natural conditions and duringsubsequent field experiments, involving breeding pair or partnerremoval from 3 of the 4 investigation plots. Additionally, weinvestigated homing behavior, and 2 aquaria experiments weredesigned to assess home coral and partner recognition of adultfish taken from breeding pairs. Under natural conditions, themovement rate was high for single adults, whereas breeding pairsshowed high home-coral fidelity. Manipulations revealed littlechange of natural patterns except in single adults, which slightlydecreased their movement rate in the breeding pair removal plot.In the homing experiment, 17% of tested fish returned to theirhome coral even after displacement of 4 m, and homing successwas much higher at shorter distances (100% at 0.5 m, 53% at2.25 m). In the aquarium, G. histrio exhibited higher recognitionof its home-coral colony (75%) than of its breeding pair partner(60%). Our study shows that G. histrio frequently moves betweencorals, although this depends on the social status (juvenile,single adult, breeding pair) of the individuals. The high proportionand movement rate of single adults indicate low sensitivityto habitat alteration but also limited high-quality habitatsin which breeding pairs could be established. Hence, vulnerabilityto habitat loss increases when individuals breed.     

Using Agent-Based Models to Aid Reef Restoration: Enhancing Coral Cover and Topographic Complexity through the Spatial Arrangement of Coral Transplants

High coral cover and topographic complexity are favorable qualities of a healthy coral reef. Because coral reef restoration is expensive and coral growth is naturally slow, there is a need to strategically arrange coral transplants to maximize coral cover and topographic complexity. Similarly, it is important to understand how differences in the life history characteristics of coral transplants can influence changes in the structural attributes of coral reefs. This study utilizes agent‐based computer modeling to explore the different spatial scenarios of coral transplantation using corals with contrasting r‐ and K‐selected life histories. Spatial indexes are used to compare coral cover and topographic complexity at incremental time scales, within which disturbance events are of minor importance in spatial structuring. The outcomes of the model suggest that even‐spaced grided transplanting arrangements provide the fastest increase in coral cover and three‐dimensional habitat space (topographic complexity) across large temporal scales (<30 years) for corals with r‐selected life history strategies.     

Suppressed recovery of functionally important branching Acropora drives coral community composition changes following mass bleaching in Indonesia

Mass coral bleaching events may have disproportionate effects on branching corals, leading to coral community restructuring, reduced biodiversity, and decreased structural complexity. This affects overall reef health and resilience. Functionally important, fast-growing branching Acropora corals were a historically dominant and vital component of Indonesian reefs throughout the twentieth century, yet the genus is also one of the most vulnerable to external stressors. This study used long-term annual reef monitoring data from Indonesia’s Wakatobi Marine National Park (WMNP) to investigate the effects of a mass bleaching event in 2010 on Acropora and other branching corals, evaluate their post-disturbance recovery trajectories, and analyse shifts in coral community composition. Post-bleaching scleractinian coral cover decreased across study sites, with losses in branching corals especially evident. Long-term branching Acropora cover decreased significantly and failed to demonstrate the significant post-disturbance recovery of other branching corals (especially Porites). In areas characterised by relatively high branching Acropora cover (> 15% mean cover) prior to bleaching, long-term coral community composition changes have trended predominately towards branching and massive Porites and branching Montipora. The novelty and key contribution of this study is that results suggest suppressed recovery of Acropora in the WMNP. Contributing factors may include the Allee effect (inhibition of reproduction at low population densities), other forms of inhibited larval recruitment, direct and indirect spatial competition, and changes in the physical reef habitat. These findings have critical implications for this functionally important taxon, future reef conservation efforts, and overall reef health and resilience in the park.