Coral Recruitment Research Articles

Coral recruitment: patterns and processes determining the dynamics of coral populations.

Coral recruitment describes the addition of new individuals to populations, and it is one of the most fundamental demographic processes contributing to population size. As many coral reefs around the world have experienced large declines in coral cover and abundance, there has been great interest in understanding the factors causing coral recruitment to vary and the conditions under which it can support community resilience. While progress in these areas is being facilitated by technological and scientific advances, one of the best tools to quantify recruitment remains the humble settlement tile, variants of which have been in use for over a century. Here I review the biology and ecology of coral recruits and the recruitment process, largely as resolved through the use of settlement tiles, by: (i) defining how the terms 'recruit' and 'recruitment' have been used, and explaining why loose terminology has impeded scientific advancement; (ii) describing how coral recruitment is measured and why settlement tiles have value for this purpose; (iii) summarizing previous efforts to review quantitative analyses of coral recruitment; (iv) describing advances from hypothesis-driven studies in determining how refuges, seawater flow, and grazers can modulate coral recruitment; (v) reviewing the biology of small corals (i.e. recruits) to understand better how they respond to environmental conditions; and (vi) updating a quantitative compilation of coral recruitment studies extending from 1974 to present, thus revealing long-term global declines in density of recruits, juxtaposed with apparent resilience to coral bleaching. Finally, I review future directions in the study of coral recruitment, and highlight the need to expand studies to deliver taxonomic resolution, and explain why time series of settlement tile deployments are likely to remain pivotal in quantifying coral recruitment.

Microbial community structure and settlement induction capacity of marine biofilms developed under varied reef conditions

Coral larval settlement relies on biogenic cues such as those elicited by microbial biofilm communities, a crucial element of coral recruitment. Eutrophication can modify these biofilm-associated communities, but studies on how this affects coral larval settlement are limited. In this study, we developed biofilm communities on glass slides at four sites with increasing distance from a mariculture zone. Biofilms farthest from the mariculture area were more effective at inducing the settlement of Acropora tenuis larvae. These biofilms were characterized by a greater proportion of crustose coralline algae (CCA) and gammaproteobacterial taxa compared to biofilms from sites closer to the mariculture zone, which had a greater proportion of cyanobacteria and no CCA. These findings suggest that nutrient enrichment due to mariculture activities alters the composition of biofilm-associated microbiome at nearby reef sites and indirectly causes poor coral larval settlement.

Variability in composition of parrotfish bite scars across space and over time on a central Pacific atoll

Parrotfishes are conspicuous herbivores, microvores, and detritivores in coral reef ecosystems, and the impacts of their feeding, particularly their capacity to expose reef carbonate, have received much attention. In many cases, parrotfish assemblages have been shown to control algal proliferation and promote the settlement of corals and crustose coralline algae (CCA). In extreme cases, high densities of parrotfishes may negatively affect net reef accretion through bioerosion and targeted coral predation. Most evidence describing the impacts of parrotfish foraging on benthic community structure is based upon correlations between benthic composition and parrotfish behavior or abundance, with much less known about process-based change of individual parrotfish bite scars through time. Here, we estimated parrotfish bite selectivity and determined the change in benthic composition within parrotfish bite scars relative to change in the overall reefscape using data collected over a 12-month duration from the fore reef habitat at Palmyra Atoll. We identified 2150 parrotfish bite scars which appeared most frequently on turf algae covered substrata but also on coral, CCA, and encrusting macroalgae. Of those bites taken on live coral, 96% of scars returned to live coral within 12 months. Notably, adult coral survivorship in bite scars was higher than at randomly sampled coral-covered locations not affected by parrotfish bites. The exposed substrate within bite scars was most commonly colonized by the dominant benthic functional group in the area immediately surrounding the scar. We found little evidence of coral recruitment to bite scars (1/2150); however, CCA growth on bites initially on turf algae increased from 18.4 to 32.9% across the two time intervals. Our results suggest that benthic areas affected by parrotfish bites were more likely to undergo a successional shift to a more calcified state relative to unaffected benthic areas, indicating that parrotfish grazing helps maintain highly calcified coral reef ecosystems.

Analisis Kesehatan Terumbu Karang Berdasarkan Kelimpahan Ikan Herbivora Di Perairan Labuan Bajo

Coral reef ecosystem is one of the ecosystems located in coastal areas which has a very important role for the community, both economically and ecologically. Rock or scleractinian corals are the main building blocks of coral reef ecosystems. The connectivity of coral reef ecosystems with other ecosystems has a very large influence on the life cycle of reef fish such as spawning, rearing, foraging, and sheltering places. Herbivorous fish are that eat turf algae or macroalgae that inhibit the recruitment of new corals. Labuan Bajo is one of the tourism destinations in Indonesia, especially marine tourism. Coral reefs in Labuan Bajo cover 10.8% of the total area of coral reefs in Indonesia located in Nusa Tenggara. The purpose of this study was to determine the health of coral reefs in the waters of Labuan Bajo. This research will be carried out from September to October 2021. The coral reef data collection method used is the Underwater Photo Transect (UPT), and for reef fish is using the Underwater Visual Census (UVC) method. Based on the research results, the percentage of hard coral is 20.16% of the total stations and rubble is 32.24%. The abundance of fish in Labuan Bajo waters ranges from 1608.89 - 4600.00 ind/ha, where the average abundance is 2919.78 ind/ha. All stations got a health index value of 3, this is indicated by the low coral cover, high coral resilience, and low herbivorous fish biomass obtained.

Ramicrusta invasive alga causes mortality in Caribbean coral larvae

The settlement of coral larvae is an important process which contributes to the success and longevity of coral reefs. Coral larvae often recruit to benthic structures covered with crustose coralline algae (CCA) which produce cues that promote settlement and metamorphosis. The Peysonneliaceae Ramicrusta spp. are red-brown encrusting alga that have recently become abundant on shallow Caribbean reefs, replacing CCA habitat, overgrowing corals and potentially threatening coral recruitment. In order to assess the threat of Ramicrusta to coral recruitment, we compared the survival and settlement of Porites astreoides and Favia fragum larvae to 0.5 – 2 mg ml-1 solutions of Ramicrusta sp. or CCA as well as sterile seawater (control). In all cases larval mortality was extremely high in the Ramicrusta treatments compared to the CCA and control treatments. We found 96% (± 8.9% standard deviation, SD) mortality of P. astreoides larvae when exposed to solutions of Ramicrusta and 0 - 4% (± 0 - 8.9% SD) mortality in the CCA treatments. We observed 100% F. fragum larval mortality when exposed to Ramicrusta and 5 – 10% (± 10 – 20% SD) mortality in the CCA treatments. Settlement or surface interaction of larvae in the CCA treatments was 40 - 68% (± 22 - 37% SD) for P. astreoides and 65 - 75% (± 10 - 19% SD) for F. fragum. Two P. astreoides larva that survived Ramicrusta exposure did settle/surface interact, suggesting that some larvae may be tolerant to Ramicrusta. These results suggest that Ramicrusta is a lethal threat to Caribbean coral recruitment.

How Do Underwater Cultural Heritage Sites Affect Coral Assemblages?

Underwater cultural heritage sites (UCH), such as shipwrecks and sunken aircrafts, can provide physical structures to support coral recruitment and habitats for marine organisms. Conversely, these archaeological artifacts can also be detrimental to live coral and release pollutants into the environment. The military history of Guam has resulted in a high abundance of UCH sites on shallow coral reef habitats, and little is known about how these artifacts may affect the ecology of these natural systems. In this study, we used photogrammetry techniques to survey coral assemblages on both natural and artificial reef substrata. We statistically examined patterns in coral cover, diversity, richness, and 3D habitat complexity. Our results found significant differences in live coral cover and assemblage structure between natural and artificial reef substrata. The results from univariate modeling and multivariate analyses indicate that coral assemblage structure plays an important role in supporting 3D habitat complexity, and the archaeological artifacts themselves can be a significant source of habitat structure. There is still a lack of clarity as to the overall implications of archaeological artifacts on underwater habitats, and the approach described here can be applied elsewhere to better understand the ecological impacts of UCH sites on coral reefs.

Community-managed coral reef restoration in southern Kenya initiates reef recovery using various artificial reef designs

Monitoring of reef restoration efforts and artificial reefs (ARs) has typically been limited to coral fragment survival, hampering evaluation of broader objectives such as ecosystem recovery. This study aimed to determine to what extent AR design influences the ecological recovery of restored reefs by monitoring outplanted coral fragments, benthic cover, coral recruitment and fish and invertebrate communities for two years. Four AR designs (16 m2), unrestored controls and natural reef patches as reference (n = 10) were established in Mkwiro, Kenya. ARs consisted either of concrete disks with bottles, layered concrete disks, metal cages or a combination thereof. A mixture of 18 branching coral species (mainly Acropora spp.) was outplanted on ARs at a density of 7 corals m-2. After two years, 60% of all outplanted fragments had survived, already resulting in coral cover on most ARs comparable (though Acropora-dominated) to reference patches. Coral survival differed between ARs, with highest survival on cages due to the absence of crown-of-thorns sea star predation on this design. In total, 32 coral genera recruited on ARs and recruit densities were highest on reference patches, moderate on concrete ARs and low on cages. ARs and reference patches featured nearly twice the fish species richness and around an order of magnitude higher fish abundance and biomass compared to control patches. Fish abundance and biomass strongly correlated with coral cover on ARs. AR, reference and control patches all had distinct fish species compositions, but AR and reference patches were similar in terms of trophic structure of their fish communities. Motile invertebrates including gastropods, sea urchins, sea cucumbers and sea stars were present at ARs, but generally more abundant and diverse at natural reference patches. Taken together, all studied ecological parameters progressed towards reef ecosystem recovery, with varying influences of AR design and material. We recommend a combination of metal cages and layered concrete ARs to promote high fragment survival as well as natural coral recruitment. Ultimately, a longer period of monitoring is needed to fully determine the effectiveness reef restoration as conservation tool to support coral reef ecosystem recovery.

Percentage of Hard Coral Cover and Coral Recruitment on in Bangsring Beach, Banyuwangi Regency

One of the tourist attractions at Bangsring Beach is the condition of the coral reef ecosystem and unique marine biota that tourists can enjoy by snorkeling and diving. Based on research (Ekawati et al., 2021) using remote sensing, the area of live coral reefs on Bangsring Beach is as follows; 2005; 3.38, 2008; 2.61, 2011; 3.7, 2017; 3.98, 2020; 6.1 Ha). It can be said that the area of coral reefs increases yearly, although, in 2008-2011, it decreased by 32%. The results of the economic valuation explain that the (Total Economic Value) of the coral reef ecosystem in Bangsring Beach is 38.2 billion Rupiah/year or 2.9 billion Rupiah hectares/year. The use-value that has the largest economic value comes from tourism utilization of 25 billion or 60% of the Total Economic Value. The coral community structure includes Coral Branching, Coral Encrusting, Coral Massive, Coral Submaasive, and Coral Mushroom. Mushroom Coral is found solitary and shaped like a mushroom. The research data shows the average value of Bangsring Fish House cover is 82.5%. Fish house cover here is seen and assessed based on the presence of hard corals, soft corals, and algae. The average percentage of hard corals growing at the Bangsring Fish House was 30%, soft corals 21.5%, and algae 17.5%. Found 21 types of coral such as; Acropora, Favia, Turbinaria, Symphyllia, Goniastrea.

Differential size frequency distribution of hard coral colonies across physical reef health gradients in Northeast Peninsula Malaysia

The size structure of a hard coral population reflects key demographic processes such as death, growth, and recruitment, and provides clues into recent ecological dynamics. Shrinking time intervals between mass disturbances (e.g., mass coral bleaching) result in demographic events that impact coral reef health and functionality. Analysis of size frequency distribution (SFD) of hard corals enables post hoc assessments of such demographic events and improves monitoring of coral reef health. Here, we present the first demographic study of Malaysian coral reefs and show the SFD of 36 morpho-taxa (n=4066 colonies), recorded along 27 × 10 m belt transects across three distinctive sites. We demonstrate a preponderance of small colonies (i.e., <20 cm, 84% of recorded colonies) and significant differences of taxon-specific SFD across physical reef health gradients (i.e., coral dominated to rubble dominated reefs). Physically degraded sites were significantly and consistently lower in coral recruitment, density, and diversity, while cover of coral rubble was higher. SFDs of abundant taxa were more negatively skewed (i.e., large colonies) and leptokurtic (i.e., peaky) at physically degraded sites. However, intra-taxonomic comparison revealed that absolute colony size was generally smaller at physically degraded sites, specifically for slow-growing massive colonies, but was larger for fast-growing Acropora and Fungia. Importantly, absolute colony size ranges were narrower at rubble dominated reefs and colony abundance declined across all size classes, resulting in the preponderance of medium-sized colonies in populations with more negatively skewed SFD. Therefore, our results support the notion that coral dominated reefs are assembled by predominantly smaller colonies. Conclusively, these results manifest that both the largest and the smallest individuals are eliminated at low cover reefs and community heterogeneity is impoverished. Ultimately, we highlight taxa with a balanced SFD (e.g., massive Dipsastraea, Porites spp. (rus), and massive Porites) despite the more frequent recurrence of mass disturbances.

Stories told by corals, algae, and sea-urchins in a Mesoamerican coral reef: degradation trumps succession.

Understanding the mechanisms that allow the permanence of coral reefs and the constancy of their characteristics is necessary to alleviate the effects of chronic environmental changes. After a disturbance, healthy coral reefs display trajectories that allow regaining coral cover and the establishment of framework building corals. Through a comparative approach, in a patch reef partially affected by a ship grounding, we analyzed the successional trajectories in affected and unaffected sectors. Fleshy algae (which do not promote the recruitment of corals) dominated the reef surface irrespective of the impact of the ship grounding incident. Acropora species had near-zero contributions to community structure, whereas non-framework building corals like Porites sp. had a slightly higher recruitment. Cover of coral and calcareous crustose algae decreased over time, and neither the latter nor adult coral colonies had any effect on the occurrence probabilities of small corals. Sea urchin (Diadema antillarum) densities were generally low, and thus unlikely to contribute to reverting algal dominance. The successional trajectories of the community in the impacted and non-impacted sectors of the coral patch reef agree with the inhibition successional model, leading to the development of a degraded state dominated by fleshy algae. It is probable that the stability and resilience of this degraded state are high due to the ability of fleshy algae to monopolize space, along with low coral recovery potential.

The effect of artificial reef design on the attraction of herbivorous fish and on coral recruitment, survival and growth

Fish assemblages of different types of artificial reefs can differ greatly in abundance, biomass and composition, with some reef types harboring over five times more herbivores than others. It is assumed that higher herbivorous fish abundance results in a higher grazing intensity, affecting the benthic community by means of enhanced coral recruitment, survival and growth. Territorial fish species might affect this process by chasing away other fish, especially herbivores. In this study we compared the fish assemblage, territorial behavior and grazing intensity by fish on two artificial reef types: reef balls and layered cakes, differing greatly in their fish assemblage during early colonization. In addition, the effect of artificial reef type on benthic development and coral recruitment, survival and growth, was investigated. Although layered cakes initially harbored higher herbivorous fish biomass, this effect was lost during consecutive monitoring events. This seems to be the result of the higher territorial fish abundance around the layered cakes where almost four times more chasing behavior was recorded compared to the reef balls. This resulted in a more than five times lower fish grazing intensity compared to the reef-ball plots. Although macroalgae were effectively controlled at both reefs, the grazing intensity did not differ enough to cause large enough structural changes in benthic cover for higher coral recruitment, survival or growth. The high turf algae cover, combined with increasing crustose coralline algae and sponge cover likely explained reduced coral development. We recommend further research on how to achieve higher grazing rates for improved coral development on artificial reefs, for example by facilitating invertebrate herbivores.

Characteristics of The Bleached Microbiome of The Generalist Coral Pocillopora damicornis from Two Distinct Reef Habitats.

Generalist coral species may play an important role in predicting, managing, and responding to the growing coral reef crisis as sea surface temperatures are rising and reef wide bleaching events are becoming more common. Pocilloporids are amongst the most widely distributed and studied of generalist corals, characterized by a broad geographic distribution, phenotypic plasticity, and tolerance of sub-optimal conditions for coral recruitment and survival. Emerging research indicates that microbial communities associated with Pocilloporid corals may be contributing to their persistence on coral reefs impacted by thermal stress; however, we lack detailed information on shifts in the coral-bacterial symbiosis during bleaching events across many of the reef habitats these corals are found. Here, we characterized the bacterial communities of healthy and bleached Pocillopora damicornis corals during the bleaching events that occurred during the austral summer of 2020 on Heron Island, on the southern Great Barrier Reef, and the austral summer of 2019 on Lord Howe Island, the most southerly coral reef in Australia. Regardless of reef location, significant differences in α and β diversities, core bacterial community, and inferred functional profile of the bleached microbiome of P.damicornis were not detected. Consistent with previous reports, patterns in the Pocilloporid coral microbiome, including no increase in pathogenic taxa or evidence of dysbiosis, are conserved during bleaching responses. We hypothesize that the resilience of holobiont interactions may aid the Pocilloporids to survive Symbiodiniaceae loss and contribute to the success of Pocilloporids.

The 2022 Diadema antillarum die-off event: Comparisons with the 1983-1984 mass mortality

The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effects on Caribbean coral reefs. Without the grazing activities of this key herbivore, turf and macroalgae became the dominant benthic group, inhibiting coral recruitment and compromising coral reef recovery from other disturbances. In the decades that followed, recovery of D. antillarum populations was slow to non-existent. In late January 2022, a new mass mortality of D. antillarum was first observed in the U.S. Virgin Islands. We documented the spread and extent of this new die-off using an online survey. Infected individuals were closely monitored in the lab to record signs of illness, while a large population on Saba, Dutch Caribbean, was surveyed weekly before and during mortality to determine the lethality of this event. Within four months the die-off was distributed over 1,300 km from north to south and 2,500 km east to west. Whereas the 1983-1984 die-off advanced mostly with the currents, the 2022 event has appeared far more quickly in geographically distant areas. First die-off observations in each jurisdiction were often close to harbor areas, which, together with their rapid appearance, suggests that anthropogenic factors may have contributed to the spread of the causative agent. The signs of illness in sick D. antillarum were very similar to those recorded during the 1983-1984 die-off: lack of tube feet control, slow spine reaction followed by their loss, and necrosis of the epidermis were observed in both lab and wild urchins. Affected populations succumbed fast; within a month of the first signs of illness, a closely monitored population at Saba, Dutch Caribbean, had decreased from 4.05 individuals per m2 to 0.05 individuals per m2. Lethality can therefore be as high as 99%. The full extent of the 2022 D. antillarum die-off event is not currently known. The slower spread in the summer of 2022 might indicate that the die-off is coming to a (temporary) standstill. If this is the case, some populations will remain unaffected and potentially supply larvae to downstream areas and augment natural recovery processes. In addition, several D. antillarum rehabilitation approaches have been developed in the past decade and some are ready for large scale implementation. However, active conservation and restoration should not distract from the primary goal of identifying a cause and, if possible, implementing actions to decrease the likelihood of future D. antillarum die-off events.

Coral recruitment and its relationship to hard coral cover in the Derawan Islands, East Kalimantan

Coral recruitment is the process when coral larvae settle to the substrate and establish themselves as a reef community. The success of coral recruitment is very important for the sustainability of coral reefs in an area, including the Derawan Islands which develop underwater tourism. Observations on coral reef recruitment were carried out in the Derawan Islands. This study aimed to determine the density of coral recruitment, hard coral cover, and the relationship between coral recruitment and hard coral cover. Data were collected using the Underwater Photo Transect method at 11 stations in the Derawan Islands. The results showed that coral recruitment in the Derawan Islands was low, ranging from 1.41 to 3.13 colonies.m−2. Hard coral cover was categorized as “moderate” with an average of 28.04% (+SE=3.63%). The relationship between coral recruitment and hard coral cover occurred for medium-sized juvenile corals (3-6 cm). Their negative relationship was shown by the presence of more medium-sized juvenile corals in areas with lower hard coral cover. The large availability of stable substrates such as DCA in areas with low hard coral cover can increase the potential for coral reef ecosystems to recover naturally.

Multi-year coral recruitment study across the Florida Reef Tract reveals boom-or-bust pattern among broadcast spawners and consistency among brooders

Scleractinian coral populations are in global decline, and successful recruitment is fundamental to community persistence and recovery, but recruitment may vary by coral reproductive mode. Using settlement tiles, we assessed coral recruitment over 3 consecutive years across 4 regions (~300 km) of the Florida Reef Tract (FRT) to determine whether spatio-temporal variation differs between brooding and broadcast spawning corals and whether coral recruit distributions correlate with adult coral live tissue area, site temperature, or depth. We deployed 32 tiles to each of 30 sites with depths ranging from 2 to 18 m; tiles were retrieved and replaced annually. From 2016-2018, we counted 11633 scleractinian coral recruits, most of which belonged to the Siderastreidae, Agariciidae, Poritidae, and Faviidae families. Faviid recruits were rare (&lt;1%). While recruitment of brooding agariciids and poritids was relatively stable across the 3 yr, recruitment of broadcast spawning siderastreids increased an unprecedented 70.7-fold from 2017 to 2018, in a boom that spanned 19 sites across the FRT. Elevated temperature during the preceding reproductive season was a significant predictor of low recruitment for all groups except siderastreids and faviids, and recruitment of brooding taxa was positively linked to adult confamilial live tissue area. For siderastreids, adult live tissue area was also related to recruitment, but the direction of the relationship differed by year and region. The unprecedented high recruitment of siderastreids in Florida, preceded by 2 yr of comparatively low recruitment, demonstrates that broadcast-spawning scleractinians are among the marine taxa capable of employing boom-and-bust recruitment cycles over geographically widespread areas.

Recruitment of hard coral communities on giant clam shells (Cardiidae: Tridacna) differ from surrounding reef habitats at a tourist destination in the Gulf of Thailand

ABSTRACT Giant clams are organisms of significant ecological importance on coral reefs. They are known to help maintain oligotrophic conditions on reefs, to act as potential reservoirs of symbiotic dinoflagellates and as a consequence of their large, dense shells, to contribute to reef structural complexity. Despite this, little work has been done to investigate the utility of giant clam shells for coral recruitment. Here, we quantify scleractinian coral growth on living and dead giant clams around the Thai island of Koh Tao, a site with a history of environmental and anthropogenic pressure related to tourism. Transect surveys at 15 reefs around the island yielded 739 clams, of which 120 were found to support coral recruits. A total of 270 distinct corals were recorded between depths of 2.1 and 8 m (none were found at depths shallower than 2 m), with 29% found on dead shells and 71% on living clams. Differences were found in the community structure of hard corals found on clam shells vs those found in surrounding reef environments, with mushroom corals (Fungiidae) and Stylocoeniella being significantly more abundant on clam shells than on the natural reef. In contrast, corals abundant on surrounding reefs (e.g. Acropora and Porites) were disproportionately better represented on the reef than on clam shells. This suggests that giant clam shells may play a significant role in the succession of coral reefs with certain corals being preferentially supported over others.

Coral rubble dynamics in the Anthropocene and implications for reef recovery

AbstractWith rubble predicted to increase on coral reefs worldwide, we review the physical, biological, and ecological dynamics of rubble beds, with a focus on how rubble generation, mobilization, binding, and coral recruitment is expected to change on future reefs. Major disturbances, including storms and coral bleaching, are predicted to increase in intensity and frequency, and—like localized impacts including blast fishing and ship groundings—generate large quantities of coral rubble. Reefs will have increasingly smaller recovery windows between successive disturbances, leading to persistence of unstable rubble beds on reefs. With more severe storms and increased bioerosion on future reefs, rubble mobilization thresholds will be met more often as smaller, less complex rubble pieces are generated. If rubble remains stable for adequate time, it can be bound by organisms including sponges and coralline algae, and eventually be cemented. However, increasing rubble mobilization frequencies will reduce the time available for binding, while changing ocean chemistry could reduce the efficacy of calcifying binders. Ultimately, increased rubble cover will negatively impact coral recruitment into rubble beds. Rubble mobilization abrades and smothers corals, and rubble beds typically experience altered environmental and ecological conditions to the coral frameworks that precede them. Several knowledge gaps exist in relation to improved rubble mobilization thresholds, binding rates and strengths, and coral survival in varying rubble bed types and hydrodynamic regimes. Addressing these knowledge gaps will improve our ability to predict the recovery trajectory of rubble beds and assess the need for stabilization interventions.

Phase shift from a stony-coral to a soft-coral community on a coral reef: a case study of an alternative state

ABSTRACT A phase shift from a stony-coral community to an alternative state represented by octocorals and corallimorpharians was recorded on a coral reef at the Hon Noi Islands (offshore area of south-central Vietnam). For a seven-year period, average stony-coral cover decreased from 80% to 4.7%, diversity of reef-building corals decreased from 169 to 17 species, and in the shallow area of a reef (1–4 m depth), the cover of corallimorpharians (mainly Rhodactis indosinensis) and octocorals (mainly Clavularia sp.) increased to 62%. Mass scleractinian mortality could have resulted from an outbreak of crown-of-thorns starfish, Acanthaster sp., which developed in the surrounding area in the last decade. The only significant contributor to stony-coral recovery on the study reef to date was the blue coral, Heliopora coerulea. Given the serious coral decline on the upstream reefs as potential sources for coral recruitment and competitive advantages of corallimorpharians and octocorals over scleractinians, the prospects for rapid scleractinian recovery of the study site are poor.

Engineering, Ecological and Social Monitoring of the Largest Underwater Sculpture in the World at John Brewer Reef, Australia

The largest underwater sculpture in the world, the ‘Coral Greenhouse’ by artist Jason deCaires Taylor, was commissioned by the Museum of Underwater Art and installed at John Brewer Reef, Australia, in December 2019. The planning process required certified engineering design drawings associated with design life, durability and suitability of materials, and baseline ecological surveys. Following approval, the operational phase required annual monitoring of substrate, ecology, social values, and marine debris. We geo-referenced three permanent transects and designed a before/after rapid monitoring assessment of substrate, fish, and invertebrates. Substrate surveys indicated 11% concrete and 89% sand. Fish surveys indicated significant increases of diversity and abundance, with 12 species and 65 individuals recorded in 2018 compared to 46 species and 365 individuals recorded in 2022. Macroinvertebrate species maintained no significant trends in abundance, species richness, and diversity with respect to time between 2018 and 2022. We monitored coral restoration and natural recruitment at the site, measuring aesthetics, survivorship of planted corals, and coral recruitment. Of 131 corals transplanted in March 2020, survivorship was 100% at 1 month, 92% at 6 months, and 91.6% at 12 months. Hard and soft corals were recruited to the structure at a density of 8.35 hard corals/m2 and 10.9 soft corals/m2 over 26 months.

The Long and Winding Road of Coral Reef Recovery in the Anthropocene: A Case Study from Puerto Rico

The persistence and resilience of marginal shallow coral reefs at their limits of environmental tolerance have declined due to chronic environmental degradation and climate change. However, the consequences for the natural recovery ability of reefs of disturbance remain poorly understood. This study considered the potential for natural recovery through coral recruitment on fringing reefs across different geographic regions under contrasting environmental conditions in Puerto Rico. Reefs in areas with significant water quality degradation and more severe physical impacts of hurricanes were expected to have lower coral recruit density and diversity, and therefore less potential for recovery. Sixteen reefs were assessed across three geographic regions. Degraded reefs sustained a lower percentage of live coral cover and had higher macroalgae and turf algae abundance. Locations affected by high PO4, NH3+ and optical brightness concentrations, high turbidity, and high sea surface temperature anomalies, chlorophyll-a concentration and light attenuation Kd490 evidenced significantly lower coral recruit density and diversity. Hurricane-decimated reefs also exhibited impoverished coral recruit assemblages. Low coral recruitment could have important long-term implications under projected climate change and sea level rise, particularly in coastal urban habitats. There is a need to implement effective environmental conservation, ecological restoration and community participation strategies that facilitate enhanced coral recruitment success and assisted recovery processes.