EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 Community of juvenile hard corals (Scleractinia) in different geomorphological type and reef benthic communities M Abrar1*, T A Hadi1, T Handayani1, N P Zamani2, Suharsono1 and D G Bengen2 1 Research Center for Oceanography, Indonesian Institute of Sciences, Indonesia Faculty of Fisheries and Marine Science, IPB University, Indonesia 2 * Email: abrarcoral@gmail.com Abstract. Juvenile corals are an important stage in the life history and demographics of coral populations in nature however, their survival is influenced by the physical environment and benthic coral reef communities. The study of juvenile coral communities with a maximum size of 10 cm on the reefs of Pulau Weh, Sabang, Aceh was conducted to observe juvenile coral communities and determine their relationship with geomorphological types and benthic reefs communities. A total of 9 sites with 72 sampling squares were distributed in different geomorphological; tectonic type with hard substrates of lava and limestone, volcanic type with predominantly sand substrate, and dead coral with algae with the presence of hot springs in the vicinity. In total, we found 25 genera of juvenile corals from 12 families, and the abundance reached 449 colonies with an average of 37.41 colonies per site. The mean density was 6.66 ± 5.99 colonies/m2 (±SD) and varied significantly between sites (p=4.878-7; <0.05), which was dominated by the genera Porites, Pavona, Acropora, Montipora, and Favia. Live coral cover (HC), dead coral algae (DCA), and hard rock substrate (RK) did not affect, however rubble coral (R) was significantly affected (p=1.9-2; <0.05). Geomorphological conditions and benthic reef cover did not show a significant effect (p = 0.48; < 0.05), although juvenile corals were very common and better in the tectonic type than the volcanic type. The survival of juvenile corals was low, where the smaller size was significantly high compared to the larger size (p=4.5-5; <0.05). Our study provides up-to-date information and data on juvenile coral communities based on geomorphological conditions and local benthic reef communities. Keywords: Coral recruitment, juvenile corals, live coral, dead coral with algae, tectonic type, volcanic type, geomorphology 1. Introduction Coral reefs are important in shallow water ecosystems that continue to be degraded due to the accumulation and combination of various threats, including climate change, destructive fishing, pollution, and water quality degradation [1, 2]. The impact of these pressures on coral reefs is variable, with many areas causing reefs to permanently lose their habitat [3] and some reef areas to survive and recover. Naturally, coral reefs under pressure will survive and have the resilience to recover. The resilience ability of coral reefs and indications that the recovery process is in progress can be seen from the occurrence of coral recruitment. The success of coral recruitment is an important ecological process as Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 EMBRIO-2021 IOP Conf. Series: Earth and Environmental Science IOP Publishing 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 a critical point in maintaining and restoring coral communities and coral reefs after experiencing damage [2, 4, 5, 6, 7]. The recruitment of stony corals (Ordo Scleractinia) as the main component of reef building has two phases in its life history, namely the pelagic larval phase and the sessile benthic phase. During the sessile benthic period, coral colony development starts from the recruitment stage of corals measuring <1 cm, then grows into juvenile corals measuring <5 cm and develops into adult corals [8, 9]. It is visually distinguished from its relatively small colony size, which is <5 cm in diameter [8, 9], and several other studies using a size of <10 cm [10]. The sustainability of coral communities is highly dependent on survival after the settlement of coral larvae (post-settlement survivorship), especially at the stages of recruitment and juvenile corals. However, under normal and undisturbed conditions, the process of growth and development and coral mortality is strongly influenced by the structure of the adult corals [7, 9, 11]. Many factors influence the structure and composition of the juvenile corals community, including the geomorphological type and reef topographic [12, 13]. There are two geological factors that play an important role in forming physical contours (profiles) and habitat complexity on coral reefs, and provide local hydrodynamic patterns in the waters. The Geomorphological conditions and reef topography also affect the variation and dominance of benthic communities as a function of habitat suitability and their ecological interactions with juvenile coral communities. The survival and growth of juvenile corals are limited by competition for space with other benthic biotas [14, 15] and predation/grazing by certain biota. Therefore, the combination of geomorphic factors and reef topographic and the form of interaction with the reef benthic communities determines the survival of juvenile corals and provides variations in the recovery process of coral reefs after following damaged [12, 16]. As the center of the world's coral triangle, Indonesia has coasts and many small islands with complete and varied island geomorphological and reef topographic. However, not many studies of coral and juvenile corals on Indonesia's different geological conditions have been carried out. Demographic studies of juvenile corals communities in Seychelles waters on a mixed geomorphological form of granite and carbonate islands with the dominance of different benthic reef communities have shown a relationship with the structure and survival of coral tillers [8]. Geomorphologically, Weh Island, Sabang City, Aceh belong to the category of the hilly island with mountains and steep hills [17, 18]. The geomorphological and topographic conditions of Pulau Weh with a hilly island type with a mixture of tectonic and active volcanoes are thought to affect the shape of the reef habitat and the hydrological conditions. Our study observes the structure and composition of juvenile coral communities and investigates how it relates to the geomorphological type and reef topography. In particular, our study measures the variation of juvenile corals and live coral cover and other benthic reef communities and investigated how they relate to different geomorphological types and reef topography. 2. Materials and methods 2.1. Location Pulau Weh, one of Indonesia's northernmost small islands, is geomorphologically characterized by steep mountains and hills formed by fracture and erosion (figure 1b). The part of Pulau Weh with a stratovolcano type is located in the southeast, formed by andesite and basaltic rocks (58%), clastic volcanic rocks (30%), coral reefs, and alluvium (12%) [19]. The western high topographic area consists of andesite, lava breccia, and sandy tuff lava. In some areas, low relief is found in the north, the port of Sabang, in the northwest and south of the island. On the east side, there is a mountain range stretching from southeast to northwest, which is a reflection morphology of the strike-slip fault of the GSF. While the north-south part is dominated by another morphology indicated by a trending ridge, which is a normal fault [17, 18, 19, 20, 21, 22, 23]. Rocky shores dominate the reef topography with poorly developed reef flats, relatively steep reef slopes composed of hard igneous rock substrate and reef limestone where benthic communities are well developed including hard corals (Scleractinia). 2 EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 b a Figure 1. Map of location and distribution of research sites, Source: COREMAP-CTI LIPI 2018 (a) and map of distribution of geomorphological types of Pulau Weh, Source: Suhanto et al, 2005 (b). Kuadrat 0 meter 10 me 1 9 Foto: Hickerson/FGBNMS 2010 Meteran meteran 40 1 30 3 3 3 70 meter 4 60 6 Foto: Ken Marks 2013 6 7 6 Foto: Abrar 2021 Figure 2. Sampling scheme of juvenile corals using a 1 x 1 meter quadrat transect method with 6 replications. A total of 12 sites were distributed on the western and eastern outer sides (Site of SBGC01, 02, 03, 10, 11, and 12) and the closest side (north side) in the bay and are relatively sheltered (Site of SBGC04, 05, 06, 07, 08, and 09) (figure 1a). Benthic reefs are dominated by dead coral with algae (DCA) with an average cover of 39.39%. The average live coral cover was 32.91% where the outermost reef is relatively higher than the inner side [24]. The distribution pattern of live coral cover above average or close to average is spread on the outermost eastern side of the bay and the outermost western side of the reef. Several natural events and impacts on coral reef damage were recorded in the past decade, including the 1996 earthquake, 2004 earthquake-tsunami, and 2010 coral bleaching, but there were no reports in 20152016 global bleaching [23, 25, 26]. 3 EMBRIO-2021 IOP Conf. Series: Earth and Environmental Science IOP Publishing 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 2.2. Methods Juvenile corals are visually distinguished based on their relatively small colony size, which is <5 cm in diameter [8] and in other studies using a size of <10 cm [10]. In our study, the juvenile corals were limited from the colony's size that could be observed from visible colonies to a maximum 10 cm in diameter [10]. Data recording includes taxa names (up to genus/species level) and juvenile corals colony size (approximately cm), in a 1 x 1 meter square transect [27], 2000 placed on a 70 meter long transect parallel to the shoreline at a depth of 5-10 meters. A total of 6 sampling squares per station were placed at points 0, 10, 30, 40, 60, and 70 meters (figure 2). Juvenile corals that come from fragmentation, fission, colony shrinkage from the parent colony were not recorded in this observation [8, 28]. Data collection of live coral cover and other benthic reef categories along the coral sapling observation area was carried out using the Underwater Photo Transect (UPT) method. A total of 50 photos were taken at a distance of 1 meter along a 50-meter transect parallel to the coastline at a depth of 5-10 meters, then processed using the CPCe Ver 4.2 application with 30 random points per photo [29]. The identification of the geomorphological and topological characteristics of the reef was carried out by direct observation in the field and underwater and adapted to the geomorphological distribution map of Pulau Weh [30] and the Reef Cover Classification developed by the University of Queensland, Australia [31]. Juvenile corals data were processed and analyzed using descriptive statistical analysis covering species richness (genus level) abundance and density. The size class data are grouped into four (4) size classes, namely 1). size <1cm, 2). Size 1-3 cm, 3). Size >3-5 cm, and 4). Size >5-10 cm, of which 5 cm is categorized as juvenile coral and >5-10 cm is categorized as an adult coral [8]. The distribution of density variation and the average size of juvenile coral colonies between sites were analyzed using a one-way Analysis of Variance (ANOVA) at an error level of 5%. The relationship and effect of benthic reef cover on coral seedlings were tested using linear regression. Multivariate principal component analysis (PCA) was used to determine variations in habitat composition and suitability based on geomorphological and reef topographic using Principal Component Analysis with hierarchical clusters in PRIMER software [32]. 3. Results and discussion 3.1. Community of juvenile corals Totally, we found 25 genera of juvenile corals from 12 families, with a range of 6-16 genera and showing variations among sites with a range of 6-16 genera and 4-8 families (figure 3). The presence of juvenile corals at Site SBGC07 was higher than other sites, namely 8 families and 16 genera with an average of 0.64 of the total (about 60% of the total), while the lowest at Site SBGC11 was 4 families and 10 genera with an average of 0.33 and 0.24 (about 30% and 20% of the total). Overall, the species richness of juvenile corals was relatively higher in protected waters within the bay than in the open waters outside the bay and cape areas. However, Site SBGC06 which is in the bay and was relatively more protected shows a lower coral reef species richness and they were similar with sites placed outside of the bay. The presence of juvenile corals from the Genus Acropora, Montipora, Pavona, Porites, and Pocillopora had a higher presence rate than other genera, more than 80%. The composition and species richness of juvenile corals are important as a part of diversity and predicting the dynamics of coral communities on the reefs [12, 33]. We noted that the richness of juvenile corals (genus) in Pulau Weh was quite diverse and showed a higher tendency in protected waters in the bay than more open waters, except for Site SBGC06. Although in general it was not shown a relationship with the type of geomorphological and reef topographic, local conditions such as the presence of fresh water input and sedimentation from river and runoff, and specific reef geomorphologies are selective factors for the diversity of coral recruitment and survival in juvenile stage [12, 34]. Specific local conditions of Site SBGC06, such as fresh water input from some rivers, sedimentation, and volcanic activity of underwater hot springs limited the diversity and survival of juveniles in this site. Likewise at Site SBGC02 where the bottom substrate was dominated by igneous rock and the reef slopes are relatively steep, limiting the success of recruitment and space for juvenile 4 EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 coral development. The composition of adult coral species was not recorded in this study, however the diversity of adult coral communities was predicted to affect the composition of juvenile coral species. In addition, coral parent communities with varied types and patterns of sexual reproduction also contribute to the diversity of juvenile corals. 18 16 Number of genera 14 12 10 8 6 4 2 0 SBGC01 SBGC02 SBGC03 SBGC04 SBGC05 SBGC06 SBGC07 SBGC08 SBGC09 SBGC10 SBGC11 SBGC12 SITES Total families Total genera Avarage of families Average of genera Figure 3. Composition and species richness of juvenile corals at the Pulau Weh, Sabang City, Aceh. Information and data on the composition of juvenile coral species in Indonesian reefs have been limited, and most of them were available up to the genus level [33]. The species richness of juvenile corals was relatively the same as some other tropical areas of Indonesia [35, 36] and relatively different from subtropical areas [12, 33]. The most common and dominant genera of juvenile corals were Acropora, Pocillopora, and Porites. The genus Pavona, which was commonly found as a local specific genus for the open sea of the west coast of Sumatra, while the genus Favia is a group of massive corals with large polyps which are relatively resistant in turbid waters. A total of 8 genera of juvenile corals (at a sampling square of 0.5 x 0.5 meters, juvenile size < 5cm) were found in the waters of Sambangan Island, Karimun Jawa [35], and Southeast Sulawesi 21 genera and 12 families (square 1 x 1 meter, juvenile < 5 cm) [36] and about 75% of their composition is also found in Pulau Weh, Sabang. 3.2. Density of juvenile corals Overall, the total abundance of juvenile corals reached 449 colonies ranging from 12-82 colonies with an average of 37.41 colonies per Site. The mean colony density of juvenile corals was 6.22 colonies/m2 and between Site varied significantly (p-value = 4.878-7, <0.05) where the highest density was found at SGBC07 Site, namely 13.67 ± 5.35 (colony/ m2 ± SD) and the lowest was at SBGS06 Site, namely 2 ± 0.76 (colonies/m2 ± SD). Juvenile corals from the genera Porites, Pavona, Acropora, Montipora, and Favia respectively, had the highest density than other juvenile corals (figure 4). 5 EMBRIO-2021 IOP Publishing 20 18 16 14 12 10 8 6 4 2 0 1033 (2022) 012045 18 a doi:10.1088/1755-1315/1033/1/012045 b 16 Density (col/m2) Density (col/m2) IOP Conf. Series: Earth and Environmental Science 14 12 10 8 6 4 2 0 Genera Sites Figure 4. Density of juvenile corals by sites (a) and in the top 5 juvenile corals (b). The density of juvenile corals serves as a measure and predictor in the early stages of life history and coral population demographics and an indicator of the recovery rate of reefs after damage [8]. The survival of juvenile corals and prediction of supporting factors measure the success of coral recruitment. Our study showed that live coral cover did not show relationships with juvenile corals and showed a negative correlation. Thus we can say that live coral cover was a limiting factor for the success of coral communities. The diversity and cover of live corals reflect supporting factors as a source of larvae in the coral recruitment process. However, high live coral cover is a limiting factor for successful coral recruitment and as space competitors for corals at the juvenile stage. Other reefs benthic such as dead coral cover with algae (DCA) and rock substrate (RK) although they have potential as attachment substrates for coral larvae, our study showed no correlation with juvenile corals density. Dead coral is an open substrate that is immediately covered by the rapid growth of pioneer algae, thus limiting the space for coral larvae to settle and becoming a space competitor for the development of juvenile corals. Likewise, the rock substrate from tectonic activities need a process to become a good substrate for the settlement of coral larvae and the survival of juvenile corals. The results of field observations of rock substrate have a relatively flat surface structure, solid not hollow and generally covered by barnacles, rare living corals are generally encrusting and massive corals. Another condition showed that rubble corals (R) were positively correlated with juvenile corals and showed a significant relationship. The expanse of rubble corals (R) is an open substrate for the settlement of benthos larvae including corals, the hollow structure and association with CCA supports the settlement of coral larvae and survival of juvenile corals. 3.3. Interaction of reef benthics and types of reef geomorphology Juvenile corals density did not show a significant correlation (r2 = 0.04, P value = 0.473) with live coral cover (HC), although it showed a higher trend at low live coral cover (figure 5a). Dead coral with algae (DCA) (r2 = 0.09, P value = 0.892) and rock substrate (RK) (r2 = 0.09, p value = 0.885) also did not show a significant correlation to juvenile corals. and they were shown a negative correlation pattern (figure 5b). On the other hand, rubble corals (R) showed a significant correlation with juvenile corals (r2 = 0.381, p value = 0.019) with a positive correlation pattern (figure 5c). 6 EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 a doi:10.1088/1755-1315/1033/1/012045 b d c Figure 5. Correlation of juvenile corals with live coral cover (HC) (a), rubble corals (R) (b), and dead coral with algae (DCA) (c) and the relationship between its components (PC) (d). Based on the results of the ordination analysis, it showed that the variation in the benthic composition of the reef was divided into 4 clusters. Most of the sites belong to clusters with habitat characteristics dominated by live coral cover (HC) and dead coral with algae (DCA). In this large cluster, Sites of SBGC06, SBGC09, and SBGC11 formed their own cluster due to the similarity of habitat characteristics, namely HC, DCA, and sand cover (S). The Sites of SBGC03 and SBGC05 have moderate habitat characteristics, while SBGC01 Site forms a separate cluster, with habitat characteristics dominated by rock cover (RK = rock) and other associated reef biotas (OT = others) (figure 6). However, the grouping and relationship between the components of rubble did not show a significant correlation (r2 = 0.063, p-value = 0.48, > 0.05), so it can be said that the habitat suitability based on geomorphology and reef topography had no impact on the juvenile corals. Figure 6. Principal Component Analysis (PCA) relationship between site distribution and the suitability of reef benthic and reef geomorphological types to juvenile corals. 7 EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 Types of geomorphology and reef topology provide habitat complexity and affect the variation of the reef benthic communities and the hydrological pattern of waters. We found that juvenile coral densities tended to be higher in protected to semi-protected reef waters within bays and lower in the open sea near cape [13, 37]. The sites were placed on the east side of Pulau Weh, and Site SBGC06, located on the north side of the bay, the density of juvenile corals was relatively lower. These sites were characterized by volcanic activity and influence, including volcanic sandy bottoms [24] and the emergence of hot springs [19, 23]. More specific local can cause low species richness and density of juvenile corals such as at Site SBGC06, even though they were located in protected waters inside the bays. Conditions such as high sedimentation and volcanic activity (hot springs) at the bottom of Site SBGC06 [19, 23] were thought to affect juvenile corals' structure and composition at this site. Likewise at Site SBGC01, which was on the west side with the open sea outside the bay, where the reef habitat is dominated by rock substrate with relatively steep slopes and quite high associations of coral reef biota as competitors and predators of juvenile corals were seen. However, the suitability of the habitat based on the reef substrate category and the interaction form of the benthic reef biota were something that needs to be known in relation to the environment with juvenile corals. The presence of the juvenile corals community at Pulau Weh, Sabang, Aceh, was expected to provide complete information on coral communities the condition and health of coral reefs in Indonesia. Geomorphologically, Pulau Weh is a small island made from active tectonic and volcanic with coastal geological conditions and small islands with bays, straits, and cape [14, 17, 20, 21]. The east and west sides of the island with open waters, the coast is rocky from lava, which is flatter with active tectonic activity, while on the north side the waters are protected inside bays with beaches mixed with rocks and limestone and sandy with volcanic activity more dominant to the east side. Bay areas with protected waters have relatively weak currents and allow local eddy currents to appear, accumulating dissolved particles and micro-biotic components of various plantonic biota, including coral larvae from other waters. However, the bay area with active volcanic activity with the rising of underwater hot springs impacts the success of the settlement of benthic biota, including larvae corals. 3.4. Jevenile corals size class distribution The abundance of juvenile corals was found higher at sizes 1-3 cm and sizes >3-5 cm, respectively 167 colonies and 172 colonies with a mean of 13.93 ± 8.8 (colonies ± SD) and 14.33 ± 9.0 (colonies±SD). The abundance of juvenile corals with a size of < 1 cm was found to be the lowest, namely 20 colonies with a mean of 1.67 S ± 1.5 (colonies ± SD) and then the size of > 5 cm were 90 colonies with a mean of 7.5 ± 4.08 (colonies ± SD). Juvenile corals with a size of <5cm were very dominant compared to those of >5cm (figure 7). Abundance (colony) 200 150 20,05 100 50 79,95 0 <1 cm 1-3 cm >3-5 cm >5-10 cm Size Class Juvenile corals ≤ 5 cm Juvenile corals >5 cm Figure 7. Distribution of juvenile corals abundance by size class. The juvenile corals period is a vulnerable stage and a critical point in the life history of corals. Appropriate habitat suitability such as the availability of hard and stable substrates as well as positive forms of interaction with other reef benthic communities, are important factors in the survival of juvenile corals. Size class of juvenile corals describes the period of growth and development into adults and 8 EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science 1033 (2022) 012045 doi:10.1088/1755-1315/1033/1/012045 indicates different generations as a form of temporal variation and seasonal patterns of coral reproduction. Changes or the portion of the juvenile corals colony size can be used to determine the survival rate of juvenile corals. Our observations showed that juvenile corals were relatively high in size >1-3 cm and >35 cm. This indicates that the juvenile corals in this size range were relatively stable with a high survival rate, however the size of juvenile corals >5-10 cm indicates a lower, indicating the low survival rate of juvenile corals into mature corals. In other conditions, juvenile corals with a size of <1 cm were seen as low, this illustrates the critical period after larval settlement and development into juvenile corals. The decline in the survival rate of coral juveniles from juvenile to adult was quite significant, however in this study the distribution of juvenile corals size class was not measured based on its relationship to the type of reef geomorphological and reef benthic. The juvenile corals community was quite diverse and varied and showed a relationship with the local conditions of benthic reefs, although the reef's overall geomorphological type and topographic cannot be seen. The distribution of juvenile corals tended to be better at the medium category with live and dead coral cover and supported by high rubble corals cover, as well as the combination of rocks and limestone substrates showed a better juvenile coral. The survival rate of juvenile corals to become adult corals have been low and there was a vulnerable period when they have recruited into juvenile corals. Aknowledgement Our study is part of reef health monitoring and related ecosystems at Pulau Weh, Sabang, Aceh have been supported and funded by the COREMAP-CTI LIPI 2021 Program. This monitoring is also part of my dissertation study at the Doctoral Program in Marine Science, Faculty of Fisheries and Marine Sciences, IPB University. Appendices Annex 1. Richness of juvenile corals genera at Pulau Weh, Sabang, Aceh. TAXA 01 02 03 04 05 + + + + + + + + + SITE SBGC 06 07 08 09 10 11 12 + + + + + + + + + + + Acroproidae 1 2 3 Acropora Astreopora Montipora + + + + + + + + Astrocoeniidae Stylocoeniella armata Agariciidae 4 5 Coeloseris 6 Gardinoseris 7 Leptoseris 8 Pavona Faviidae 9 Cyphastrea 10 Favia 11 Favites 12 Goniastrea 13 Leptastrea 14 Montastrea 15 Platygyra Fungiidae 16 Fungia 17 Podabcia + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 9 + + + + + + + + EMBRIO-2021 IOP Publishing IOP Conf. Series: Earth and Environmental Science TAXA Merulinidae 18 Hydnopora Mussidae 19 Achantastrea Oculinidae 20 Galaxea Pectinidae 21 Pectinia Pocilloporidae 22 Pocillopora 23 Seriatopora Porotidae 24 Porites Siderasteridae 25 Psamocora 01 02 1033 (2022) 012045 03 04 05 + doi:10.1088/1755-1315/1033/1/012045 SITE SBGC 06 07 08 09 + 10 11 12 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + References [1] Burke L, Reytar K, Spalding M and Perry A 2011 Reefs at Risk Revisited (World Resources Institute 2011) [2] Hughes T P, Kerry J T, Baird A H, Connolly S R, Chase T J, Dietzel A, Hill T, Hoey A S, Hoogenboom M O, Jacobson M, Kerswell A, Madin J S, Mieog A, Paley A S, Pratchett M S, Torda G and Woods R M 2019 Global warming impairs stock-recruitment dynamics of corals Nature 568(7752) 387-390 (doi: 10.1038/s41586-019-1081-y) [3] Eakin C M, Sweatman H P A and Brainard R E 2019 The 2014–2017 global-scale coral bleaching event: insights and impacts Coral Reefs 38 539–45 [4] Ritson-Williams R, Arnold S N, Fogarty N D, Steneck R S, Vermeij M J A and Paul V J 2009 New perspectives on ecological mechanisms affecting coral recruitment on reefs Smithson Contrib Mar. 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Freshw. Ecosyst. (DOI: 10.1002/aqc.2464) 12 Reproduced with permission of copyright owner. Further reproduction prohibited without permission.