Gene Flow and Genetic Diversity of a Broadcast-Spawning Coral in Northern Peripheral Populations

Recently, reef-building coral populations have been decreasing worldwide due to various disturbances. Population genetic studies are helpful for estimating the genetic connectivity among populations of marine sessile organisms with metapopulation structures such as corals. Moreover, the relationship between latitude and genetic diversity is informative when evaluating the fragility of populations. In this study, using highly variable markers, we examined the population genetics of the broadcast-spawning coral Acropora digitifera at 19 sites in seven regions along the 1,000 km long island chain of Nansei Islands, Japan. This area includes both subtropical and temperate habitats. Thus, the coral populations around the Nansei Islands in Japan are northern peripheral populations that would be subjected to environmental stresses different from those in tropical areas. The existence of high genetic connectivity across this large geographic area was suggested for all sites (F _ST≤0.033) although small but significant genetic differentiation was detected among populations in geographically close sites and regions. In addition, A. digitifera appears to be distributed throughout the Nansei Islands without losing genetic diversity. Therefore, A. digitifera populations in the Nansei Islands may be able to recover relatively rapidly even when high disturbances of coral communities occur locally if populations on other reefs are properly maintained.     

Genetic differentiation and connectivity of morphological types of the broadcast‐spawning coral Galaxea fascicularis in the Nansei Islands,Japan

Population connectivity resulting from larval dispersal is essential for the maintenance or recovery of populations in marine ecosystems, including coral reefs. Studies of species diversity and genetic connectivity within species are essential for the conservation of corals and coral reef ecosystems. We analyzed mitochondrial DNA sequence types and microsatellite genotypes of the broadcast‐spawning coral, Galaxea fascicularis, from four regions in the subtropical Nansei Islands in the northwestern Pacific Ocean. Two types (soft and hard types) of nematocyst morphology are known in G. fascicularis and are significantly correlated with the length of a mitochondrial DNA noncoding sequence (soft type: mt‐L; hard type: mt‐S type). Using microsatellites, significant genetic differentiation was detected between the mitochondrial DNA sequence types in all regions. We also found a third genetic cluster (mt‐L+), and this unexpected type may be a cryptic species of Galaxea. High clonal diversity was detected in both mt‐L and mt‐S types. Significant genetic differentiation, which was found among regions within a given type (F _ST = 0.009–0.024, all Ps ≤ 0.005 in mt‐L; 0.009–0.032, all Ps ≤ 0.01 in mt‐S), may result from the shorter larval development than in other broadcast‐spawning corals, such as the genus Acropora. Nevertheless, intraspecific genetic diversity and connectivity have been maintained, and with both sexual and asexual reproduction, this species appears to have a potential for the recovery of populations after disturbance.     

Genetic differentiation in Elaeocarpus photiniifolia (Elaeocarpaceae) associated with geographic distribution and habitat variation in the Bonin (Ogasawara) Islands

Gene flow between populations in different environmental conditions can be limited due to divergent natural selection, thus promoting genetic differentiation. Elaeocarpus photiniifolia, an endemic tree species in the Bonin Islands, is distributed in two types of habitats, dry scrubs and mesic forests. We aim to elucidate the genetic differentiation in E. photiniifolia within and between islands and between the habitat types. We investigated genotypes of 639 individuals from 19 populations of E. photiniifolia and its closely-related E. sylvestris at 24 microsatellite loci derived from expressed sequence tags. The data revealed genetic differentiation (1) between E. photiniifolia and E. sylvestris (0.307 ≤ F _ST ≤ 0.470), (2) between the E. photiniifolia populations of the Chichijima and Hahajima Island Groups in the Bonin Islands (0.033 ≤ F _ST ≤ 0.121) and (3) between E. photiniifolia populations associated with dry scrubs and mesic forests in the Chichijima Island Group (0.005 ≤ F _ST ≤ 0.071). Principal coordinate analysis and Bayesian clustering analysis also showed that genetically distinct groups were associated with the habitat types, and isolation by distance was not responsible for the genetic differentiation. These findings suggest that E. photiniifolia is divided into genetically differentiated groups associated with different environmental conditions in the Bonin Islands.     

Unexpectedly complex gradation of coral population structure in the Nansei Islands,Japan

To establish effective locations and sizes of potential protected areas for reef ecosystems, detailed information about source and sink relationships between populations is critical, especially in archipelagic regions. Therefore, we assessed population structure and genetic diversity of Acropora tenuis, one of the dominant stony coral species in the Pacific, using 13 microsatellite markers to investigate 298 colonies from 15 locations across the Nansei Islands in southwestern Japan. Genetic diversity was not significant among sampling locations, even in possibly peripheral locations. In addition, our results showed that there are at least two populations of A. tenuis in the study area. The level of genetic differentiation between these populations was relatively low, but significant between many pairs of sampling locations. Directions of gene flow, which were estimated using a coalescence‐based approach, suggest that gene flow not only occurs from south to north, but also from north to south in various locations. Consequently, the Yaeyama Islands and the Amami Islands are potential northern and southern sources of corals. On the other hand, the Miyako Islands and west central Okinawa Island are potential sink populations. The Kerama Islands and the vicinity of Taketomi Island are potential contact points of genetic subdivision of coral populations in the Nansei Islands. We found that genetic population structure of A. tenuis in the Nansei Islands is more complex than previously thought. These cryptic populations are very important for preserving genetic diversity and should be maintained.     

Genetic structure of the critically endangered Red‐headed Wood Pigeon Columba janthina nitens and its implications for the management of threatened island populations

The Red‐headed Wood Pigeon Columba janthina nitens is endemic to the Ogasawara Islands, an oceanic island chain located 1000 km south of the main islands of Japan. The subspecies is at high risk of extinction because of its small population size and restricted habitat range. We undertook genetic analyses of this pigeon using sequences of a portion of the mitochondrial control region and five microsatellite markers to estimate the genetic characteristics of two wild populations from the Bonin and Volcano Islands, as well as one captive breeding population. The genetic diversity of the wild individuals was exceptionally low in both the mitochondria (nucleotide diversity = 0.00105) and at the microsatellite (3.2 alleles per locus and H_E = 0.12) loci. Higher numbers of microsatellite genotypes were observed in the Volcano Islands population than in the Bonin Islands population, which may be because of the relatively low impact of human disturbance. The most common mitochondrial haplotypes and microsatellite alleles observed in the two wild populations were completely fixed in the captive population. Our results suggest that the genetic diversity of the captive population needs to be increased. However, introduction of a wild individual into a captive population can lead to a decreased genetic diversity in the wild population and therefore should be done with caution. The genetic differentiation between the Bonin and the Volcano island groups was low, and the populations of the two island groups should be regarded as a single evolutionarily significant unit. However, special consideration is required for habitat conservation in the Volcano Islands, which may be functioning as a sanctuary for the Red‐headed Wood Pigeon. For the long‐term conservation of threatened bird species that live on remote oceanic islands, determination of management units considering gene flow caused by their flying capacity and maintenance of genetically suitable wild and captive populations are essential.     

Molecular Evidence Shows Low Species Diversity of Coral-Associated Hydroids in Acropora Corals

A novel symbiosis between scleractinians and hydroids (Zanclea spp.) was recently discovered using taxonomic approaches for hydroid species identification. In this study, we address the question whether this is a species-specific symbiosis or a cosmopolitan association between Zanclea and its coral hosts. Three molecular markers, including mitochondrial 16S and nuclear 28S ribosomal genes, and internal transcribed spacer (ITS), were utilized to examine the existence of Zanclea species from 14 Acropora species and 4 other Acroporidae genera including 142 coral samples collected from reefs in Kenting and the Penghu Islands, Taiwan, Togian Island, Indonesia, and Osprey Reef and Orpheus Island on the Great Barrier Reef, Australia. Molecular phylogenetic analyses of the 16S and 28S genes showed that Acropora-associated Zanclea was monophyletic, but the genus Zanclea was not. Analysis of the ITS, and 16S and 28S genes showed either identical or extremely low genetic diversity (with mean pairwise distances of 0.009 and 0.006 base substitutions per site for the 16S and 28S genes, respectively) among Zanclea spp. collected from diverse Acropora hosts in different geographic locations, suggesting that a cosmopolitan and probably genus-specific association occurs between Zanclea hydroids and their coral hosts.     

Genetic Differentiation and Spatial Structure of Phellinus noxius,the Causal Agent of Brown Root Rot of Woody Plants in Japan

Phellinus noxius is a pathogenic fungus that causes brown root rot disease in a variety of tree species. This fungus is distributed in tropical and sub-tropical regions of Southeast and East Asia, Oceania, Australia, Central America and Africa. In Japan, it was first discovered on Ishigaki Island in Okinawa Prefecture in 1988; since then, it has been found on several of the Ryukyu Islands. Recently, this fungus was identified from the Ogasawara (Bonin) Islands, where it has killed trees, including rare endemic tree species. For effective control or quarantine methods, it is important to clarify whether the Japanese populations of P. noxius are indigenous to the area or if they have been introduced from other areas. We developed 20 microsatellite markers from genome assembly of P. noxius and genotyped 128 isolates from 12 of the Ryukyu Islands and 3 of the Ogasawara Islands. All isolates had unique genotypes, indicating that basidiospore infection is a primary dissemination method for the formation of new disease foci. Genetic structure analyses strongly supported genetic differentiation between the Ryukyu populations and the Ogasawara populations of P. noxius. High polymorphism of microsatellite loci suggests that Japanese populations are indigenous or were introduced a very long time ago. We discuss differences in invasion patterns between the Ryukyu Islands and the Ogasawara Islands.     

Regional genetic differentiation among populations of Cladocora caespitosa in the Western Mediterranean

Cladocora caespitosa is the only reef-forming zooxanthellate scleractinian in the Mediterranean Sea. This endemic coral has suffered severe mortality events at different Mediterranean sites owing to anomalous summer heat waves related to global climate change. In this study, we assessed genetic structure and gene flow among four populations of this species in the Western Mediterranean Sea: Cape Palos (SE Spain), Cala Galdana (Balearic Islands), Columbretes Islands, and L’Ametlla (NE Spain). The results obtained from Bayesian approaches, F _ST statistics, and Bayesian analysis of migration rates suggest certain levels of genetic differentiation driven by high levels of self-recruitment, a fact that is supported by egg-retention mechanisms. Conversely, genetic connectivity among distant populations, even if generally low, seems to be related to sporadic dispersal events through regional surface currents linked to the spawning period that occurs at the end of summer-beginning of autumn. These features, together with a certain isolation of the Columbretes Islands, could explain the regional genetic differentiation found among populations. These results help to better understand population structure and connectivity of the species and will serve as an approach for further studies on different aspects of the biology and ecology of C. caespitosa.     

Genetic variation of pantropical Terminalia catappa plants with sea‐drifted seeds in the Bonin Islands: suggestions for transplantation guidelines

The Bonin Islands are endowed with endemic species. However, these species are at risk of extinction because of the exuberance of invasive alien plants. Therefore, native plant species should be revegetated after eradicating alien plants. We investigated the genetic variation of Terminalia catappa populations in the Bonin Islands by using nuclear (n) microsatellites (simple sequence repeats [SSRs]) and chloroplast (cp) DNA. No significant differences were observed in the genetic diversity of nSSRs among 22 populations. However, recent bottlenecks were detected in three populations on the Chichijima Island group. nSSR variation and cpDNA haplotypes suggested the presence of two genetically distinct groups in the Mukojima and Chichijima Island groups and the Hahajima Island group. A similar genetic structure was observed in plants and animals in the Bonin Islands. Populations on the three islands, which were separated from other islands in each island group when the water depth was 50‐m lower than the present level, were dominated by unique nSSRs clusters, suggesting that historical changes in island connections during the Pleistocene era affected genetic substructuring. These results suggested that different factors contributed to the genetic structure of T. catappa on different geographic scales. At the whole‐island level, the genetic structure was determined by long‐distance seed dispersal by ocean currents. At the island‐group level, the genetic structure was determined by historical changes in island connections caused by changes in the sea level due to glacial–interglacial transition. These findings would help in establishing transplantation zone borders for revegetating T. catappa on the Bonin Islands.     

Distyly and incompatibility in Psychotria homalosperma (Rubiaceae), an endemic plant of the oceanic Bonin (Ogasawara) Islands

Distyly rarely occurs on oceanic islands. Indeed, this form of polymorphism is absent on the Hawaiian Islands and in New Zealand. However, Psychotria homalosperma (Rubiaceae), which is endemic to the oceanic Bonin Islands of Japan, was presumed to maintain a distylous breeding system and floral morphology. We investigated the floral and reproductive characteristics of this species and examined incompatibility in self- and intramorph pollination. Psychotria homalosperma is morphologically and functionally distylous, based on findings with the examined populations, but its stigma and anther heights are not exactly reciprocal between the two morphs. This is the second example of distyly among the flora from the Bonin Islands, the other being the endemic P. boninensis. Both of these distylous species contrast with the Hawaiian Psychotria species, which have already become dioecious. The flowers of the long (L)-styled (pin) morph of the Bonin Islands plants are completely self- and intramorph incompatible, while the flowers of the short (S)-styled (thrum) morphs are partially intramorph compatible. The S-styled morph was more abundant in the examined populations from three islands of the archipelago, probably due to the existence of partial S–S intramorph compatibility.     

Tectonic subsidence provides insight into possible coral reef futures under rapid sea-level rise

Sea-level rise will change environmental conditions on coral reef flats, which comprise extensive habitats in shallow tropical seas and support a wealth of ecosystem services. Rapid relative sea-level rise of 0.6 m over a relatively pristine coral reef in Solomon Islands, caused by a subduction earthquake in April 2007, generated a unique opportunity to examine in situ coral reef response to relative sea-level rise of the magnitude (but not the rate) anticipated by 2100. Extent of live coral was measured from satellite imagery in 2003, 2006, 2009 and 2012. Ecological data were obtained from microatolls and ecological surveys in May 2013. The reef was sampled at 12 locations where dense live hard coral remained absent, remained present or changed from absent to present following subsidence. Ecological data (substratum depth, live coral canopy depth, coral canopy height, substratum suitability, recruitment, diversity and Acropora presence) were measured at each location to identify factors associated with coral response to relative sea-level rise. Vertical and horizontal proliferation of coral occurred following subsidence. Lateral expansion of live coral, accomplished primarily by branching Acropora spp., resulted in lower diversity in regions which changed composition from pavement to dense live coral following subsidence. Of the ecological factors measured, biotic factors were more influential than abiotic factors; species identity was the most important factor in determining which regions of the reef responded to rapid sea-level rise. On relatively pristine reef flats under present climatic conditions, rapid relative sea-level rise generated an opportunity for hard coral to proliferate. However, the species assemblage of the existing reef was important in determining response to sea-level change, by providing previously bare substrate with a source of new coral colonies. Degraded reefs with altered species composition and slower coral growth rates may be less able to respond to climate change-induced sea-level changes.     

Recruitment and larval connectivity of a remnant Acropora community in the Arabian Gulf,United Arab Emirates

Coral cover and community structure in the Arabian Gulf have changed considerably in recent decades. Recurrent bleaching events have dramatically reduced the abundance of previously dominant Acropora corals and have given space to other more thermally resistant coral taxa. The loss of Acropora spp. has reduced reef structural complexity and associated biodiversity. Sir Bu Nair Island (SBN) is a nature reserve in the United Arab Emirates that sustains some of the last dense and extensive Acropora stands in the southern Gulf. This study investigated coral recruitment at a southern coral reef on SBN and examined larval dispersal and reef connectivity between SBN and other local and regional reefs through an agent-based model coupled with a 3D hydrodynamic model. Recruitment was surveyed with settlement tiles deployed from April to September 2019. Contrary to other reefs in the Gulf, we found that Acropora is indeed the major coral recruiter settling at SBN reefs, followed by Porites. The models indicate that SBN reefs are mostly self-seeding but also connected to other reefs in the Gulf. SBN can supply coral larvae to the neighbouring islands Siri and Abu Musa, and nearby reefs along with the north-eastern Emirates, Iranian coast and Strait of Hormuz. Findings highlight the importance of SBN to protect remnant populations of the locally almost extinct Acropora in a region where natural coral recovery is increasingly sparse.

     

Genetic Diversity and Connectivity in the Threatened Staghorn Coral (Acropora cervicornis) in Florida

Over the past three decades, populations of the dominant shallow water Caribbean corals, Acropora cervicornis and A. palmata, have been devastated by white-band disease (WBD), resulting in the listing of both species as threatened under the U.S. Endangered Species Act. A key to conserving these threatened corals is understanding how their populations are genetically interconnected throughout the greater Caribbean. Genetic research has demonstrated that gene flow is regionally restricted across the Caribbean in both species. Yet, despite being an important site of coral reef research, little genetic data has been available for the Florida Acropora, especially for the staghorn coral, A. cervicornis. In this study, we present new mitochondrial DNA sequence data from 52 A. cervicornis individuals from 22 sites spread across the upper and lower Florida Keys, which suggest that Florida''s A. cervicornis populations are highly genetically interconnected (F_ST = −0.081). Comparison between Florida and existing mtDNA data from six regional Caribbean populations indicates that Florida possesses high levels of standing genetic diversity (h = 0.824) relative to the rest of the greater Caribbean (h = 0.701±0.043). We find that the contemporary level of gene flow across the greater Caribbean, including Florida, is restricted ( = 0.117), but evidence from shared haplotypes suggests the Western Caribbean has historically been a source of genetic variation for Florida. Despite the current patchiness of A. cervicornis in Florida, the relatively high genetic diversity and connectivity within Florida suggest that this population may have sufficient genetic variation to be viable and resilient to environmental perturbation and disease. Limited genetic exchange across regional populations of the greater Caribbean, including Florida, indicates that conservation efforts for A. cervicornis should focus on maintaining and managing populations locally rather than relying on larval inputs from elsewhere.     

Cryptic genetic divergence within threatened species of <Emphasis Type="Italic">Acropora</Emphasis> coral from the Indian and Pacific Oceans

Most hard corals have broad distributions, and historically this was attributed to their capability for extensive dispersal leading to high evolutionary and demographic inter-dependence among regions. More recently there has been a paradigm shift in the understanding of coral dispersal, driven largely by genetic evidence, which has put greater emphasis on self-recruitment and larval retention. There is now a growing body of evidence that morphologically cryptic species exist within many recognized ‘species’ of stony corals. Here, we characterise levels of genetic divergence within and between five species of Acropora sampled from disparate populations spanning the Indo-Pacific Oceans. We find that strong regional genetic differentiation corresponding to the separation of the Indian and Pacific Ocean basins is a consistent pattern in three of the five species examined. Furthermore, the extent of allopatric divergence within species is similar to that observed between species, implying negligible contemporary gene flow between regions in four of the five species examined. This is consistent with the presence of numerous morphologically cryptic allopatric subspecies or incipient Acropora species. If this is confirmed, the conservation status of several species, which are already demonstrably threatened, would require re-evaluation so that risks including silent extinctions and inappropriate translocations are properly managed.     

Predicting Coral Recruitment in Palau’s Complex Reef Archipelago

Reproduction and recruitment are key processes that replenish marine populations. Here we use the Palau archipelago, in the western Pacific Ocean, as a case study to examine scales of connectivity and to determine whether an oceanographic model, incorporating the complex reef architecture, is a useful predictor of coral recruitment. We tested the hypothesis that the reefs with the highest retention also had the highest densities of juvenile coral density from 80 field sites. Field comparisons showed a significant correlation between the densities of juvenile Acropora colonies and total larval recruitment derived from the model (i.e., calculated as the sum of the densities of larvae that self-seeded and recruited from the other reefs in the archipelago). Long-distance larval imports may be too infrequent to sustain coral populations, but are critical for recovery in times of extreme local stress.     

Disappearance of <Emphasis Type="Italic">Acropora</Emphasis> from the Marquesas (French Polynesia) during the last deglacial period

The major reef-building coral genus Acropora has never been recorded, living or fossil, from the Marquesas Islands in the central Pacific Ocean, which are characterized by limited modern reef formations. During the “Musorstom 9” cruise in 1997, investigations of marine platforms representing drowned reef systems revealed for the first time the presence of two Acropora species as fossils at seven Marquesas islands. The predominant species was Acropora valida, which was widespread in the archipelago and dated between 7.4 and 48.6 ka, providing evidence of an earlier Pacific distribution pattern broader than previously observed. It is proposed that disappearance of Acropora after 7.4 ka was linked to climatic events probably ENSO events controlling the distribution of corals and coral reefs in the eastern Pacific without excluding alternatively the effects of an increase in sea-level rise.     

Ecological and genetic differentiation in Persea boninensis (Lauraceae) endemic to the Bonin (Ogasawara) Islands

Persea boninensis (Lauraceae) is an endemic tree species distributed throughout the Bonin Islands. It grows in a wide range of environments from dry to mesic forests, and has multiple flowering peaks that may correspond to different habitats on Chichijima Island of the Bonin Islands. We predicted that P. boninensis is differentiated into two groups with different habitats on these islands. We examined and compared the flowering phenology, morphology, and genetics of populations of species growing in dry and mesic forests. We also performed preliminary artificial crossing experiments. Based on our results, P. boninensis on the Chichijima Islands can be clearly divided into two genetic groups with different habitats and flowering times. Although the flowering time difference could act as an effective pre‐zygotic isolation mechanism between the two groups, there was still a 1‐month overlap in flowering time. Furthermore, our artificial crossing experiments between the two groups resulted in plants that set seeds. Therefore, there was no evidence of reproductive isolation after fertilization. Differences in flowering time as well as in growth habitat will have to occur to maintain genetic differentiation between the two groups of P. boninensis.     

Feeding behavior and diet of the eight-banded butterflyfish Chaetodon octofasciatus in the Thousand Islands,Indonesia

Marine fishes reach their highest diversity in coral reef ecosystems, which they utilize as territory, place of refuge and reproduction, and source of food. One type of predation among reef fishes is feeding on coral polyps, and a single, easily identifiable family of fishes, Chaetodontidae, contains the majority of obligate corallivore species. Multiple studies have examined the behaviour and ecology of Chaetodontidae and their relationship with the benthic habitat. However, many questions remain about their feeding ecology and food specifity at the species level. The present study is the first attempt to systematically decipher the feeding behavior of the obligate corallivore, Chaetodon octofasciatus. Field data were collected from four sites in the Thousand Islands, Indonesia, during two sampling campaigns in 2006, covering two seasons and two different depths. A high abundance of C. octofasciatus was positively related to hard coral cover. Out of a total of 57 scleractinian coral genera observed during the study period, 24 were utilized by C. octofasciatus. All fish collected during the study (n?=?36) had >86 % nematocysts in their guts, supporting their classification as obligate corallivores. Based on the Strauss electivity index, C. octofasciatus displayed a preference for the coral genus Acropora at all depths, while preference for Fungia became more marked at greater depth. Both Acropora and Fungia were observed at high density at all sites, with Acropora density decreasing markedly with depth and Fungia density increasing. Bite rates showed an asymptotic relationship to Acropora density, levelling off between 15 and 20 bites/5 min. The existence of a strong relationship with live coral cover and the preference for specific genera such as Acropora designate C. octofasciatus as a potential bioindicator in the Thousand Islands reefs, while making it particular susceptible to the ongoing degradation of reefs in the region.     

Lecanicillium primulinum,a new hyphomycete (Cordycipitaceae) from soils in the Okinawa's main island and the Bonin Islands,Japan

Lecanicillium primulinum, a new hyphomycete classified in the Cordycipitaceae (Hypocreales, Ascomycota), was isolated from soils collected from the Okinawa's main island and the Bonin Islands, Japan. Using a combination of micro-morphological characteristics and sequences of the ribosomal RNA genes and ITS regions, the isolates were identified as a species of Lecanicillium which was previously undescribed. Phylogenetically the species is close to L. acerosum and Lecanicillium sp. 1 and morphologically it is similar to L. longisporum, L. psalliotae and Lecanicillium sp. 1, but its microconidia differ and it is clearly separated phylogenetically.     

Genetic relationships of the hydrocoral Millepora alcicornis and its symbionts within and between locations across the Atlantic

Although the hydrocoral Millepora alcicornis is a prominent and ecologically relevant amphi-Atlantic reef builder, little attention has been given to its endosymbionts which are also involved in the survival and adaptation success of the species in different environments. In this study, we resolve the genetic relationships between M. alcicornis and its symbionts (Symbiodiniaceae) within both sides and across the Atlantic. The COI and 16S-rDNA regions were selected for the host tissues, and the 23S-rDNA and ITS regions were chosen for the symbionts. Phylogenetic networks consistently showed that host populations from the eastern Atlantic archipelagos (Canary and Cape Verde Islands) were more related to western Atlantic populations than they were between them. However, results for Symbiodiniaceae species varied according to the molecular marker used. Samples from Mexico were grouped as Symbiodinium sp. (formerly Symbiodinium clade A) by both markers. Specimens from Puerto Rico were grouped as either Symbiodinium sp. or Breviolum sp. (formerly Symbiodinium clade B), according to the molecular marker used. Most samples from the eastern Atlantic were identified as Breviolum sp. by both markers, except for one sample from the Canary Islands and two samples from the Cape Verde Islands, which were identified as Cladocopium sp. (formerly Symbiodinium clade C) using ITS-rDNA. These results suggest that these two genera of Symbiodiniaceae may cohabit the same M. alcicornis colony. Because hydrocorals from the Canary Islands were phylogenetically related to the western Atlantic, but symbionts were more related to those of the Cape Verde Islands, the origin of the coral and its symbionts is probably different. This may be explained either by “horizontal” transmission, i.e. acquisition from the environment, or by a change in the dominant symbiont composition within the host. The flexibility of this hydrocoral to select symbionts, depending on environmental conditions, can provide new insight to understand how this coral may face ongoing climate change.