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Photographs of Caribbean candelabrum corals in situ. A, Eunicea pinta Bayer & Deichmann Roncador Bank Colombia, 25 m; B, Eunicea palmeri Bayer, Roncador Bank, Colombia, 12 m; C, Eunicea succinea (Pallas) Bocas del Toro, Panama, 12 m; D, Eunicea laxispica (Lamarck), fore-reef terrace, 20 m, Abaco, Bahamas (2000); E, Eunicea mammosa Lamouroux, Roncador Bank, Colombia, 12 m; F, Eunicea tourneforti Milne Edwards & Haime, Carrie Bow Cay, Belize, 8 m; G, Eunicea asperula Milne-Edwards & Haime, outer slope edge, Cat island, Bahamas (2001); H, Eunicea laciniata Duchassaing & Michelotti, shallow fore-reef, 10 m, Carrie Bow Cay, Belize (2001); I, Eunicea fusca Duchassaing & Michelotti, White Horse Reef, fore-reef, 20 m, Exuma Cays, Bahamas (2000).
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Candelabrum gorgonian corals (genus Eunicea Lamouroux, 1816), with 15 valid species, comprise the most diverse
and abundant group of octocorals in Caribbean coral reefs. The systematics of Eunicea was estimated based on 17
discrete morphological characters, mostly from sclerite morphology. Club sclerites, found on the surface of
gorgonian tissue, p...
Contexts in source publication
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... features: The anthocodial sclerites are flat rods of several sizes with some deformations. These rods are placed either on the base of the polyp or on the tentacles (Bayer, 1961). Description: Colonies up to 1 m in height but usually shorter than 60 cm. External coloration ochre (Fig. 1B). Branching pattern variable from candela- brum to bushy. Some colonies with enlarged and poorly ramified branches. Terminal branches approxi- mately 0.7 mm in diameter. Sclerites from the middle layer enlarged, and having transparent spindles up to 2 mm in length, usually thin 0.09-0.2 mm wide. Purple spindles between 0.13 and 0.5 mm ...
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... exposure on reef terraces and slopes. Scale of calyx low < ring < lip < long lip < long, low is near absent and long is up to 10 mm and usually tubular, lip is when the lower part is longer than the upper, and ring is low but uniform. Description: Colonies up to 30 cm in height, branching mainly in one plane; branches long but scarcely branched ( Fig. 1D). Dry colonies beige to pale ochre. Sclerites from middle layer large and acute; spindles up to 1.5 mm. Axial layer sclerites variable in size and form; acute spindles or short spindles with prominent ornamentation (Fig. 2Q). Polyp rods flattened. Surface sclerites torch-like clubs ( Fig. ...
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... features: Middle layer spindles observed under light microscope with a nontranslucent dark (black, purple, or brown) internal core and transpar- ent periphery or warts. (Fig. 1F). Calyx with prominent inferior lip and ascendant, sometimes covers upper lip. Middle layer with large and stout spindles up to 2 mm length and 0.38 mm width (3.5 times longer than wider). ...
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... material: ICN-MHN-CO-086 (E-89), Albu- querque Cays (12° 10′ 36″N, 81° 51′ 05″W), San Andrés and Providencia archipelago, Colombian Car- ibbean, col. J.A. Sánchez, vi.1994 Description: Colonies up to 1 m in height, either candelabrum-like or with a few long branches (Fig. 1G). Terminal branches usually 5 to 10 mm in diameter. Dry colonies deep black. Calyx with a small projecting lower lip and paler in respect to the sur- rounding tissue in dry samples. Middle layer sclerites spindles between 0.69 and 1.9 mm in length. Polyp armature of long and curved rods (0.45-0.55 mm in length), medium sized ones ...
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... Colony base either a hold fast or a basal stolon with horizontal propagation; branch fragmen- tation and reattachment observed (Fig. 1H). Calyx aperture conspicuous with eight surrounding lobules and projecting lower lip, sometimes covering the upper lip. Middle layer with diverse forms of spindles usually between 0.5 and 1.7 mm in length (Fig. 2B). Axial layer sclerites ornate spindles colourless or pale violet. Polyp armature of rods between 0.05 and 0.2 mm in length. ...
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... features: Colonies up to 0.8 m with thick round branches (10-18 mm in diameter), which usually are unbranched because the base and their branch tip are enlarged (clavate; Fig. 1H). Asexual propagation through fallen stolon-like branches com- monly ...
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... Colonies usually small (< 0.3 m) but up to 0.5 m in height. Asexual (vegetative) propagation from fragments commonly observed (Fig. 1I). Colony with disorganized branching but with a dichotomous trend. Slim branches between 2.5 and 3.5 mm in diameter. Polyp apertures with low calyx as an enlargement of the lower lip. Middle layer with spindle sclerites up to 2 mm in length. Axial layer sclerites spindles up to 0.2 mm in length colourless or slightly violet, sometimes ...
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... and 30 m in depth. Description: Colonies tall and bushy up to 1.3 m in height. Thin branches 3-5 mm in diameter or less at the branch tips (Fig. 9). Small and brown (probably because of zooxanthellae) polyps. Numerous low calyces disposed uniformly with a projecting lower tip. Middle layer sclerites blunt and usually with less than 1 mm in length (Fig. 10A-D). A clear dark core in the sclerite noted under the light microscope. Axial layer composed of a diverse array of ornate forms of capstans and spindles usually purple-coloured and up to 0.11-0.17 mm in length (Fig. 11E). Polyp armature composed of ornate sclerites (0.14-0.32 mm in length) as well as little flat rods (0.06-0.12 mm; e.g. ...
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... calyces disposed uniformly with a projecting lower tip. Middle layer sclerites blunt and usually with less than 1 mm in length (Fig. 10A-D). A clear dark core in the sclerite noted under the light microscope. Axial layer composed of a diverse array of ornate forms of capstans and spindles usually purple-coloured and up to 0.11-0.17 mm in length (Fig. 11E). Polyp armature composed of ornate sclerites (0.14-0.32 mm in length) as well as little flat rods (0.06-0.12 mm; e.g. Fig. 11D). The surface layer contains tiny club scler- ites (foliate to torched) with short handle (Fig. 11A- C), which are the shortest observed amongst Eunicea ...
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... (Fig. 10A-D). A clear dark core in the sclerite noted under the light microscope. Axial layer composed of a diverse array of ornate forms of capstans and spindles usually purple-coloured and up to 0.11-0.17 mm in length (Fig. 11E). Polyp armature composed of ornate sclerites (0.14-0.32 mm in length) as well as little flat rods (0.06-0.12 mm; e.g. Fig. 11D). The surface layer contains tiny club scler- ites (foliate to torched) with short handle (Fig. 11A- C), which are the shortest observed amongst Eunicea ...
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... of a diverse array of ornate forms of capstans and spindles usually purple-coloured and up to 0.11-0.17 mm in length (Fig. 11E). Polyp armature composed of ornate sclerites (0.14-0.32 mm in length) as well as little flat rods (0.06-0.12 mm; e.g. Fig. 11D). The surface layer contains tiny club scler- ites (foliate to torched) with short handle (Fig. 11A- C), which are the shortest observed amongst Eunicea ...
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... the results presented here. Eunicea succinea (Pallas,1766) Description: Colonies up to 1 m in height but usually lower than 60 cm. External coloration ocher (dark or clear). Branching pattern from candelabrum to bushy. Some colonies with enlarged and poorly ramified branches (morphotype plantaginea Bayer, 1961; see species comparisons below) (Fig. 1C). Terminal branches with approximately 0.7 mm in diameter. The sclerites from the middle layer enlarged and transparent spindles up to 2 mm in length, usually thin with 0.09-0.2 mm in ...
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Citations
... The octocorals Carijoa riisei, Leptogorgia euryale, and Ellisella schmitti were observed outside the sampling units; thus, there was a total of 55 species. The morphotypes Eunicea calyculata form coronata and Eunicea calyculata form calyculata are considered separate taxa due to the morphological differences detected in the calyces, branches, and sclerites between them in the same habitat (Sánchez 2009). The species Plexaurella fusifera has been considered synonymous with Plexaurella dichotoma (Alcolado 1985). ...
... Four species accounted for the differences over time between the two investigations: Muricea pinnata, Antillogorgia bipinnata, Pterogorgia anceps, and Eunicea succinea form plantaginea; the first was reported by Hernández-Fernández and Alcolado (2007), although they did not specify the type of habitat, while the second and third were found in a reef lagoon, a habitat that was not taken into account in this study. Therefore, there were only three species that accounted for the difference in SR between both studies because E. succinea was reported in our research, and their morphotypes do not have consistent differences to consider them two separate taxa (Sánchez 2009). Taking into account both studies, 32 species were consigned to CC. reported 17 octocoral species in the Guanahacabibes Peninsula, while our study showed more species in only an area of this one (27 species in total in MG). ...
Octocorals provide multiple ecosystem services in coral reefs. Currently, in tropical western Atlantic reefs, the ecological condition of stony coral communities continues to decline; however, octocoral abundance is increasing at several locations throughout the region. The structure of octocoral communities was evaluated in Cuban reefs and was compared with that in the western Atlantic. We used 1 m2 quadrats to count colony numbers by species between 2001–2005 and 2008–2017 at 189 sampling sites. With 55 species, the octocoral richness in Cuban reefs constitutes one of the highest in this region. Among areas sampled during 2001–2005, the best ecological conditions for octocoral communities were found in Gardens of the Queen and Coco Key; here, octocorals had the greatest richness, diversity, and density. Among areas sampled during 2008–2017, the best ecological conditions for octocoral communities were in Colorados, Sabana-Camagüey, Canarreos, Artemisa, Mayabeque, and Havana (except in four highly polluted sites), where they showed the greatest richness and density. Antillogorgia americana and Eunicea flexuosa had wide distributions in Cuban reefs, except at some sites under the chronic influence of discharges from polluted watersheds in Havana. At those sites, the richness, diversity, and density of octocorals decreased, and their species composition changed toward more tolerant taxa to pollution and sedimentation.
... Prior to that, P. kuna was commonly confused with P. homomalla. Sánchez (2009) presented revisions for candelabrum octocorals of the genus Eunicea and added E. tayrona as a new species in 2009, which closely resembles E. fusca but has distinctly reduced sclerites. Based upon molecular studies, P. flexuosa was reassigned to E. flexuosa by Grajales et al. (2007). ...
... Sexual reproduction is considered the dominant mode for most Caribbean symbiotic species (Kahng et al. 2011). However, new colonies of Plexaura kuna, Eunicea fusca, for example, may also form asexually via vegetative propagation (Lasker 1984;Coffroth and Lasker 1998;Sánchez 2009). Sexual reproductive modes can be divided into three categories: broadcast spawning, internal brooding, and external brooding (Table 3). ...
... Studies of asexual propagation in Caribbean gorgonian species are sparse. The only well-studied species thus far are Plexaura kuna (Lasker 1984;Coffroth and Lasker 1998) and Eunicea fusca (Sánchez 2009). Asexual propagation may allow for higher rates of population increase and therefore, the ability to survive and recover quickly after disturbances such as storms (Lasker 1984). ...
While scleractinian coral populations continue to diminish throughout the Caribbean, gorgonian corals are showing signs of resilience and in some areas are thriving. Despite their prominence on reefs, gorgonian species are notoriously difficult to field identify and as such have been underrepresented in most monitoring efforts. However, with reports of increased resistance to elevated temperatures, ocean acidification, and nutrient enrichment, there is now a growing interest in the ecological and physiological mechanisms that contribute to their success in changing environmental conditions. Here, we compile widely scattered taxonomical, biological, and ecological research on shallow-water symbiotic gorgonians in the wider Caribbean into a comprehensive resource document that can be used by researchers and managers to inform and promote future studies. Each section provides a brief summary of past research, accessible bibliography, and suggestions for future work.
... All specimens were examined under the optical and/or compound microscope for morphological identification and contrasted against species keys (if available) and/or taxonomic descriptions. For scleractinian corals we used Cairns, 2000; for Stylasteridae Cairns et al., 1986; for black corals Opresko and Sánchez, 2005; for octocorals Bayer, 1961;Bayer andGrasshoff, 1994, 1995;Sánchez and Wirshing, 2005;Sánchez, 2009. In addition, several species accounts for Colombia were also useful in species identification (Flórez et al., 2010;Chacón-Gómez et al., 2012;Santodomingo et al., 2013). ...
... Octocorals in the tropical shallow seas are remarkably diverse. Over 10 species from the same genus can be found in sympatry within just a 10 m 2 area in the Caribbean Sea, for example (Sánchez 2009;. However, these highly diverse gorgonian coral communities at both sides of tropical America have unknown origins. ...
... Most plexaurids (Eunicea, Plexaura, and Pseudoplexaura) and sea fans (Gorgonia ventalina) are gonochoric broadcast spawners and some sea feathers (Antillogorgia) and sea ribbons (Pterogorgia) surface brooders (Kahng et al. 2011). Caribbean broadcast spawners octocorals (Eunicea) have among others the largest egg diameters and volumes (Sánchez 2009), which could be related to long larval dispersal. As in Caribbean broadcast-spawning corals (Foster et al. 2012), panmixia among distant populations has also been found in gorgonian corals with this strategy (Andras et al. 2013;Prada and Hellberg 2013). ...
... As in Caribbean broadcast-spawning corals (Foster et al. 2012), panmixia among distant populations has also been found in gorgonian corals with this strategy (Andras et al. 2013;Prada and Hellberg 2013). Surface brooders, which larvae do not travel far (Gutiérrez-Rodríguez and Lasker 2004), have shown a strong genetic structure among hundreds to thousands of kilometers (Gutierrez-Rodriguez et al. 2005, 2009Lasker and Porto-Hannes 2015) and even tenths of meters (Smilansky and Lasker 2014), which suggests that gorgonians with this strategy tend to have a philopatric distribution. ...
Octocoral animal forests (Gorgoniidae and Plexauridae: Octocorallia) at both sides of tropical America provide a unique and characteristic seascape. They can reach over 2 m in height and even form a closed “canopy” in the densest communities. As a functional forest, gorgonian corals provide feeding substrate and habitat for diverse associated biota. This shallow-water fauna was evidently affected by the closure of the Isthmus of Panama, which provided new and different ecological opportunities at both sides. The different ecological settings provided opportunities for these groups to undergo separate adaptive radiations. New ecological conditions could lead to diversification in this group. At the Tropical Eastern Pacific (TEP), new planktonic resources provided new niches for suspension-feeding organisms, such as azooxanthellated gorgonian corals, and could have driven an adaptive radiation to exploit the new food sources. In the Caribbean, there is evidence of ecological speciation in some genera, and the scenario of ecological divergence as a major driver of gorgonian coral diversification is very likely. Thus far, the developmental phenotypic plasticity that we see today in transisthmian gorgonian corals is not just the product of speciation but adaptive developmental plasticity, and it needs further study. Gorgonian corals are today affected by many of the stressors predicted by global change, such as an increase in the frequency and intensity of tropical storms, rising seawater temperatures, and invasive species, yet these cnidarians seem highly resilient to bleaching and ocean acidification conditions. However, there is a link between high thermal anomalies and gorgonian coral immunity, which is associated to disease outbreaks and mass mortalities in sea fans in the Caribbean since the 1980s and more recently in the TEP.
... Octocorals in the tropical shallow seas are remarkably diverse. Over 10 species from the same genus can be found in sympatry within just a 10 m 2 area in the Caribbean Sea, for example (Sánchez 2009;. However, these highly diverse gorgonian coral communities at both sides of tropical America have unknown origins. ...
... Most plexaurids (Eunicea, Plexaura, and Pseudoplexaura) and sea fans (Gorgonia ventalina) are gonochoric broadcast spawners and some sea feathers (Antillogorgia) and sea ribbons (Pterogorgia) surface brooders (Kahng et al. 2011). Caribbean broadcast spawners octocorals (Eunicea) have among others the largest egg diameters and volumes (Sánchez 2009), which could be related to long larval dispersal. As in Caribbean broadcast-spawning corals (Foster et al. 2012), panmixia among distant populations has also been found in gorgonian corals with this strategy (Andras et al. 2013;Prada and Hellberg 2013). ...
... As in Caribbean broadcast-spawning corals (Foster et al. 2012), panmixia among distant populations has also been found in gorgonian corals with this strategy (Andras et al. 2013;Prada and Hellberg 2013). Surface brooders, which larvae do not travel far (Gutiérrez-Rodríguez and Lasker 2004), have shown a strong genetic structure among hundreds to thousands of kilometers (Gutierrez-Rodriguez et al. 2005, 2009Lasker and Porto-Hannes 2015) and even tenths of meters (Smilansky and Lasker 2014), which suggests that gorgonians with this strategy tend to have a philopatric distribution. ...
Octocoral animal forests (Gorgoniidae and Plexauridae: Octocorallia) at both sides of tropical America provide a unique and characteristic seascape. They can reach over 2 m in height and even form a closed “canopy” in the densest communities. As a functional forest, gorgonian corals provide feeding substrate and habitat for diverse associated biota. This shallow-water fauna was evidently affected by the closure of the Isthmus of Panama, which provided new and different ecological opportunities at both sides. The different ecological settings provided opportunities for these groups to undergo separate adaptive radiations. New ecological conditions could lead to diversification in this group. At the Tropical Eastern Pacific (TEP), new planktonic resources provided new niches for suspension-feeding organisms, such as azooxanthellated gorgonian corals, and could have driven an adaptive radiation to exploit the new food sources. In the Caribbean, there is evidence of ecological speciation in some genera, and the scenario of ecological divergence as a major driver of gorgonian coral diversification is very likely. Thus far, the developmental phenotypic plasticity that we see today in transisthmian gorgonian corals is not just the product of speciation but adaptive developmental plasticity, and it needs further study. Gorgonian corals are today affected by many of the stressors predicted by global change, such as an increase in the frequency and intensity of tropical storms, rising seawater temperatures, and invasive species, yet these cnidarians seem highly resilient to bleaching and ocean acidification conditions. However, there is a link between high thermal anomalies and gorgonian coral immunity, which is associated to disease outbreaks and mass mortalities in sea fans in the Caribbean since the 1980s and more recently in the TEP.
... Images of the colony and a close-up image of the collected branch were also obtained. Identifications were based on Bayer (1961) and Sánchez (2009). ...
The incidence of octocoral-octocoral interactions and the physical effects of the interactions were determined in surveys of 29 branching octocoral species at 2 sites in St. John, U.S. Virgin Islands. Close proximity, defined as the bases or branches of octocorals being within 5 cm of each other, creates the potential for direct competitive interactions. Cases of close proximity were common (63 and 34% of the colonies at the 2 sites), and were more abundant at the site with higher colony density and proportionately more colonies with tall, highly branched morphologies. Damaged branches associated with neighboring colonies were found in 19% of the colonies in close proximity. Eunicea flexuosa colonies exhibited less damage than the 5 most common species it interacted with (Antillogorgia americana, Eunicea mammosa, Gorgonia ventalina, Pseudoplexaura crucis, and Pseudoplexaura wagenaari). Of the colonies in close proximity, 23% featured asymmetric colony forms, representing the effects of competition through the preemption of canopy space. G. ventalina had the highest incidence of asymmetry. Nearest-neighbor analyses detected a weak but significant signal of competition in the combined sizes of neighboring colonies. Competition among octocorals in the canopy probably has limited effects on their spatial distribution, but tissue damage and altered colony form could affect growth and fitness.
... To achieve this, four discrete characters and four continuous characters, were evaluated for each species. For the discrete characters, the traits were extracted from the literature [49, 50], which included: colony shape (encrusting, flagelliform, pinnate, candelabrum-like, bushy, fan-like or feather-like), branch shape (cylindrical, flattened or no branching), branching plane (single, multiple or no branching) and the presence/absence of zooxanthellae. For the continuous data, all samples deposited in the Museo de Historia Natural of Universidad de los Andes (ANDES) that were collected at the research sites were used. ...
What are the determinant factors of community assemblies in the most diverse ecosystem in the ocean? Coral reefs can be divided in continental (i.e., reefs that develop on the continental shelf, including siliciclastic reefs) and oceanic (i.e., far off the continental shelf, usually on volcanic substratum); whether or not these habitat differences impose community-wide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown.
Studying Caribbean octocorals as model system, we determined the phylogenetic community structure in a coral reef community, making emphasis on species coexistence evidenced on trait evolution and environmental feedbacks. Forty-nine species represented in five families constituted the species pool from which a phylogenetic tree was reconstructed using mtDNA. We included data from 11 localities in the Western Caribbean (Colombia) including most reef types. To test diversity-environment and phenotype-environment relationships, phylogenetic community structure and trait evolution we carried out comparative analyses implementing ecological and evolutionary approaches.
Phylogenetic inferences suggest clustering of oceanic reefs (e.g., atolls) contrasting with phylogenetic overdispersion of continental reefs (e.g., reefs banks). Additionally, atolls and barrier reefs had the highest species diversity (Shannon index) whereas phylogenetic diversity was higher in reef banks. The discriminant component analysis supported this differentiation between oceanic and continental reefs, where continental octocoral species tend to have greater calyx apertures, thicker branches, prominent calyces and azooxanthellate species. This analysis also indicated a clear separation between the slope and the remaining habitats, caused by the presence or absence of Symbiodinium. K statistic analysis showed that this trait is conserved as well as the branch shape.
There was strong octocoral community structure with opposite diversity and composition patterns between oceanic and continental reefs. Even habitats with similar depths and overall environmental conditions did not share similar communities between oceanic and continental reefs. This indicates a strong regional influence over the local communities, probably due to water transparency differences between major reef types, i.e., oceanic vs. continental shelf-neritic. This was supported by contrasting patterns found in morphology, composition and evolutionary history of the species between atolls and reef banks.
... Phylogenetic differences between the two eunicids may explain the observed patterns in protein content. The genus Eunicea has two sub-genera, with a total of 15 known species (Bayer, 1961;Sánchez, 2009) and is one of the most diverse genera of gorgonians in the Caribbean (Bayer, 1961;Sánchez and Wirshing, 2005). ...
... To determine how E. fusca will respond to ocean acidification, the calcification and growth were measured after exposure to a range of different concentrations of CO 2 over a 4-week period. E. fusca is a member of the most speciose octocoral genus in the Caribbean region and is one of the most abundant shallow-water octocorals in the tropical western Atlantic given its notable vegetative propagation and clonality (Sánchez 2009). ...
... Four types of sclerites were analyzed: spindles, capstans, clubs, and rods (Fig. 1). Spindle sclerites (Fig. 1a) are part of the middle layers, which are normally the biggest sclerites found in the colony; club sclerites, which can be foliate, tuberculate or spinose (Bayer 1961) (Fig. 1b) are part of the outer rind and are unique to this group of octocorals (Sánchez 2009); spindles sclerites sometimes turn into capstans (Fig. 1c) (Bayer 1961) and are normally surrounding the axial sheath close to the axis, some of which elongate to form rods such as the anthocodial crown of the polyps (Fig. 1d) (Sánchez 2009). Sclerites in octocorals have different functions, serving as physical defenses to deter predators (Harvell et al. 1988) and as support for the different structures such as the spindles arranged in parallel along stem canals (Morales-Pinzón et al. 2014). ...
Ocean acidification can have negative reper- cussions from the organism to ecosystem levels. Octocorals deposit high-magnesium calcite in their skeletons, and according to different models, they could be more sus- ceptible to the depletion of carbonate ions than either calcite or aragonite-depositing organisms. This study investigated the response of the gorgonian coral Eunicea fusca to a range of CO2 concentrations from 285 to 4,568 ppm (pH range 8.1–7.1) over a 4-week period. Gorgonian growth and calcification were measured at each level of CO2 as linear extension rate and percent change in buoyant weight and calcein incorporation in individual sclerites, respectively. There was a significant negative relationship for calcification and CO2 concentration that was well explained by a linear model regression analysis for both buoyant weight and calcein staining. In general, growth and calcification did not stop in any of the con- centrations of pCO2; however, some of the octocoral fragments experienced negative calcification at undersaturated levels of calcium carbonate ([4,500 ppm) suggesting possible dissolution effects. These results highlight the susceptibility of the gorgonian coral E. fusca to elevated levels of carbon dioxide but suggest that E. fusca could still survive well in mid-term ocean acidifi- cation conditions expected by the end of this century, which provides important information on the effects of ocean acidification on the dynamics of coral reef commu- nities. Gorgonian corals can be expected to diversify and thrive in the Atlantic–Eastern Pacific; as scleractinian corals decline, it is likely to expect a shift in these reef communities from scleractinian coral dominated to octo- coral/soft coral dominated under a ‘‘business as usual’’ scenario of CO2 emissions.
... Candelabrum corals of the genus Eunicea constitute one such group where sister species are segregated by depth (13). Eunicea constitutes the most diverse genus of anthozoans (anemones, corals, and their kin) on Caribbean reefs, with 15 species plus some undescribed forms (18). Eunicea species share a mutualistic relationship with algae of the genus Symbiodinum clade B (19), which restricts them to the photic zone. ...
... Eunicea species share a mutualistic relationship with algae of the genus Symbiodinum clade B (19), which restricts them to the photic zone. All Eunicea are gonochoric and reproduce sexually by spawning gametes (18,20). ...
... Eunicea flexuosa is an especially suitable species in which to test the effects of immigrant inviability associated with adaptation to depth in a wide geographical context because (i) its geographic range spans the Caribbean (18), (ii) it is common [>5 colonies/m 2 (21)] and present in virtually all habitats and depths on coral reefs and rocky walls (18), (iii) depth-segregated colonies show extensive internal and external morphological differences (13,22), (iv) transplant experiments show colonies are adapted to different depths (13), and (v) first reproduction does not occur until a size of 30 cm, at least 15 y after larval dispersal (20). Such delayed reproduction during sedentary asexual growth allows selection to act for a long time before genes can be mixed [as in the strawberry-coral model of Williams (23)] and thus may increase the intensity of immigrant inviability between depthsegregated populations. ...
Long-lived corals, the foundation of modern reefs, often follow ecological gradients, so that populations or sister species segregate by habitat. Adaptive divergence maintains sympatric congeners after secondary contact or may even generate species by natural selection in the face of gene flow. Such ecological divergence, initially between alternative phenotypes within populations, may be aided by immigrant inviability, especially when a long period separates larval dispersal and the onset of reproduction, during which selection can sort lineages to match different habitats. Here, we evaluate the strength of one ecological factor (depth) to isolate populations by comparing the genes and morphologies of pairs of depth-segregated populations of the candelabrum coral Eunicea flexuosa across the Caribbean. Eunicea is endemic to the Caribbean and all sister species co-occur. Eunicea flexuosa is widespread both geographically and across reef habitats. Our genetic analysis revealed two depth-segregated lineages. Field survivorship data, combined with estimates of selection coefficients based on transplant experiments, suggest that selection is strong enough to segregate these two lineages. Genetic exchange between the Shallow and Deep lineages occurred either immediately after divergence or the two have diverged with gene flow. Migration occurs asymmetrically from the Shallow to Deep lineage. Limited recruitment to reproductive age, even under weak annual selection advantage, is sufficient to generate habitat segregation because of the cumulative prolonged prereproductive selection. Ecological factors associated with depth can act as filters generating strong barriers to gene flow, altering morphologies, and contributing to the potential for speciation in the sea.
