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In the Caribbean, reef-building scleractinian corals have declined precipitously and octocorals have emerged as one of their main successors. The success of octocorals and the formation of octocoral forests has been attributed to their continuing recruitment to reef habitats, as well as tolerance to pollution, reduced direct competition with scleractinians, and resistance and resilience to climatic events. Benthic grazers on coral reefs can facilitate the growth and recruitment of corals by reducing the abundance of competitive algal turfs and macroalgae. However, grazing can also hinder corals through sublethal damage to coral tissue and predation of recruits. We assessed the effects of grazing by fishes and the sea urchin Diadema antillarum as well as predation by mesofauna on octocoral recruitment through a series of manipulative in situ and ex situ experiments. Exposure to fish and urchin grazing significantly reduced the post-settlement survival of octocoral recruits, while turf-associated mesofauna did not significantly affect recruitment. We also found a positive relationship between octocoral recruitment and the abundance of turf algae, which may reflect the deleterious effect of grazing on both turf algae and octocoral recruits. These data suggest that grazers and predators mediate the bottleneck characteristic of recruitment, primarily through their effect on post-settlement survival. Thus, the declines in the abundance of grazing fishes and urchins throughout the Caribbean may have contributed to the increase in Caribbean octocoral abundance, concurrent with the loss of scleractinians. [ABSTRACT FROM AUTHOR]

The reproductive biology of the branching octocoral Antillogorgia americana was studied at a site on the Caribbean coast of Panama in 1990–1991 by examining the reproductive status of 11 colonies across 14 months. Colonies were gonochoric. The presence of large and mature eggs or spermaries was allochronic across colonies and months, with peak gonad volumes occurring in months ranging from October through May. Reproductive effort varied between branches on a colony, with variation between branches and branchlets accounting for 25% of the random variation between polyps. Branchlets at the tip of the colony had fewer mature eggs than those lower on the branch, and polyps at the tips of the branchlets had fewer still. Although the simultaneous release of eggs and sperm is critical to reproductive success, the lack of synchrony among colonies on the scale of months may reflect less need for all colonies to spawn in a single event among abundant species that release large numbers of gametes. Such a strategy also spreads the risk of reproductive failure due to environmental conditions during any single month. The presence of multiple spawning episodes can also drive the reproductive isolation of populations and may reflect the presence of cryptic species within the taxon. Studies of reproductive timing can be an important adjunct in identifying variation in life history strategies as well as assessing the validity of species boundaries. [ABSTRACT FROM AUTHOR]

As the major form of coral reef regime shift, stony coral to macroalgal transitions have received considerable attention. In the Caribbean, however, regime shifts in which scleractinian corals are replaced by octocoral assemblages hold potential for maintaining reef associated communities. Accordingly, forecasting the resilience of octocoral assemblages to future disturbance regimes is necessary to understand these assemblages' capacity to maintain reef biodiversity. We parameterised integral projection models quantifying the survival, growth, and recruitment of the octocorals, Antillogorgia americana, Gorgonia ventalina, and Eunicea flexuosa, in St John, US Virgin Islands, before, during, and after severe hurricane disturbance. Using these models, we forecast the density of populations of each species under varying future hurricane regimes. We demonstrate that although hurricanes reduce population growth, A. americana, G. ventalina, and E. flexuosa each display a capacity for quick recovery following storm disturbance. Despite this recovery potential, we illustrate how the population dynamics of each species correspond with a longer-term decline in their population densities. Despite their resilience to periodic physical disturbance events, ongoing global change jeopardises the future viability of octocoral assemblages. [ABSTRACT FROM AUTHOR]

The three‐dimensional structure of habitats is a critical component of species' niches driving coexistence in species‐rich ecosystems. However, its influence on structuring and partitioning recruitment niches has not been widely addressed. We developed a new method to combine species distribution modelling and structure from motion, and characterized three‐dimensional recruitment niches of two ecosystem engineers on Caribbean coral reefs, scleractinian corals and gorgonians. Fine‐scale roughness was the most important predictor of suitable habitat for both taxa, and their niches largely overlapped, primarily due to scleractinians' broader niche breadth. Crevices and holes at mm scales on calcareous rock with low coral cover were more suitable for octocorals than for scleractinian recruits, suggesting that the decline in scleractinian corals is facilitating the recruitment of octocorals on contemporary Caribbean reefs. However, the relative abundances of the taxa were independent of the amount of suitable habitat on the reef, emphasizing that niche processes alone do not predict recruitment rates. [ABSTRACT FROM AUTHOR]

Background: Among species with size structured demography, population structure is determined by size specific survival and growth rates. This interplay is particularly important among recently settled colonial invertebrates for which survival is low and growth is the only way of escaping the high mortality that small colonies are subject to. Gorgonian corals settling on reefs can grow into colonies of millions of polyps and can be meters tall. However, all colonies start their benthic lives as single polyps, which are subject to high mortality rates. Annual survival among these species increases with size, reflecting the ability of colonies to increasingly survive partial mortality as they grow larger. Methods: Data on survival and growth of gorgonian recruits in the genera Eunicea and Pseudoplexaura at two sites on the southern coast of St John, US Virgin Islands were used to generate a stage structured model that characterizes growth of recruits from 0.3 cm until they reach 5 cm height. The model used the frequency distributions of colony growth rates to incorporate variability into the model. Results: High probabilities of zero and negative growth increase the time necessary to reach 5 cm and extends the demographic bottleneck caused by high mortality to multiple years. Only 5% of the recruits in the model survived and reached 5 cm height and, on average, recruits required 3 y to reach 5 cm height. Field measurements of recruitment rates often use colony height to differentiate recruits from older colonies, but height cannot unambiguously identify recruits due to the highly variable nature of colony growth. Our model shows how recruitment rates based on height average recruitment and survival across more than a single year, but size-based definitions of recruitment if consistently used can characterize the role of supply and early survival in the population dynamics of species. [ABSTRACT FROM AUTHOR]

Octocorals are conspicuous members of coral reefs and deep-sea ecosystems. Yet, species boundaries and taxonomic relationships within this group remain poorly understood, hindering our understanding of this essential component of the marine fauna. We used a multifaceted approach to revisit the systematics of the Caribbean octocorals Plexaura homomalla and Plexaura kükenthali, two taxa that have a long history of taxonomic revisions. We integrated morphological and reproductive analyses with high-throughput sequencing technology to clarify the relationship between these common gorgonians. Although size and shape of the sclerites are significantly different, there is overlap in the distributions making identification based on sclerites alone difficult. Differences in reproductive timing and mode of larval development were detected, suggesting possible mechanisms of pre-zygotic isolation. Furthermore, there are substantial genetic differences and clear separation of the two species in nuclear introns and single-nucleotide polymorphisms obtained from de novo assembled transcriptomes. Despite these differences, analyses with SNPs suggest that hybridization is still possible between the two groups. The two nascent species also differed in their symbiont communities (genus Breviolum) across multiple sampling sites in the Caribbean. Despite a complicated history of taxonomic revisions, our results support the differentiation of P. homomalla and P. kükenthali, emphasizing that integrative approaches are essential for Anthozoan systematics. [ABSTRACT FROM AUTHOR]

Patterns of population biology and community structure can be studied by looking closely at the ontogeny and reproductive biology of reef‐building organisms. This knowledge is particularly important for Caribbean octocorals, which seem to be more resilient to long‐term environmental change than scleractinian corals and provide some of the same ecological services. We monitored the development of the black sea rod, Plexaura homomalla, a common, widely distributed octocoral on shallow Caribbean reefs, from eggs to three‐polyp colonies over the course of 10 weeks. Gametes were collected ex situ on St. John, U.S. Virgin Islands, during spawning events that occurred 3–6 days after the July full moon. Cleavage started 3.0 hr after fertilization and was holoblastic, equal, and radial. Embryos were positively buoyant until becoming planulae at 3 days after fertilization. Planulae were competent to settle 4 days after fertilization. Symbiodiniaceae began infecting polyps ~8 days after fertilization. Overall, development was typical for Caribbean octocorals, except for an increase in the number of embryos between 3.5 and 6.0 hr after fertilization. [ABSTRACT FROM AUTHOR]

More branches on severely clipped colonies (reduced to four branches; 72.4%) underwent positive growth compared to colonies that were clipped to 10 branches (65.3%) or not clipped (62.6%). The differences among colonies in total number of mother branches had only a small effect on the overall number of new branches generated on each mother branch (corrected Figure 4). Moderately clipped colonies from Abaco (clipped to 10 branches) had more new branches per mother branch in comparison to moderately clipped colonies from San Salvador and to severely clipped colonies at both sites (which had similar numbers of new branches per source branch; corrected Figure 3B). [Extracted from the article]

Successful recruitment is critical to the maintenance and resilience of populations and may be at the core of the transition from scleractinian- to octocoral-dominated faunas on some Caribbean reefs. For sessile invertebrates, recruitment incorporates the composite effects of larval supply, settlement and survival. The relative success of these processes differs between species, and successful recruitment may be achieved through different life history strategies. Recruitment of six abundant and widespread Antillogorgia spp. was assessed at six sites on Little Bahama Bank from 2009–2012. Identification of recruits to species level, based on microsatellite analyses, revealed differences in recruitment and survival between species, sites and years. The broadcast spawning species, A. americana and A. acerosa, had low rates of early recruitment and post-settlement survival. Higher levels of recruitment success were achieved among brooding and surface brooding species following somewhat different patterns of early recruitment and survival. The internal brooder A. hystrix had the highest recruitment at five of the sites, but low survival dramatically reduced its abundance and after a year it had similar densities as the surface brooding species, A. elisabethae and A. bipinnata. The brooders have smaller colonies and produce fewer larvae than the broadcast spawning species, but they release competent larvae, which may account for their higher recruitment rates. The Antillogorgia illustrate the diversity of successful reproductive strategies exhibited by octocorals, and differences in the life history strategies among these congeners are best characterized by their mode of larval development. [ABSTRACT FROM AUTHOR]

Coral reefs throughout the tropics have experienced large declines in the abundance of scleractinian corals over the last few decades, and some reefs are becoming functionally dominated by animal taxa other than scleractinians. This phenomenon is striking on many shallow reefs in the tropical western Atlantic, where arborescent octocorals now are numerically and functionally dominant. Octocorals are one of several taxa that have been overlooked for decades in analyses of coral reef community dynamics, and our understanding of why octocorals are favoured (whereas scleractinians are not) on some modern reefs, and how they will affect the function of future reef communities, is not commensurate with the task of scientifically responding to the coral reef crisis. We summarize the biological and ecological features predisposing octocorals for success under contemporary conditions, and focus on those features that could have generated resistance and resilience of octocoral populations to environmental change on modern reefs. There is a rich set of opportunities for rapid advancement in understanding the factors driving the success of octocorals on modern reefs, but we underscore three lines of inquiry: (1) the functional implications of strongly mixotrophic, polytrophic, and plastic nutrition, (2) the capacity to recruit at high densities and maintain rapid initial rates of vertical growth, and (3) the emergent properties associated with dense animal forests at high colony densities. [ABSTRACT FROM AUTHOR]

While the decline in cover of scleractinian corals on Caribbean reefs is well known, little attention has been paid to other taxa that might covary in abundance. This study focused on octocorals around St. John and St. Thomas, US Virgin Islands, in order to: (1) describe variation in octocoral communities, (2) test for similarity in distribution of octocorals and scleractinians, and (3) identify factors associated with the distribution of octocorals that have value in understanding how reefs will change in the future. Photoquadrats recorded in 2011 on north and south shores were used to quantify octocoral and scleractinian abundance with generic resolution. MDS and PERMANOVA revealed clearer community variation relative to the spatial scales of investigation for octocorals compared to scleractinians. Multivariate spatial structuring for octocorals differed from that of scleractinians, suggesting the taxa responded in dissimilar ways to the environmental conditions. PCO supported the differences in the structuring of community types and revealed the roles of octocorals ( Eunicea, Briareum, Plexaurella, Muriceopsis, Pterogorgia, and Muricea) in distinguishing among islands, shores, and sites; scleractinians ( Porites, Colpophyllia, Siderastrea, and Orbicella) distinguished sites. These results suggest that changes in the community structure of Caribbean reefs favoring octocorals may promote local-scale provincialization. [ABSTRACT FROM AUTHOR]

The decline in abundance of scleractinian corals over the past three decades in the Caribbean has raised the possibility that other important benthic taxa, such as octocorals, are also changing in abundance. We used photoquadrats taken over 20 yr from reefs (7-9 m depth) at six sites on the south coast of St. John, US Virgin Islands, to test the hypothesis that octocorals have changed in abundance since 1992. Octocorals were counted in 0.25 m photoquadrats at 2- to 3-yr intervals and identified to genus or family. Overall, there was variation over time in population density of octocorals (pooled among taxa, and also separately for Antillogorgia spp., Gorgonia spp., and plexaurids) at each site, and densities remained unchanged or increased over 20 yr; where increases in density occurred, the effects were accentuated after 2002. The local-scale analysis was expanded to the Caribbean (including the Florida Keys) by compiling data for octocoral densities from 31 studies for reefs at ≤25 m depth between 1968 and 2013. At this scale, analyses were limited by the paucity of historical data, and despite a weak trend of higher octocoral densities in recent decades, statistically, there was no change in octocoral abundance over time. Together with data from the whole Caribbean, the present analysis suggests that octocorals have not experienced a decadal-scale decline in population density, which has occurred for many scleractinian corals. [ABSTRACT FROM AUTHOR]

The reproductive biology of the Caribbean gorgonian Antillogorgia hystrix was studied in the shallow-water reefs of Cross Harbour, Great Abaco (The Bahamas) from 2009 to 2010. Antillogorgia hystrix is an internal brooder that reproduces annually. The population at Cross Harbour was gonochoric and the sex ratio was skewed toward females (~3:1). Oogenesis precedes spermatogenesis by several months, and lasts at least 9 months, with oocytes >100 μm in diameter first becoming visible in dissections of samples from February; mature oocytes are present in late October-November. The size of mature oocytes (400-900 μm in diameter) was greater than that of the spermaries, which were rarely larger than 400 μm. Brooded planulae were observed in polyps from early November to mid-December, and planula release was observed in aquaria in December 2009, which suggests that planulation occurs continuously over this period. Planulae of A. hystrix contained dinoflagellate symbionts, presumably acquired during embryogenesis and/or by mature planulae while they were in the gastrovascular cavity of the polyp. Brooding is an uncommon reproductive strategy among Caribbean gorgonians and this is the first report of internal brooding in the genus Antillogorgia. The genus contains a number of sympatric species with different modes of reproduction, and knowledge of their reproductive biology is critical to understand their ecology and evolution. [ABSTRACT FROM AUTHOR]

Larval dispersal is a critical component of marine species' life histories because it controls their population dynamics. Dispersal distance can be inferred by the presence and scale of spatial genetic structure (SGS). The larvae of Antillogorgia elisabethae, a surface brooding Caribbean octocoral, have been observed to settle within meters of maternal colonies, although many disperse over greater distances. Using a spatially hierarchical sampling design, A. elisabethae recruits were collected from a site off the coast of Great Abaco, The Bahamas, in June of 2009-2011. Seven microsatellite loci were used to determine whether genetic structure was present among recruits on scales of <1 m to 10s of meters. Multilocus genotypes were autocorrelated within spatial distance classes using Moran's I coefficient as an estimate of genetic similarity, and Rousset's genetic distance ( â). Genetic structure was present on a scale of <10 m in 2010, but not in the other 2 years, suggesting that larval dispersal was more localized in 2010. Moran's I coefficients were positive and significant for 0-1, 1-2 and 2-5 m classes in 2010, and the average genetic distance ( â) among recruits in the 0-1 m class was significantly lower than the other classes. Autocorrelograms suggested that genetic patch sizes were 7.5 m in 2010, and 20 m in 2009 and 2011. Differences in the SGS of recruits between years might reflect temporal variation in temperature, wind and/or current speeds affecting larval dispersal, or variation in reproduction at the site. [ABSTRACT FROM AUTHOR]

Disturbance events are an important component of the ecology of coral reefs and increasingly frequent disturbances coupled with a lack of population resilience may contribute to changes in the structure of coral reef communities. The harvest of the Caribbean octocoral Antillogorgia elisabethae provides an opportunity to explore the relationship between adult abundance and recruitment and the manner in which recruitment contributes to the resilience of local populations. Recruitment of A. elisabethae was monitored in 20, 1-m2 quadrats at 8 sites along the southern edge of the Little Bahama Bank from 2004 through 2007. A. elisabethae has been harvested in The Bahamas for over fifteen years and all of the sites had been harvested three times, including a harvest during the course of the study. Abundances of adult colonies at those sites as well as a location that had not been harvested were also determined. Recruitment was highly variable, differing between sites, transects within sites, and, depending on the site, between years. Recruitment was best correlated with adult abundance averaged across the surrounding site. Regression analyses suggest abundance on smaller scales had only small effects on recruitment. The effects of the harvesting were site specific ranging from a 38 to 67% reduction in the density of mature colonies. The sites with the most abundant A. elisabethae continued to have the highest abundances after harvesting and there was no significant difference in recruitment before and after harvesting. Population size-structure at 6 of 8 sites that have been harvested multiple times exhibited an overall depletion in small colonies suggesting long term suppression of recruitment and declining populations. Severe depression of adult abundances coupled with local recruitment can create a negative feedback and lead to the decline of local populations. Populations that are dependent on self-recruitment are not resilient to large disturbance events. [ABSTRACT FROM AUTHOR]

In benthic communities sponges commonly outcompete other organisms in the race for suitable space. Superior competitive ability allows them to grow and overgrow other sessile organisms, some of these being octocorals. Acquiring substratum space, a resource often more limiting than food, is the obvious benefit of these competitive interactions. However, sponges that overgrow larger structures such as branching octocorals also change their position in the water column, and potentially their access to food and exposure to grazers. This study explored the potential benefit of sponge-octocoral associations by examining the effect of height off the bottom on growth of two species of ropelike demosponges under natural conditions. The growths of Amphimedon compressa and Iotrochota birotulata were monitored over 12 months at Cross Harbour, Great Abaco, The Bahamas, using small (5-cm) sponge fragments that were established at three heights above the bottom (0-5, 30, 60 cm). Growth rates differed among the two species and among different heights. Over 12 months, the mean volumetric growth for A. compressa was 17.7 cm3 ± 1.4 compared with 8.9 cm3 ± 1.4 for I. birotulata. Both species had a higher growth rate at the 60-cm level. These results suggest that these ropelike sponges benefit from their association and growth on octocorals, not only by using the octocoral skeletal axis as support, but also by acquiring exposure to higher water flow. [ABSTRACT FROM AUTHOR]

Abstract: Clonal organisms have complex life histories in which traits such as reproductive maturity and fecundity are affected by colony size. Thus changes in reproduction due to tissue loss have the potential to affect population dynamics even among seemingly healthy populations. At sites in The Bahamas the octocoral Pseudopterogorgia elisabethae, which produces a natural product used by the skin care industry, is harvested by cropping branches from large sexually mature colonies. Cropping decouples colony size and age and provides the opportunity to assess the effects of colony size, age and tissue loss on reproductive output. Tissue samples from P. elisabethae colonies from Cross Harbour, Abaco, The Bahamas were collected prior to spawning in 2009 and fecundity was determined. Approximately half of the colonies had been harvested 4years earlier. There was no relationship between either age or colony size and reproduction among colonies that were large enough to reproduce. Polyps from female colonies that had previously been cropped produced fewer eggs than those that had not been cropped. In an additional experiment, a group of predominantly male colonies was clipped to a height below the size of first reproduction The clipped colonies were less likely to have reproductive polyps, and the male colonies that were clipped to 10–15cm height had fewer reproductive polyps and fewer spermaries per reproductive polyp than unclipped controls that were 30cm in height. Size affected whether a colony is reproductive, but age had no discernible effect in the observations and experiments. Tissue loss reduced per polyp fecundity. The results coupled with previous findings of enhanced branch extension in cropped colonies suggest that a long term reallocation of energy from reproduction to growth occurs among colonies that have lost branches. [Copyright &y& Elsevier]

The article discusses a study on the systematic and biogeographic patterns of reproduction biology within Octocorallia from 182 species across 25 families and 79 genera. It refers to octocorals as exclusive modular colonial marine invertebrates that reproduce sexually and asexually. Morphological characters were traditionally used to distinguish between taxa among octorals which include colony growth form, axial structure and the size, shape and micro-architecture of sclerites. It indicates differences between the 2 taxa where octocorals are predominantly gonochoric while scleractinians are predominantly hermaphrodites.

Species descriptions of most alcyonacean octocorals rely heavily on the morphology of sclerites, the calcium carbonate spicules embedded in the soft tissue. Sclerites provide taxonomic characters for species delineation but require qualitative descriptions, which introduce ambiguities in recognizing morphological features. Elliptical Fourier analysis of the outline of sclerites was used to quantity the morphology of eight species of gorgoniid octocoral in the genus Pseudopterogorgia. Sclerites from one to seven colonies of each species were compared. Scaphoids and spindles were examined separately; rods and octoradiates were excluded from the analyses because of their morphologic similarity across all species. Discriminant analysis of elliptical Fourier descriptors (EFDs) was used to determine whether the elliptical Fourier analysis could be used to identify the specimens. Sclerites were highly variable even within a single colony. Correct species assignments of individual sclerites were greater than 50% for both scaphoids and spindles. Species assignments based on averages of the EFDs for each colony approached 90%. Elliptical Fourier analysis quantifies morphological differences between species and measures colony variance in sclerite size and shape among colonies and species. Phylogenetic analysis based on EFDs did not capture monophyletic groups. The quantification of complex shapes such as sclerites provides an important tool in alpha taxonomy but may be less useful in phylogenetic analyses. [ABSTRACT FROM AUTHOR]

Growth rates of branches of colonies of the gorgonian Pseudopterogorgia elisabethae were monitored for 2 years on a reef at San Salvador Island, Bahamas. Images of 261 colonies were made at 6-month intervals and colony and branch growth analyzed. Branch growth rates differed between colonies and between the time intervals in which the measurements were made. Colonies developed a plumelike morphology through a pattern of branch origination and determinate growth in which branch growth rates were greatest at the time the branch originated and branches seldom grew beyond a length of 8 cm. A small number of branches had greater growth rates, did not stop growing, and were sites for the origination of subsequent "generations" of branches. The rate of branch origination decreased with each generation of branching, and branch growth rates were lower on larger colonies, leading to determinate colony growth. Although colonial invertebrates like P. elisabethae grow through the addition of polyps, branches behave as modules with determinate growth. Colony form and size is generated by the iterative addition of branches. [ABSTRACT FROM AUTHOR]

Colonies of the branching Caribbean gorgonian Pseudopterogorgia elisabethae were subjected to partial mortality at 2 sites in the Bahamas to study how colony growth responds to disturbances such as harvesting, grazing, and storm damage. Colonies were clipped so that either 4 branches or 10 branches remained. Growth rates of branches were then monitored over 1 year and compared with nearby unclipped colonies. No significant differences were found between branch extension rates among the 3 treatments. Extension rates of newly formed branches were significantly greater in all treatments than among branches present at the start of the experiment. Per capita branching rates were greater on the more severely clipped colonies and were smallest on control colonies. The absolute number of branches that became mother branches did not differ among treatments. Colonies clipped so that 4 and 10 branches remained had the same average number of mother branches per colony, and, there was no significant difference between treatments in the average number of new branches formed on the colonies. Per capita branching rates were significantly different among treatments only because the relative proportion of branches that became mother branches was higher in colonies with four branches than in treatments with more initial branches. Total growth (cumulative growth on all branches) was not significantly different between the 2 clipped treatments. Many of the control colonies suffered extensive damage, which may have obscured the comparison of clipped and unclipped treatments; however, within the range of these clipping treatments, differing levels of partial mortality did not lead to different recovery rates. The lack of treatment effects is particularly relevant to assessing the effects of harvest techniques on the recovery and productivity of harvested, naturally occurring, colonies. [ABSTRACT FROM AUTHOR]

We report on the isolation and characterization of five polymorphic microsatellites in the gorgonian Pseudopterogorgia elisabethae from genomic DNA-enriched libraries. Forty-four microsatellites were screened from the libraries with the oligonucleotide probe (CA)12. Five of the screened microsatellites were polymorphic. The levels of polymorphism found in 50 genotyped individuals from a single population suggest that microsatellites are useful tools for the study of genetic variation in gorgonians. These are the first microsatellite loci reported from any gorgonian species. [ABSTRACT FROM AUTHOR]

Octocorals have increased in abundance on a number of Caribbean reefs, but this trend has largely been reported with functional group or genus resolution. A species-level analysis of octocoral communities in St. John, US Virgin Islands was conducted to better understand how this taxon will respond to changing conditions based on their synecology at two sites that are 1.5 km apart and differ in physical conditions. East Cabritte is characterized by moderate wave energy, low sedimentation, and clear water, while contrasting conditions characterize Europa Bay. Surveys conducted in 2014 and 2015 showed that the abundance and size of adult octocorals differed between sites, with taller and denser communities at East Cabritte than Europa Bay (mean height of 32 versus 20 cm; 18 versus 8 colonies m−2). Octocoral diversity and evenness were similar between sites, although multivariate octocoral community structure differed between sites regardless of whether octocorals were resolved to genera or species. Genus-resolution masked differences between sites for speciose genera like Eunicea. The broad overlap in species representation at both sites suggests that diversity is less responsive than community structure to differing environmental conditions, perhaps because the ecological niches of these species are broad. With 35 octocoral species, and diversity and abundances comparable to those studied > 40 years ago on shallow Caribbean reefs, the dense octocoral communities appearing on some present-day reefs reflect expanded benthic occupancy by a well-known (rather than a novel) community type. [ABSTRACT FROM AUTHOR]

Unlike reef-building, scleractinian corals, Caribbean soft corals (octocorals) have not suffered marked declines in abundance associated with anthropogenic ocean warming. Both octocorals and reef-building scleractinians depend on a nutritional symbiosis with single-celled algae living within their tissues. In both groups, increased ocean temperatures can induce symbiont loss (bleaching) and coral death. Multiple heat waves from 2014 to 2016 resulted in widespread damage to reef ecosystems and provided an opportunity to examine the bleaching response of three Caribbean octocoral species. Symbiont densities declined during the heat waves but recovered quickly, and colony mortality was low. The dominant symbiont genotypes within a host generally did not change, and all colonies hosted symbiont species in the genus Breviolum. Their association with thermally tolerant symbionts likely contributes to the octocoral holobiont's resistance to mortality and the resilience of their symbiont populations. The resistance and resilience of Caribbean octocorals offer clues for the future of coral reefs. [ABSTRACT FROM AUTHOR]