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Branching dynamics of transplanted colonies of the threatened coral Acropora cervicornis: Morphogenesis, complexity, and modeling
Abstract
Acropora cervicornis is a threatened Caribbean coral that depends on branch fragmentation to proliferate. Understanding
the patterns of branch formation is, therefore, essential for the development of management and conservation
initiatives. This study describes branch morphogenesis in 100 colony fragments that were transplanted
to two reefs in Puerto Rico that differ in light intensity. Four morphometric variables were measured for one year:
internode length, branch growth rate, the number of ramifying branches (mother branches; MB), and the number
of branches produced (daughter branches; DB). Branching complexity was also evaluated using two indices:
the Horton-Strahler bifurcation ratio (Rb) and the Carrillo-Mendoza branching index (CM-BI). A simple discrete
model was constructed to estimate the number of harvestable branches over time. No spatial difference was observed
when comparing the development of the primary branches, as the mean internode lengths, the mean extension
rates, and the mean number of branches produced did not differ statistically between sites. Likewise,
internode lengths in secondary branches did not vary significantly between sites. In contrast, the mean branching
and growth rates of secondary branches differed statistically between the two study locations. Significant spatial
differences were also observed when comparing the total number of MB and the total number of DB but not for
the ratio of DB to MB. The CM-BI was more appropriate than the Rb in describing the branching structure of A.
cervicornis. The model provided a good fit to the observed branching dynamics; demonstrating its usefulness
as a tool for predicting branch productivity of this species. The implications for restoration activities are discussed.
... Research by Huston (1985) showed growth rates among corals generally decreased with depth due to light attenuation. Conversely, A. cervicornis outplanted to two sites with similar depths of 3-4 m grew faster at the site that experienced greater light attenuation (Mercado-Molina et al. 2016). Corals have exhibited photoinhibition in shallow, high-light areas (Winters et al. 2003), which may contribute to slower growth. ...
... Corals have exhibited photoinhibition in shallow, high-light areas (Winters et al. 2003), which may contribute to slower growth. It is likely that the faster growing, lower light site from Mercado-Molina et al. (2016) received more photosynthetically available radiation (PAR) than block-grown corals in the present study located at a depth of 8 m. Therefore, PAR availability, which decreases with depth (Jokiel and Lesser, 1997), cannot be ruled out as a potential factor in growth rate difference between culture methods. ...
... Additionally, availability of space in all three dimensions has been shown to allow suspended A. cervicornis colonies to make greater use of their branching growth characteristic. This likely enhances overall production (Lirman et al. 2014) as branching dynamics are a very important factor for growth in this species (Mercado-Molina et al. 2016). Colonies on blocks can grow vertically and horizontally, but are limited in their ability to expand below the plane on which they are fixed. ...
Staghorn coral Acropora cervicornis is an important framework-building species that has declined severely throughout the Caribbean since the early 1980s. This species is now widely cultured in ocean-based nurseries to restore degraded populations. A variety of techniques have been adopted to grow A. cervicornis for restoration purposes, however the effect of each of these methods on nursery-reared corals is not well-understood. In particular, systematic evaluation of nursery-reared A. cervicornis between water column-suspended and benthic-attached culture methods is lacking. To better understand the effect of these techniques, a one-year A. cervicornis propagation experiment in the Florida Keys was conducted to compare growth, condition, and survivorship between common suspended (i.e. tree) and benthic-attached (i.e. block) grow-out methods. The effect of coral genotype on growth was also considered. Colonies were measured and monitored monthly from December 2014 until November 2015, when only three colonies had survived an extreme bleaching event. Colonies on trees grew up to three times faster than those on blocks and the location of colonies on trees did not affect growth. Genotype had a significant effect on colony growth, which was consistent across grow-out methods. Interestingly, colonies grown on blocks bleached sooner but survived longer than those on trees. These findings contribute to a growing understanding of A. cervicornis nursery culture, and could aid in the selection of culture methods and genotypes for coral nurseries throughout the wider Caribbean.
... Historically, A. cervicornis was one of the most dominant and essential reef-builder coral species in the Caribbean [15]. Its broad vertical distribution, i.e., from a 1 to 30 m depth [16], high branching rates, and impressive asexual proliferation due to branch fragmentation [17] allowed this species to dominate vast areas of the reefscape. These so-called "thickets" also provided the necessary structural complexity to sustain a high diversity of fishes, invertebrates, algae, and microbial organisms [18][19][20]. ...
... Even though these conservation measures have provided some level of protection, these alone have had little success at preventing further declines [23]. Consequently, implementing interdisciplinary strategies, such as coral farming, that directly impact A. cervicornis populations across its entire range are imperative [17,24]. ...
Populations of Acropora cervicornis, one of the most important reef-building corals in the Caribbean, have been declining due to human activities and global climate change. This has prompted the development of strategies such as coral farms, aimed at improving the long-term viability of this coral across its geographical range. This study focuses on comprehending how seawater temperature (ST), and light levels (LL) affect the survival and growth of A. cervicornis fragments collected from three reefs in Culebra, Puerto Rico. These individuals were fragmented into three pieces of the similar sizes and placed in farms at 5, 8, and 12 m depth. The fragments, ST and LL were monitored for 11 months. Results show that fragments from shallow farms exhibit significantly higher mortalities when compared to the other two depths. Yet, growth at shallow farms was nearly 24% higher than at the other two depths. Corals grew fastest during winter, when temperature and LL were lowest, regardless of the water depth. Fragment mortality and growth origin were also influenced by reef origin. We conclude that under the current conditions, shallow farms may offer a slight advantage over deep ones provided the higher growth rate at shallow farms and the high fragment survival at all depths.
... APR is a rehabilitation tool that is designed by multilevel substrates and applied the combination both of coral transplantation and artificial reefs. Acropora spp. is generally considered as a good for candidates for use in coral transplantation or population enhancement project due to their high growth rate and high survivorship of fragments (Lirman et al. 2010;Boch and Morse 2012;Mercado-Molina 2016;Schopmeyer et al. 2017). The application of APR with Acropora transplanted on their substrates is considered contributing to the local conservation of the small island reefs in the near future. ...
... The final measurement of volume (length, wide, and height) of the coral fragments were evaluated in late July 2019. The size of the fragments was measured by taking a picture using an underwater camera and putting the scale beside each the fragment (Mercado-Molina et al. 2016). The size measurement of the fragments was analyzed using image analyses of computer software, Image J. Volume of the fragment was determined by ecological volume (EV; de la Cruz et al. 2015), and its calculated following the cylindrical volume formula (Levy et al. 2010) as define, in equation (1) , where ...
Munasik, Sabdono A, Assyfa AN, Wijayanti DP, Sugiyanto, Irwani, Pribadi R. 2020. Coral transplantation on a multilevel substrate of Artificial Patch Reefs: effect of fixing methods on the growth rate of two Acropora species. Biodiversitas 21: 1816-1822. Branching Acropora is generally used in coral transplantation to rehabilitate coral reefs. However, these corals are sensitive to environmental changes. Artificial Patch Reef (APR) is an artificial structure that provides a multilevel hard substrate. The purpose of the study was to investigate the effectiveness of the APR structure to facilitate the growth and survival of Acropora branching. Two species Acropora aspera and Acropora copiosa were transplanted vertically and horizontally on a modular concrete block in different levels of APR situated in the shallow reef of Panjang Island, Central Java. The results showed that the coral growth rate varied from 96.7 to 346.9 cm3/month, while survival ranged from 30 to 100% after 8 months. Lower survival rate mostly was found in the upper level of APR. The statistical analyses showed that the growth rate of A. copiosa fragment was significantly higher than that of A. aspera (p<0.05). Moreover, there were also significant differences in the treatments of transplantation method (p<0.05) to enhance coral growth. However, multilevel substrates were not significantly influenced by coral growth. This study suggested that A. copiosa which has high-level complexity in branching pattern will be selected to apply in shallow reef rehabilitation with transplanted vertically.
... U41 displayed greater variability in metabolite concentration among replicates compared to genotypes U25 and U44, but this variability did not appear to relate to donor colony (A versus B; Fig. 3). PCA components 1 and 2 described 43.6% (positive ion mode) and 44.6% (negative ion mode) of the total variance among genotypes. In PCA models derived from both the positive and negative ion mode, U44 clustered separately from both U25 and U41, however U41 had greater within-group variability compared to the other two genotypes, resulting in overlap with U25 (Fig. 4). ...
... This concept is also supported by a previous study of the soft coral Sinularia, which documented distinct sesquiterpene signatures among species with different morphological and anatomical traits, indicating a possible link between phenotype and metabolome in corals 43 . At present, identification of coral genotypes that possess traits of interest can involve painstaking repeated measurements in situ 25,44 or long-term manipulative experiments 10,45 , which are time-consuming and costly. Recent attempts to identify transcriptomic biomarkers for thermotolerance and other traits of interest in A. cervicornis were complicated www.nature.com/scientificreports ...
Global threats to reefs require urgent efforts to resolve coral attributes that affect survival in a changing environment. Genetically different individuals of the same coral species are known to exhibit different responses to the same environmental conditions. New information on coral physiology, particularly as it relates to genotype, could aid in unraveling mechanisms that facilitate coral survival in the face of stressors. Metabolomic profiling detects a large subset of metabolites in an organism, and, when linked to metabolic pathways, can provide a snapshot of an organism’s physiological state. Identifying metabolites associated with desirable, genotype-specific traits could improve coral selection for restoration and other interventions. A key step toward this goal is determining whether intraspecific variation in coral metabolite profiles can be detected for species of interest, however little information exists to illustrate such differences. To address this gap, we applied untargeted 1H-NMR and LC-MS metabolomic profiling to three genotypes of the threatened coral Acropora cervicornis. Both methods revealed distinct metabolite “fingerprints” for each genotype examined. A number of metabolites driving separation among genotypes were identified or putatively annotated. Pathway analysis suggested differences in protein synthesis among genotypes. For the first time, these data illustrate intraspecific variation in metabolomic profiles for corals in a common garden. Our results contribute to the growing body of work on coral metabolomics and suggest future work could identify specific links between phenotype and metabolite profile in corals.
... Such branched structures include Drosophila trachea [1,2], plant leaf veins [3], and mammalian lungs [4,5], kidneys [6,7], pancreas [8,9], salivary glands [10,11], mammary glands [12,13], and blood vessels [14]. Marine colonial organisms, such as corals, bryozoans, and hydroids, are also branched structures [15][16][17][18]. Although these structures appear to be morphologically diversified, recent molecular and cellular studies of branching morphogenesis, mainly in Drosophila and mammals, have highlighted the common and fundamental principles of organ branch formation. ...
... Scale bars: 200 μm. j A table showing the number of branches with either function that were formed by Day 11, and on the day on which functional nematocysts were acquired for the first time that in other branching systems, including those found in corals and colonial hydroids [16][17][18], in that it occurs at the proximal end of the branching structure. The proximal region of medusa tentacles has been shown to be the site of active cell proliferation in Aurelia and Clytia jellyfish species [30,31], which suggests that cell proliferation may be involved in the proximal branching in C. pacificum. ...
Background
Branched structures are found in many natural settings, and the molecular and cellular mechanisms underlying their formation in animal development have extensively studied in recent years. Despite their importance and the accumulated knowledge from studies on several organs of Drosophila and mammals, much remains unknown about branching mechanisms in other animal species. We chose to study the jellyfish species Cladonema pacificum. Unlike many other jellyfish, this species has branched medusa tentacles, and its basal phylogenetic position in animal evolution makes it an ideal organism for studying and understanding branching morphogenesis more broadly. Branched tentacles are unique compared to other well-studied branched structures in that they have two functionally distinct identities: one with adhesive organs for attaching to a substratum, and another with nematocyst clusters for capturing prey.
Results
We began our analyses on C. pacificum tentacles by observing their branching during growth. We found that tentacle branches form through repeated addition of new branches to the proximal region of the main tentacle while it is elongating. At the site of branch bud formation, we observed apical thickening of the epidermal epithelial layer, possibly caused by extension of the epithelial cells along the apico-basal axis. Interestingly, tentacle branch formation required receptor tyrosine kinase signaling, which is an essential factor for branching morphogenesis in Drosophila and mammals. We also found that new branches form adhesive organs first, and then are transformed into branches with nematocyst clusters as they develop.
Conclusions
These results highlight unique features in branch generation in C. pacificum medusa tentacles and illuminate conserved and fundamental mechanisms by which branched structures are created across a variety of animal species.
... Feeding on large and more complex colonies could also result from the fireworm preferring colonies in a compromised energetic state. For instance, as A. cervicornis grows, it devotes more energy to growth than maintenance and defense (Darling et al., 2012;Mercado-Molina et al., 2016), possibly limiting its ability to counteract fireworm aggression. ...
Introduction:
The fireworm Hermodice carunculata is a widespread polychaete that can prey upon many coral species. However, few studies have examined the effect of fireworm predation on coral demographics during non-outbreak periods.
Objective:
To determine whether predation by H. carunculata compromised the growth, survival, and population performance of the threatened coral Acropora cervicornis.
Methods:
Nursery-reared coral fragments (n = 99) were fixed to the bottom of Punta Melones reef in the Island Municipality of Culebra, Puerto Rico. Predation activity and its demographic consequences on coral outplants were assessed from December 2020 to August 2022. Susceptibility to predation was compared between colonies collected directly from the reef and those originating from outside sources (e.g., coral nurseries). With the demographic data, simple size-based population matrix models were developed to 1) examine whether fireworm predation led to a significant decline in population growth rate (λ), 2) determine the demographic transition(s) that contribute the most to λ, and 3) determining the demographic transition(s) that accounted for differences in λ when comparing scenarios that considered either only predated colonies or both predated and non-predated outplants.
Results:
Predation increased over time, being more frequently observed in the area with the highest topographic relief and on colonies foreign to the study site. Outplants that were partially consumed grew significantly slower than non-predated colonies; however, predation did not threaten their survival. The likelihood of being attacked by the fireworm increased with branching complexity. The estimated λ for a scenario considering only predated colonies was 0.99, whereas, for a scenario where both predated and non-predated colonies were considered, λ was 0.91. Population growth, under the two scenarios, was mainly influenced by the probability of a large colony surviving and remaining at the largest size.
Conclusions:
Although predation can negatively impact coral growth, the relatively high survival rate of predated colonies compensates for the adverse effect. Since survival is the demographic transition that contributes most to population growth, it could be concluded that under a non-outbreak scenario, fireworm predation may not be the primary cause of A. cervicornis population decline.
... However, this model assumes dispersal and movement of fecund individuals between spatial cells that are not present in coral populations. Current population viability analyses in corals have been limited to asexual restoration (Mercado-Molina et al. 2016) or exclusively wild larval recruitment scenarios (Muko et al. 2014). Coral restoration interventions require a model that can account for both asexual restoration efforts combined with densitydependent success of sexual restoration efforts in these sessile species. ...
As natural coral populations decline, thousands of outplanted corals are poised to dominate reefs in the hardest-hit areas, such as the Florida Keys. Genetic management plans are urgently needed to prevent unintended erosion of genetic diversity in managed populations. Drivers of genetic diversity loss include limited nursery genets available for outplanting or that these genets were reared from crosses among a limited number of parent genets. Existing data indicate that captive rearing of coral larvae can impose substantial genetic bottlenecks that result in closely related cohorts. Thus, questions arise about how to safeguard genetic diversity and optimize the adaptation potential of restored populations. What is the optimal ratio of asexually propagated colonies to sexually produced coral recruits at each site? What breeding scheme should be used if a limited number of donor genets are available? Should breeding be selective to achieve a shift in phenotypes such as thermotolerance at the risk of losing genetic diversity? Population viability analyses (PVA) can answer some of these questions, but current models need to be modified to resolve the most pressing issues. This chapter discusses omics methods to determine genetic diversity of corals and their symbionts and outlines strategies to achieve genetic diversity goals.KeywordsGenetic diversityCoral restorationCoral breedingInbreedingEvolutionary potentialPopulation viability model
... Intraspecific variation in the traits of foundation species, such as reef-building corals, seagrasses, and mangroves, can have widespread effects on the regulating contributions of ecosystems. For example, phenotypic diversity in growth and branching patterns of the reef-forming staghorn coral (Acropora cervicornis) ensures long-term stability of the communities they support 74,75 . Trade-offs between branch density and growth rate in staghorn coral influence resistance to breakage, an important determinant of the reef 's ability to buffer storm surges 76 . ...
The rapid loss of intraspecific variation is a hidden biodiversity crisis. Intraspecific variation, which includes the genomic and phenotypic diversity found within and among populations, is threatened by local extinctions, abundance declines, and anthropogenic selection. However, biodiversity assessments often fail to highlight this loss of diversity within species. We review the literature on how intraspecific variation supports critical ecological functions and nature’s contributions to people (NCP). Results show that the main categories of NCP (material, non-material, and regulating) are supported by intraspecific variation. We highlight new strategies that are needed to further explore these connections and to make explicit the value of intraspecific variation for NCP. These strategies will require collaboration with local and Indigenous groups who possess critical knowledge on the relationships between intraspecific variation and ecosystem function. New genomic methods provide a promising set of tools to uncover hidden variation. Urgent action is needed to document, conserve, and restore the intraspecific variation that supports nature and people. Thus, we propose that the maintenance and restoration of intraspecific variation should be raised to a major global conservation objective. This Perspective highlights how conservation of intraspecific variation is critical for sustaining nature’s contributions to people.
... The most evident non-lethal effect of diseases is the reduction in colony size due to tissue loss Mercado-Molina et al., 2018;Pisapia et al., 2020;Riegl et al., 2017Riegl et al., , 2018. Compared to large colonies, small-sized colonies show: 1) lower survival rates, 2) lower sexual reproductive performance (Soong and Lang, 1992), and 3) produce a lower number of branches, which is vital for the propagation of the Caribbean acroporids species (Mercado-Molina et al., 2016;Vardi et al., 2012). Moreover, the demographic performance of A. cervicornis is also associated with the amount of lost tissue (Mercado-Molina et al., 2018). ...
Chronic coral reef degradation has been characterized by a significant decline in the population abundance and live tissue cover of scleractinian corals across the wider Caribbean. Acropora cervicornis is among the species whose populations have suffered an unprecedented collapse throughout the region. This species, which once dominated the shallow-water reef communities, is susceptible to a wide range of stressors, resulting in a general lack of recovery following disturbances. A. cervicornis is a critical contributor to the structure, function, and resilience of Caribbean coral reefs. Therefore, it is essential to identify the factors that influence their demographic and population performance. Diseases are one of the factors that are compromising the recovery of coral populations. In this chapter, we use size-based population matrix models to evaluate the population-level effect of a Shut Down Reaction Disease (SDR) outbreak, one of the less-understood diseases affecting this coral. The model was parameterized by following the fate of 105 colonies for 2 years at Tamarindo reef in Culebra, Puerto Rico. SDR, which affected 78% of the population, led to a rapid decline in colony abundance. The estimated population growth rate (λ) for the diseased population was more than six times lower than would be expected for a population at equilibrium. It was found that colonies in the smaller size class (≤ 100 cm total linear length) were more likely to get infected and succumbing to the disease than larger colonies. Model simulations indicate that: (1) under the estimated λ, the population would reach extinction in 5 years; (2) an SDR outbreak as intense as the one observed in this study can lead to a notable decline in stochastic λs even when relatively rare (i.e. 10% probability of occurring); and (3) disease incidence as low as 5% can cause the population to lose its ecological functionality (e.g., reach a pseudo-extinction level of 10% of the initial population size) 33 years before disappearing. SDR and probably any other similarly virulent disease could thus be a major driver of local extinction events of A. cervicornis.
... While we attempted to maximize useable data through % Growth (alongside % Survivorship), our approach may still fail to fully capture how growth can equate to success. For example, new branches/tissue biomass may regulate how much of a colony can be harvested for restoration use (Mercado-Molina et al. 2016) but may not be accounted for in certain growth metrics (e.g. TLE; Lirman et al. 2014;Lohr et al. 2015). ...
Coral nursery and out‐planting practices have grown in popularity worldwide for targeted restoration of degraded “high value” reef sites, and recovery of threatened taxa. Success of these practices is commonly gauged from coral propagule growth and survival, which fundamentally determines the return‐on‐effort critical to the cost‐effectiveness and viability of restoration programs. In many cases, return‐on‐effort has been optimized from past successes and failures, which therefore presents a major challenge for locations such as the Great Barrier Reef (GBR) where no local history of restoration exists to guide best practice. In establishing the first multi‐taxa coral nursery on the GBR (Opal Reef, February 2018), we constructed a novel scoring criterion from concurrent measurements of growth and survivorship to guide our relative return‐on‐effort (RRE), including nursery propagule numbers (stock density). We initially retrieved RRE scores from a database of global restoration efforts to date (n=246; 52 studies) to evaluate whether and how success commonly varied amongst coral taxa. We then retrieved RRE scores for Opal Reef using initial growth and survivorship data for six key coral taxa, to demonstrate that RRE scores were high for all taxa predominantly via high survivorship over winter. Repeated RRE scoring in summer is therefore needed to capture the full dynamic range of success where seasonal factors regulating growth versus survivorship differ. We discuss how RRE scoring can be easily adopted across restoration practices globally to standardize and benchmark success, but also as a tool to aid decision‐making in optimizing future propagation (and out‐planting) efforts.
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... In the index x = 0 and x = 1 represent, respectively, the absence and the presence of branches within any given order, n equals the number of branches within a branch order, and k is the maximum order of branching (Carrillo-Mendoza et al. 2010). This index has previously been applied to describe the complexity of A. cervicornis colonies (Mercado-Molina et al. 2016). ...
The development of artificial corals using 3D-printing technology has been proposed as an alternative to aid the recovery of fish populations in degraded reefs. However, no study has empirically evaluated the potential of such artificial corals to attract fish to reef patches. We conducted an experiment to determine whether the number of fish associated with natural and 3D-printed corals differs significantly. The 3D-printed artificial corals mimicked the morphology of staghorn coral Acropora cervicornis, whose branches serve as habitat for many fish species. There is evidence indicating that fish abundance increases with habitat complexity, but no specific evidence relating to A. cervicornis. Therefore, we also investigated whether the structural complexity of both natural and artificial corals affected their effectiveness to attract fish. We found that the number of fish associated with artificial and natural corals was not significantly different. However, irrespective of coral type, fish were more abundant in corals with the highest levels of complexity. Our findings suggest that 3D-printed corals can serve as a complementary tool to improve the ecosystem function of degraded coral reefs. BACKGROUND
... Thereby, providing evidence that restoration and conservations efforts of these corals species should be focused on enhancing the probability of large colonies to survive. Mercado-Molina et al. [20,21] found that both growth and branching rates of A. cervicornis increase with size. Therefore, positive contribution of large colonies to λ, at least for A. cervicornis, can be partly explained by (1) a rapid growth that can allow the colony to reach a refuge size in which mortality associated with diseases, predation, and bleaching can be considerably reduced; and (2) an increase in the number of branches with the potential to be detached from the parental colony and become established as an independent colony, contributing to faster formation of thickets. ...
Low-tech coral farming and reef rehabilitation have become important tools to foster com-munity-based participation in the management of coastal social-ecological systems. Lessonslearned from coral demographic dynamics, ecosystem-level benefits, and sociologicaldynamics achieved in Culebra Island, Puerto Rico, are discussed. Important gaps regardingsocial-ecological interactions are also addressed. Coral reef rehabilitation efforts must beadaptive and focused on maximizing resilience as a long-term goal, with emphasis onmanaging non-linear dynamics, thresholds, environmental and climate uncertainty, andecological surprises. In this context, coral demographic modelling becomes fundamental toaddress, not only ecological, but also sociological concerns. Only through sustained supportand input of harvested corals restored populations, and by increasing the spatial scale of reefrehabilitation, restored populations can remain viable and grow under present and projec-ted environmental and climate conditions. Understanding sociological dynamics, learningfrom others experiences, integrating visioning and scenario building, leadership building,multi-sectorial agents and actor groups, and strengthening cross-sectorial social networkingare necessary adaptive approaches to cope with future environmental and climate changes,and are an integral part of reef rehabilitation. The combined benefits to social-ecologicalsystems are multiple. With proper planning, design, funding, local support, and implemen-tation, these can have long-lasting impacts in restoring coastal resilience.
Coral reefs, vital ecosystems supporting diverse marine life, are primarily shaped by the clonal expansion of coral colonies. Although the principles of coral clonal growth, involving polyp division for spatial extension, are well-understood, numerical modelling efforts are notably scarce in the literature. In this article, we present a parsimonious numerical model based on the cloning of polyps, using five key parameters to simulate a range of coral shapes. The model is agent-based, where each polyp represents an individual. The colony’s surface expansion is dictated by the growth mode parameter (s), guiding the preferred growth direction. Varying s facilitates the emulation of diverse coral shapes, including massive, branching, cauliflower, columnar and tabular colonies. Additionally, we introduce a novel approach for self-regulatory branching, inspired by the intricate mesh-like canal system and internode regularity observed in Acropora species. Through a comprehensive sensitivity analysis, we demonstrate the robustness of our model, paving the way for future applications that incorporate environmental factors, such as light and water flow. Coral colonies are known for their high plasticity, and understanding how individual polyps interact with each other and their surroundings to create the reef structure has been a longstanding question in the field. This model offers a powerful framework for studying these interactions, enabling a future implementation of environmental factors and the possibility of identifying the key mechanisms influencing coral colonies’ morphogenesis.
Coral nursery and outplanting practices have grown in popularity worldwide for targeted restoration of degraded “high value” reef sites, and recovery of threatened taxa. Success of these practices is commonly gauged from coral propagule growth and survival, which fundamentally determines the return‐on‐effort (RRE) critical to the cost‐effectiveness and viability of restoration programs. In many cases, RRE has been optimized from past successes and failures, which therefore presents a major challenge for locations such as the Great Barrier Reef (GBR) where no local history of restoration exists to guide best practice. In establishing the first multi‐taxa coral nursery on the GBR (Opal Reef, February 2018), we constructed a novel scoring criterion from concurrent measurements of growth and survivorship to guide our relative RRE, including nursery propagule numbers (stock density). We initially retrieved RRE scores from a database of global restoration efforts to date (n = 246; 52 studies) to evaluate whether and how success commonly varied among coral taxa. We then retrieved RRE scores for Opal Reef using initial growth and survivorship data for six key coral taxa, to demonstrate that RRE scores were high for all taxa predominantly via high survivorship over winter. Repeated RRE scoring in summer is therefore needed to capture the full dynamic range of success where seasonal factors regulating growth versus survivorship differ. We discuss how RRE scoring can be easily adopted across restoration practices globally to standardize and benchmark success, but also as a tool to aid decision‐making in optimizing future propagation (and outplanting) efforts.
Partial mortality is a common process affecting coral colonies. Yet, the impact of tissue loss on the demography of the threatened reef-building coral Acropora cervicornis has been poorly investigated. This limits our understanding of how this species will fare under unfavorable environmental conditions. In this study, we examined the growth and survival of colonies with varying degrees of partial mortality, indicated by tissue loss, for 2 yr at 2 reefs in Puerto Rico. We found that irrespective of colony size, rates of coral growth and survival declined significantly once the proportion of dead tissue exceeded 20% of the total colony size. Projections of state-matrix population models indicated that partial mortality could also have a negative impact at the population level. For instance, a 25% increase in the number of colonies with > 20% tissue loss would reduce the time in which 75% of the population is lost by 3 to 4 yr. Our results provide anew perspective on the effect of partial mortality on the demography and population dynamics of A. cervicornis. First, 20% of tissue loss can be considered a threshold value in which colony fate and population growth are compromised. Second, colony size is not the most important determinant of a colony’s demographic performance; instead, the surface area lost to partial mortality is abetter predictor of colony growth and survivorship. Taking into consideration the relationship between partial mortality and the demographic fate of A. cervicornis can aid in the development of stronger conservation and restoration program
In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region.
Paleontological data suggest that the regional Acropora kill is without precedent in the late Holocene. In Belize, A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon until the mid-1980s. After constructing reef framework for thousands of years, A. cervicornis was virtually eliminated from the area over a ten-year period. Evidence from other parts of the Caribbean supports the hypothesis of continuous Holocene accumulation and recent mass mortality of Acropora spp. Prospects are poor for the rapid recovery of A. cervicornis, because its reproductive strategy emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than A. cervicornis If the Acropora spp. do not recover, macroalgae will continue to dominate Caribbean reefs, accompanied by increased abundances of brooding corals, particularly Agaricia spp. and Porites spp. The outbreak of white-band disease has been coincident with increased human activity, and the possibility of a causal connection should be further investigated.
Populations of Acropora cervicornis have collapsed throughout the Caribbean. This situation has prompted the initiation of many restoration efforts; yet, there are insufficient demographic data and analyses to effectively guide these initiatives. In this study we assessed the spatiotemporal variability of A. cervicornis vital rates. We also developed a population matrix model to (1) evaluate the risk of population extinction, (2) estimate population growth rates (k) considering different rates of colony fragmentation and fragment survival, (3) determine the demographic transition(s) that contribute the most to spatiotemporal differences in ks, and (4) analyze the effectiveness of outplanting coral fragments of different sizes. The model was parameterized by following the fate of 300 colonies from 2011 to 2013 at two localities in Puerto Rico. Demographic transitions varied spatiotempo-rally, with a significant interaction between location and time period on colony fate. Spatiotemporal variations in k were also observed. During the first year, populations exhibited ks below equilibrium (0.918 and 0.948), followed by a dramatic decline at both sites (0.535 and 0.709) during the second year. The lower ks were caused by a decrease in the probability of stasis of large-sized colonies coupled with lack of sexual recruits and a meager contribution of asexual recruitment. Spatial variations in ks were largely due to differences in the probability of medium-sized colonies advancing to the largest size class. The viability analysis forecasts that the populations will reach quasi-extinction levels of 25 % of the initial population size in B16 yrs. Numerical simulations indicate that outplanting fragments C250 cm in total linear length (TLL) would result in a higher asymptotic population size than out-planting smaller fragments. We argue, however, that transplanting colonies B100 cm TLL will be a better management strategy because they can be produced faster and in higher numbers at coral nurseries.
The rapid decline of the staghorn coral Acropora cervicornis throughout the Caribbean prompted the development of coral gardening as a management strategy to restore wild stocks. Given that coral gardening relies on propagating corals collected from wild donor colonies, it is imperative to optimize growth within a nursery to reduce dependence on wild collections. This study determined the maximum amount of coral that may be clipped from a colony during propagation without causing mortality or decreased growth. We applied 3 experimental treatments to 12 nursery-reared staghorn corals, in which 25, 50, or 75% of the colony's total biomass was removed and fragmented to create additional, smaller fragments. Four additional colonies served as unfragmented controls. Treatment had no effect on colony productivity, defined as the ratio of new tissue growth to initial colony size, over 87 d. Similarly, treatment had no effect on the rate at which colonies developed new branches. Results indicate that 75% of the biomass of staghorn colonies may be removed without affecting their growth. We anticipate that our observations will have practical applications for maximizing propagation of staghorn coral within nurseries throughout the wider Caribbean while minimizing the impact of this management measure on remnant wild populations.
The mass mortality suffered by the sea urchin
Diadema antillarum
between 1983–1984 is considered one of the major causes of coral reef degradation in the Caribbean. Its near disappearance resulted in a disproportionate growth of macroalgae that has led to a ‘phase shift’ from coral-to-algal dominated reefs. The close relationship between this echinoid and the functioning of coral reef ecosystems makes it imperative to better understand the potential for recovery of its populations. From 2009 to 2011, we assessed the density and size structure of
D. antillarum
in various reefs where previous population data were available. Results indicate a modest increase in density in all localities with respect to the last time they were surveyed in 2003/2004. Nevertheless, density values are still lower than values reported for the island prior to the die-off. Overall density did not surpass 1.49 ind. per m
−2
, and did not change considerably during the studied period. Lack of population growth coincided with a lack of juveniles; suggesting that population growth at the studied sites may be limited by the number of individuals recruiting into the juvenile stage.
Trees without excessive branching are desirable for the reduction of pruning costs. Genetic diversity for less twiggy genotypes exists in peach and a branching index was developed for evaluation and selection of genotypes with reduced branching. The index is based on the number of total first-order branches and the number of second-order, third-order, and fourth-order branches measured on three randomly selected first-order branches. Index values were highly correlated (r2'0.7) with the total number of branches over two growing seasons and served as a good predictor of branching patterns observed in the third growing season. Thus, the developed branching index is a useful tool in peach breeding, allowing for the early selection of trees with more desirable tree architecture.
Coral reefs have largely declined across multiple spatial scales due to a combination of local-scale anthropogenic impacts, and due to regional-global climate change. This has resulted in a significant loss of entire coral functional groups, including western Atlantic Staghorn coral (Acropora cervicornis) biotopes, and in a net decline of coral reef ecosystem resilience, ecological functions, services and benefits. Low-tech coral farming has become one of the most important tools to help restore depleted coral reefs across the Wider Caribbean Region. We tested a community-based, low-tech coral farming approach in Culebra Island, Puerto Rico, aimed at adapting to climate change-related impacts through a two-year project to propagate A. cervicornis under two contrasting fishing management conditions, in coastal areas experimenting significant land use changes. Extreme rainfall events and recurrent tropical storms and hurricanes had major site-and method-specific impacts on project outcome, particularly in areas adjacent to deforested lands and subjected to recurrent impacts from land-based source pollution (LBSP) and runoff. Overall, coral survival rate in “A frame” units improved from 73% during 2011-2012 to 81% during 2012-2013. Coral survival rate improved to 97% in horizontal line nurseries (HLN) incorporated during 2012-2013. Percent tissue cover ranged from 86% to 91% in “A frames”, but reached 98% in HLN. Mean coral skeletal extension was 27 cm/y in “A frames” and 40 cm/y in HLN. These growth rates were up to 545% to 857% faster than previous reports from coral farms from other parts of the Caribbean, and up to 438% faster than wild colonies. Branch production and branchiness index (no. harvestable branches > 6 cm) increased by several orders of magnitude in comparison to the original colonies at the beginning of the project. Coral mortality was associated to hurricane physical impacts and sediment-laden runoff impacts associated to extreme rainfall and deforestation of adjacent lands. This raises a challenging question regarding the impact of chronic high sea surface temperature (SST), in combination with recurrent high nutrient pulses, in fostering increased coral growth at the expense of coral physiological conditions which may compromise corals resistance to disturbance. Achieving successful local management of reefs and adjacent lands is vital to maintain the sustained net production in coral farms and of reef structure, and the provision of the important ecosystem services that they provide. These measures are vital for buying time for reefs while global action on climate change is implemented. Adaptive community-based strategies are critical to strengthen institutional management efforts. But government agencies need to transparently build local trust, empower local stakeholders, and foster co-management to be fully successful. Failing to achieve that could make community-based coral reef rehabilitation more challenging, and could potentially drive rapidly declining, transient coral reefs into the slippery slope to slime.
Target fishery species have been traditionally used as indicators of compliance and management success in no-take marine protected areas (MPAs). However, this approach has the limitation of ignoring the effects that no-take MPAs may have on the functional role of fishes at the community and ecosystem levels. The first objective of this study was to document spatial and temporal variation patterns in the structure of coral reef fish communities at the functional group level within the Luis Peña Channel No-Take Natural Reserve (LPCNR) in Culebra Island, Puerto Rico. The second objective was to test the efficiency of fish functional groups as indicators of management success in the LPCNR. There was a rapid recovery of fish communities three years follow-ing the designation of the LPCNR in 1999. Fish communities at a control fished reef located outside the reserve boundaries also showed a rapid recov-ery. However, management failures have resulted in poor compliance and in a recent increase in illegal fishing activities. This has resulted in a fish decline trend within core areas of LPCNR during the period of 2002 to 2004. Control sites showed the opposite trend. Also, fish communities at the reserve boundary site collapsed as a combined result of increased fishing pressure by fishers displacement after LPCNR designation and by chronic environmental degradation from areas outside reserves boundaries (i.e., large volumes of sediment-and nutrient-loaded runoff, raw sewage discharges). Chronic environmental degradation between 1997 and 2003 has been associated to a major phase shift in the community structure of coral reef benthic communities from coral to algal dominance within LPCNR. In spite of that, LPCNR has been a successful tool restoring overexploited fish communities in Culebra Island. This suggests that even with very limited efforts no-take MPAs can be successful in restoring severely depleted fishery resources. However, manage-ment failures within and outside LPCNR need to be addressed and eliminated in order to keep community support, and to restore trust and compliance.
Coral reef restoration has gained recent popularity in response to the steady decline of corals and the recognition that coral reefs may not be able to recover naturally without human intervention. To synthesize collective knowledge about reef restoration focused particularly on the threatened genus Acropora in the Caribbean and western Atlantic, we conducted a literature review combined with personal communications with restoration practitioners and an online questionnaire to identify the most effective reef restoration methods and the major obstacles hindering restoration success. Most participants (90%) strongly believe that Acropora populations are severely degraded, continue to decline, and may not recover without human intervention. Low-cost methods such as coral gardening and fragment stabilization were ranked as the most effective restoration activities for this genus. High financial costs, the small footprint of restoration activities, and the potential damage to wild populations were identified as major concerns, while increased public awareness and education were ranked as the highest benefits of coral reef restoration. This study highlights the advantages and outlines the concerns associated with coral reef restoration and creates a unique synthesis of coral restoration activities as a complementary management tool to help guide “best-practices” for future restoration efforts throughout the region.
Gobiid fishes of the genus Gobiodon live in strong association with certain reef-building corals that vary considerably in size and architecture. These fishes hence are excellent model systems for studying evolutionary adaption to specific microhabitats. Using a sample of Gobiodon histrio and G. rivulatus and their most important host corals (Acropora digitifera and A. gemmifera) from the northern Red Sea, we assess (1) how corals that are occupied by gobies differ in their architecture from colonies that are not occupied and (2) how fish body shape is associated with the architecture of their host coral. Fish body shape was assessed by geometric morphometric techniques. Coral measurements included colony size, branch length (BL), and interbranch as well as branch tip distance of adjacent branches, for which we applied a new and non-destructive measurement technique based on casts of two-component epoxy resin. The most important factor influencing the occupation of corals was a BL of more than 5 cm. The distance between coral branches was clearly related to the width of the fishes and hence constrained overall fish size. G. histrio and G.
rivulatus differ in adult body shape as well in their allometric development of lateral body compression, resulting in different maximum body sizes attainable in the restricted interbranch space of corals. The strong dependence of coral-associated fishes on large coral colonies with specific architectures increases the extinction risk of fishes within deteriorating coral reefs.
Shallow water Acropora species have become uncommon on north coast Jamaican coral reefs owing to a number of factors. On many reefs, algae have taken their place. The result is loss of habitat for many spe- cies of fish and invertebrates and less attractive reefs with fewer fish. These reefs appear to be prime candidates for coral restoration. However, the potential for coral to naturally recover should be examined before efforts to restore reefs are undertaken. Reef restoration is unnecessary if the population has the capacity to recovery through natural means. We observed that the rate of settlement of Acropora spat in the Caribbean is much lower than the spat settlement rate of several other Caribbean coral families and much lower than Acropora spat settle- ment rates in the South Pacific. A very low percentage of apparently healthy colonies of A. cervicornis possessed developing gametes in July 2005, a month before spawning. It appears that the long-term survival of remnant A. cervicornis populations is threatened unless successful sexual reproduction is restored. Several techniques were used to test transplant methods for restoring A. cervicornis populations. The mean survivorship and growth rate of one technique was >75% and nearly 250% per annum, respectively. Working with hotel operators, environ- mental groups, and local fishers, we are attempting to reintroduce A. cervicornis to sites where it previously existed and increase coral biomass and complexity at these sites. Reefs with greater A. cervicornis biomass have larger edible fish populations. With localized protection of these restored reefs we anticipate an increase of larger edible fish not only on reefs within the restored protected areas but also on adjacent reefs. Furthermore, increased coral and fish biodiversity improves the attractiveness of the reef community for divers and snorkelers. Rev. Biol. Trop. 54 (Suppl. 3): 105-116. Epub 2007 Jan. 15.
Morphological plasticity is common among clonal organisms, including scleractinian corals, yet the role of phenotypic plasticity in coral ecology and evolution is largely unexplored. Additionally, it is unclear how much variation in plastic responses exists among individuals, populations, and species, and thus how much potential there is for natural selection to act on coral reaction norms. In the branching coral Madracis mirabilis, corallite architecture and density, branch diameter and spacing, and overall aggregate morphology all vary among environments. To examine the role of phenotypic plasticity in generating these patterns, clonal replicates of five genotypes of M. mirabilis were transplanted from each of two source populations into four treatment environments on the north coast of Jamaica. Flow rate, sedimentation, irradiance, water temperature, and salinity all varied among these environments. DNA fingerprinting was used to ensure that the 10 transplanted genotypes were genetically distinct. Six morphological traits (intersepta area, septa length, columella area, corallite area, corallite spacing, and branch tip diameter) were measured after transplantation to determine whether they were altered in response to environmental conditions. Because these traits were correlated, principal components analysis was used to define new, uncorrelated traits for analysis. Four of the five corallite traits and branch diameter were significantly affected by the environment, demonstrating that morphological variation among environments in M. mirabilis is due in large part to phenotypic plasticity. No difference was detected between the two source populations in the magnitude or direction of their plastic responses, but there was substantial variation among genotypes (genotype x environment interaction). Many of the phenotypic changes of both populations resulted in the transplants becoming morphologically similar to resident conspecifics in each treatment environment. Genotypes from both populations were able to maintain similar growth rates under diverse environmental conditions. Such morphological convergence by phenotypic plasticity may expand the ecological range of this species by enabling genotypes to tolerate spatially and temporally variable environments.
Our objective was to provide a baseline data bank of the ecological conditions of the proposed Culebra Island's Marine Fishery Reserve (MFR). Aerial photographs were analyzed using dot grids to determine the percent coverage of bottom communities. We used line intercept transects to quantitatively describe coral reef epibenthic communities and stationary visual censuses to quantitatively describe fish communities. With these data we calculated the following community parameters: species richness, abundance, Shannon-Weaver Index (H'n), evenness (J'n), % of coral cover, total biomass and standing stock biomass. Bootstrapping analysis was used to test for significant differences in the average values of these parameters between sampling stations and years. Seagrass beds were the most abundant community type (35%), followed by coral reefs (34%), sandy bottoms (11%) and hard grounds (10%). A total of 69 coral species were identified, including 4 hydrocorals, 25 octocorals and 40 scleractinians. Epibenthic surveys showed that there were no significant changes in species richness, H'n, and J'n between 1997 and 1998 in sampling stations CR1 and CR2. There was a non- significant increase in colony abundance between 1997 and 1998 mostly due to partial coral tissue mortality and its consequent colony fragmentation. Only 29% of the hard corals were considered to be healthy, 46% were overgrown by filamentous algae, 37% by macroalgae and 20% were bioeroded. Coral mortality was estimated to be 32.9±5.6% at CR1 and 28.3±9.8% in CR2 for the 1998 data. A total of 221 fish species were identified, including 113 genera and 59 families. Fish surveys demonstrated no significant changes in the fish community of the Carlos Rosario Beach between 1996 and 1998. But, there were significant differences between Carlos Rosario Beach and Cayo de Luis Peña. The latter showed significantly higher average values in fish abundance, total biomass, standing stock biomass, and biomass and density of fishery target species. Our data indicate that the proposed MFR has a high coverage of critical habitats, high diversity of corals and fishes, and that fish populations are very healthy in parts of the proposed reserve. Cayo de Luis Peña is less accessible to spearfishermen than Carlos Rosario Beach, which suggest that there is a severe overfishing problem in the latter locality. We recommend to the government of Puerto Rico to take action
Coral mortality has increased in recent decades, making coral recruitment
more important than ever in sustaining coral reef ecosystems and contributing to their
resilience. This review summarizes existing information on ecological factors affecting
scleractinian coral recruitment. Successful recruitment requires the survival of coral offspring
through sequential life history stages. Larval availability, successful settlement,
and post-settlement survival and growth are all necessary for the addition of new coral
individuals to a reef and ultimately maintenance or recovery of coral reef ecosystems. As
environmental conditions continue to become more hostile to corals on a global scale,
further research on fertilization ecology, connectivity, larval condition, positive and negative
cues infl uencing substrate selection, and post-settlement ecology will be critical to
our ability to manage these diverse ecosystems for recovery. A better understanding of
the ecological factors infl uencing coral recruitment is fundamental to coral reef ecology
and management.
Corals and macroalgae compete for space, but the influence of species and size on the competitive outcome is poorly understood. Using a manipulative experiment, we evaluated the effect of macroalgal competition on the growth rate of corals with an emphasis on the colony size, species identity and the intensity of competition. Coral-macroalgal competition was studied among 3 Caribbean coral species (Porites astreoides, Agaricia agaricites and Colpophyllia natans) and 2 macroalgal species (Lobophora variegata and Halimeda opuntia) for 1 yr. Two coral colony sizes were used and, for the smaller size class, 2 levels of intensity for macroalgal competition (25 and 100% contact with the coral perimeter). Coral size had the greatest effect on competitive outcome; 2 species of large corals under competition grew as much as controls and a third species did not lose tissue. All small colonies lost between 18 and 22% of their original area after a year of competing with macroalgae, and the competitive outcome was insensitive to algal species. Coral colony size is a critical factor for the competitive outcome with algae and the intensity of contact between competitors is not important in smaller corals. In general, our results support the theory that algal blooms can inhibit coral population dynamics by causing a bottleneck in the survivorship of smaller size classes.
A mass mortality event of the long-spined sea urchin Diadema antillarum (Philippi, 1845) occurred during 1983-1984 across the western Atlantic. Recovery to pre-mortality densities has been slow throughout most of the Caribbean as current stocks remain low, existing at a small fraction of previously recorded levels. To measure population recovery at Puerto Rico, we surveyed 26 localities around the island during 2003-2004. At each reef, we deployed 15 × 2 m belt transects (n = 12) to detect and quantify the presence of D. antillarum and obtain data on benthic cover. Density of D. antillarum varied significantly among geographic regions and localities, though variability was high. The highest density was documented in the Culebra Island region (0.44 ind m−2), followed by the northern region of Puerto Rico (0.23 ind m−2). No individuals of D. antillarum were found in 11 of the 26 surveyed localities. These densities are still substantially lower than pre- and post-mortality estimates from Puerto Rico. Most of the reefs were characterized by high macroalgal cover and horizontal water transparency < 3 m. Urchin densities were significantly and positively correlated with percentage of coral cover, percentage of coralline algae, and water transparency.
The whole-colony morphology of the coral, Porites sillimaniani, varies dramatically in accordance with light intensity from plate-like shape to branching shape. To determine whether the variation is based on genetic difference or phenotypic plasticity, we conducted a field experiment by transplanting coral fragments taken from seven plate-like colonies to different light conditions. The fragments that transplanted to the high-light condition started to have branches in 8 mo period of the experiment, whereas those to the low-light condition remained to be flat. This result suggests that the morphological variation is the phenotypic plasticity in response to light availability. To examine the adaptive significance of this plasticity, a simple mathematical model of coral shape is constructed, in which the number of branches, their angles and lengths are morphological parameters. The circumference of the model coral is assumed to be uniformly covered with polyps. Each polyp survives if its light flux is larger than a certain threshold value. The optimal morphology that can support a maximum number of viable polyps is calculated for a given light intensity. The optimal coral shape changes with light intensity, which agrees qualitatively with the observation of P. sillimaniani colony in natural habitats.
Low-cost and environmentally sustainable coral reef restoration methods modeled after natural coral reef recovery processes and appropriate for use in developing countries were investigated. The study focused on post-fragmentation processes important to natural coral reef recovery and to successful transplantation, quantifying size-specific, substrate-specific, site-specific, and species-specific survival, growth, and self-attachment of coral fragments. Acropora cervicornis and A. prolifera, with distinct morphotypes from high and low energy environments were used for all experiments. Coral fragments of similar size from axial and basal regions were also tested to determine if senescence affects survival. Results indicate that the mortality and growth of unattached coral fragments are strongly size and substrate dependent, with insignificant differences between morphotypes, species, and sites. Axial fragments had significantly lower mortality than did inner/older fragments. Back reef and reef front morphotypes of A. cervicornis grown together in the sheltered back reef for 1 yr continued to differ significantly in branch diameter, relative growth, and self-attachment ability, indicating a genetic basis to morphology and adaptation to specific reef environments. Scattering coral fragments onto unstable rubble or attaching fragments to simple frames on sand proved effective for restoring coral cover to substrates where natural larval-based recruitment processes are inhibited.
Restoration of rare corals is desirable and restoration projects are fairly common, but scientific evaluation of this approach is limited. We tested several techniques for transplant and restabilization of Acropora palmata (the elkhorn coral), an ecologically important Caribbean coral whose populations have suffered severe declines. In rough weather, fragments break-off colonies of branching corals like A. palmata as a normal form of asexual reproduction. We transplanted naturally produced coral fragments from remnant populations to nearby restoration sites. Untouched control fragments at the donor site died faster and grew slower than fragments attached to the reef, so attaching fragments to the reef is beneficial. Transplanted fragments grew and died at a rate similar to fragments left at the donor site (both groups were attached to the reef), so there were no effects of moving fragments or differences in habitat quality between donor and restoration sites. Growth and survival were similar using four methods of attaching fragments to the reef: cable ties, two types of epoxy resin, and hydrostatic cement. Corals sometimes compete with the macroalgae that dominate degraded reefs, and clearing surrounding algae improved the growth of fragments. After 4 years, transplanted fragments grew to 1,450 cm2 in area and so were potentially sexually active. Because the methods tested are simple and cheap, they could be used by volunteer recreational divers to restore locally extirpated A. palmata populations or to enhance reefs where natural recovery is slow.
In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region.
Paleontological data suggest that the regional Acropora kill is without precedent in the late Holocene. In Belize, A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon until the mid-1980s. After constructing reef framework for thousands of years, A. cervicornis was virtually eliminated from the area over a ten-year period. Evidence from other parts of the Caribbean supports the hypothesis of continuous Holocene accumulation and recent mass mortality of Acropora spp. Prospects are poor for the rapid recovery of A. cervicornis, because its reproductive strategy emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than A. cervicornis. If the Acropora spp. do not recover, macroalgae will continue to dominate Caribbean reefs, accompanied by increased abundances of brooding corals, particularly Agaricia spp. and Porites spp. The outbreak of white-band disease has been coincident with increased human activity, and the possibility of a causal connection should be further investigated.
Along the northeastern Gulf of Mexico coast, Leptogorgia hebes is the predominant gorgonian at two inner shelf (22 and 27 m) sites, while Leptogorgia virgulata dominates a third shallow (1–2m), inshore site. The axial skeleton of both species is composed of concentric rings which appeared to exhibit annual periodicity. Although age structure of the populations differed between shelf sites, neither colony growth rates, estimated from direct measurements of ring widths plotted on Walford graphs, nor overall branching complexity, determined from bifurcation ratios (Rb), differed between the shelf populations. Larger individuals at the 27m shelf site were simply older than those at the shallower (22m) shelf site. Walford plots of growth increments revealed colony growth of the shallow inshore species to be similar to that of the offshore species.
The Caribbean reef-building corals Acropora palmata and Acropora cervicornis have undergone widespread declines in the past two decades, leading to their designation as candidates for listing under the United States Endangered Species Act. Whole-reef censuses in 1983 and 2000 at Looe Key National Marine Sanctuary in the Florida Keys provide estimates of areal loss of live Acropora spp. cover. Area (square meters) of live coral cover was quantified from depiction on scaled base maps of extent of coral cover observed by a snorkeler on each reef spur at each census. Certain thickets appear to have been persistent (though none expanded), but the total area of live A. palmata at Looe Key is estimated to have declined by 93% and A. cervicornis by 98% during this 17-year interval. It is likely that acroporid populations may have already undergone substantial decline prior to our initial census in 1983.
Despite the universality of branching patterns in marine modular colonial organisms, there is neither a clear explanation about the growth of their branching forms nor an understanding of how these organisms conserve their shape during development. This study develops a model of branching and colony growth using parameters and variables related to actual modular structures (e.g., branches) in Caribbean gorgonian corals (Cnidaria). Gorgonians exhibiting treelike networks branch subapically, creating hierarchical mother-daughter relationships among branches. We modeled both the intrinsic subapical branching along with an ecological-physiological limit to growth or maximum number of mother branches (k). Shape is preserved by maintaining a constant ratio (c) between the total number of branches and the mother branches. The size frequency distribution of mother branches follows a scaling power law suggesting self-organized criticality. Differences in branching among species with the same k values are determined by r (branching rate) and c. Species with r<c had a sigmoid logistic-like growth with a long asymptotic period before reaching k. Gorgonians exhibit c and r values in the range of the conditions for a stable equilibrium (c>r/2 or c>r>0). Ecological/physiological constraints limit growth without altering colony form or the interaction between r and c. The model described the branching dynamics giving the form to colonies and how colony growth declines over time without altering the branching pattern. This model provides a theoretical basis to study branching as a simple function of the number of branches independently of ordering- and bifurcation-based schemes.
Colonial invertebrates such as corals exhibit nested levels of modularity, imposing a challenge to the depiction of their morphological evolution. Comparisons among diverse Caribbean gorgonian corals suggest decoupling of evolution at the polyp vs. branch/internode levels. Thus, evolutionary change in polyp form or size (the colonial module sensu stricto) does not imply a change in colony form (constructed of modular branches and other emergent features). This study examined the patterns of morphological integration at the intraspecific level. Pseudopterogorgia bipinnata (Verrill) (Octocorallia: Gorgoniidae) is a Caribbean shallow water gorgonian that can colonize most reef habitats (shallow/exposed vs. deep/protected; 1-45 m) and shows great morphological variation.
To characterize the genotype/environment relationship and phenotypic plasticity in P. bipinnata, two microsatellite loci, mitochondrial (MSH1) and nuclear (ITS) DNA sequences, and (ITS2) DGGE banding patterns were initially compared among the populations present in the coral reefs of Belize (Carrie Bow Cay), Panama (Bocas del Toro), Colombia (Cartagena) and the Bahamas (San Salvador). Despite the large and discrete differentiation of morphotypes, there was no concordant genetic variation (DGGE banding patterns) in the ITS2 genotypes from Belize, Panama and Colombia. ITS1-5.8S-ITS2 phylogenetic analysis afforded evidence for considering the species P. kallos (Bielschowsky) as the shallow-most morphotype of P. bipinnata from exposed environments. The population from Carrie Bow Cay, Belize (1-45 m) was examined to determine the phenotypic integration of modular features such as branch thickness, polyp aperture, inter-polyp distance, internode length and branch length. Third-order partial correlation coefficients suggested significant integration between polypar and colonial traits. Some features did not change at all despite 10-fold differences in other integrated features. More importantly, some colonial features showed dependence on modular features.
Consequently, module integration in gorgonian corals can be shifted, switched or canalized along lineages. Modular marine organisms such as corals are variations on a single theme: their modules can couple or decouple, allowing them to adapt to all marine benthic environments.
Phenotypic plasticity enables multicellular organisms to adjust morphologies and various life history traits to variable environmental challenges. Here, we elucidate fixed and plastic architectural rules for colony astogeny in multiple types of colonial ramets, propagated by cutting from genets of the branching coral Stylophora pistillata from Eilat, the Red Sea. We examined 16 morphometric parameters on 136 one-year old S. pistillata colonies (of seven genotypes), originating from small fragments belonging, each, to one of three single-branch types (single tips, start-up, and advanced bifurcating tips) or to structural preparative manipulations (representing a single or two growth axes). Experiments were guided by the rationale that in colonial forms, complexity of evolving phenotypic plasticity can be associated with a degree of structural modularity, where shapes are approached by erecting iterative growth patterns at different levels of coral-colony organization. Analyses revealed plastic morphometric characters at branch level, and predetermined morphometric traits at colony level (only single trait exhibited plasticity under extreme manipulation state). Therefore, under the experimental manipulations of this study, phenotypic plasticity in S. pistillata appears to be related to branch level of organization, whereas colony traits are controlled by predetermined genetic architectural rules. Each level of organization undergoes its own mode of astogeny. However, depending on the original ramet structure, the spherical 3-D colonial architecture in this species is orchestrated and assembled by both developmental trajectories at the branch level, and traits at the colony level of organization. In nature, branching colonial forms are often subjected to harsh environmental conditions that cause fragmentation of colony into ramets of different sizes and structures. Developmental traits that are plastic, responding to fragment structure and are not predetermine in controlling astogeny, allow formation of species-specific architecture product through integrated but variable developmental routes. This adaptive plasticity or regeneration is an efficient mechanism by which isolated fragments of branching coral species cope with external environmental forces.
Measurements of Acropora cervicornis branching morphology from a low-energy back-reef area and an adjacent higher energy reef crest demonstrate that with this lateral increase in water energy morphology changes so that: 1) inclination of all branch orders to horizontal decreases; 2) branch orientations with tips pointing away from oncoming flow become dominant; and 3) 'bushiness' of amount of branching increases. -from Author
Colony architecture in branching colonial organisms is established through iterated processes of the structural units (modules), both zooids and the branches. Different approaches to analyzing colonial organization have revealed an intrinsic order to branched forms. By using mathematical models such as fractals, simulations of diffusion and flow, applying tree architectural models and developmental canalization ideas or analyzing heterochrony, attempts have been made to mimic the rules of colony formation. However, most approaches have not prioritized the rationale that structures and rules which govern the way a branching organism is built are heritable characteristics, and that even phenotypic plasticity is the expressed outcome of plasticity genes. There is no model system yet for the study of genetic impact on the architecture of branching modular organisms. Stylophora pistillata, an Indo-Pacific hermatypic coral, is treated here as such a model. S. pistillata morphometric characters are then analyzed. I raise the possibility that genetics is a key factor in shaping colony landscape and that genetic factors should be considered when studying the architecture of marine branching forms.
The percentage hypsometric curve (area-altitude curve) relates horizontal cross-sectional area of a drainage basin to relative elevation above basin mouth. By use of dimensionless parameters, curves can be described and compared irrespective of true scale. Curves show distinctive differences both in sinuosity of form and in proportionate area below the curve, here termed the hypsometric integral. A simple three-variable function provides a satisfactory series of model curves to which most natural hypsometric curves can be fitted. The hypsometric curve can be equated to a mean ground-slope curve if length of contour belt is taken into account. Stages of youth, maturity, and old age in regions of homogeneous rock give a distinctive series of hypsometric forms, but mature and old stages give identical curves unless monadnock masses are present. It is therefore proposed that this terminology be replaced by one consisting of an inequilibrium stage, an equilibrium stage, and a monadnock phase. Detailed morphometric analysis of basins in five sample areas in the equilibrium stage show distinctive, though small, differences in hypsometric integrals and curve forms. In general, drainage basin height, slope steepness, stream channel gradient, and drainage density show a good negative correlation with mean integrals. Lithologic and structural differences between areas or recent minor uplifts may account for certain curve differences. Regions of strong horizontal structural benching give a modified series of hypsometric curves. Practical applications of hypsometric analysis are foreseen in hydrology, soil erosion and sedimentation studies, and military science.
Three areas of Discovery Bay were studied. Acropora cervicornis was abundant on the haystacks of the west fore reef between 5-20 m depth where up to 11 corals per m2 produced a maximum of 10 m of branches. Here the individual corals were significantly larger than those of the east fore reef or the back reef. Although a significant negative correlation of growth rate with depth (cm yr-1 = 14.46 - 0.19 (depth, m)) was found on the west fore reef, the shallow corals were not taller but rather showed a higher level of branching. The major predators are a sea urchin, damselfish, a snail and a polychaete. Clinoid sponges are abundant in the coral skeleton. There is a large contribution by A. cervicornis to the skeletal calcium carbonate of the reef, and thus to vertical reef accumulation; this study estimates 1.4 kg m- 2 yr-1 in the cervicornis zone. The success of A. cervicornis derived primarily from its ability to regenerate from fragments. It exerts a competitive dominance over other space-occupiers by virtue of its high growth rate, a pronounced shading effect, mechanical damage to underlying corals through its breakage, and a seasonal recruitment to available spaces by fragmentation. -from Author
Reproductive characters of the Caribbean reef-building coral Acropora cervicornis were investigated based on histological samples collected from April 2001 through October 2002. Oogenesis commenced in early to mid-October through November and spermatogenesis was initiated from January to March. The onset of gametogenesis was staggered, exhibiting up to approximately a 1-month delay within colonies. In the hermaphroditic polyps, the observed male-to-female gonad ratio was nearly 1:1 and ripe oocytes represented over 70% of the total gonadal volume. Fecundity estimates based on Stage IV ova ranged between 10.4 and 21.8mm3 per square centimeter per year, comparable to A. cervicornis in Puerto Rico and other broadcasting Indo-Pacific Acropora. Fecundity estimates based on Stage III vitellogenic oocytes indicated statistically significant differences among study sites. Spawning in field conditions was observed in 2001, 2003, and 2004 from 2300 to 2330h. Gamete release generally occurred synchronously between nights two and seven after the full moon of July or August. However in 2003, multiple, small-scale gamete release episodes occurred over more than one lunar cycle. This coincided with the full moon occurring early in the month of July. While prolific gamete production is reported in this study, low levels of recruitment have been reported for this species. Thus, the highly fragmenting A. cervicornis may rely heavily on asexual reproduction for population maintenance and expansion, and recovery after disturbance may be greatly protracted.
Geomorphological methods for quantifying branching networks are used to describe inter- and intra-specific differences in branching patterns among two species of arborescent Caribbean gorgonian, Plexaura homomalla, P. flexuosa, and a third, undescribed plexaurid from the San Blas Islands, Panama. There were significant differences among species for first, second and third order branch lengths, and for tributary to source ratios for first and second order branches. Extrapolations from the branching parameters successfully predicted differences in the branch structure of naturally generated colony fragments. Within P. homomalla, significant differences with depth in the lengths and tributary to source ratios of first, second, and third order branches provide a measure of the greater bushiness of shallow water colonies. These measures can be used to quantify morphological differences in both ecological and systematic analyses. Data on the branching characters of these three gorgonian species demonstrate that gross colony form can be studied as a quantifiable component of phenotype and that gorgonians display both species level and ecophenotypic variation in colony form.
The role of microhabitat in structuring epifaunal communities on four corals of varying morphology in the genus Acropora (A. millepora, A. hyacinthus, A. pulchra, A. formosa) was determined on two fringing reefs in the central Great Barrier Reef. Greater abundance and species richness of epifauna on tightly branched coral species in comparison to their rarity or absence on open-branched species suggests that protection afforded by complex habitats is important in structuring coral epifaunal communities. Within species, neither total colony space nor live surface area of corals was correlated with either the abundance or species richness of associated epifauna. However, space between branches significantly affected the size of Tetralia crabs associated with different coral species. Patterns in the size distribution of Tetralia on two species of Acropora suggest that crabs select coral hosts according to branch spacing, changing host species as they grow larger.
Coral reefs throughout the world are under severe challenges from many environmental factors. This paper quantifies the size structure of populations and the growth rates of corals from 2000 to 2008 to test whether the Discovery Bay coral colonies showed resilience in the face of multiple acute stressors of hurricanes and bleaching. There was a reduction in numbers of colonies in the smallest size class for all the species at all the sites in 2006, after the mass bleaching of 2005, with subsequent increases for all species at all sites in 2007 and 2008. Radial growth rates (mm yr(-1)) of non-branching corals and linear extension rates (mm yr(-1)) of branching corals calculated on an annual basis from 2000-2008 showed few significant differences either spatially or temporally. At Dairy Bull reef, live coral cover increased from 13+/-5% in 2006 to 20+/-9% in 2007 and 31+/-7% in 2008, while live Acropora species increased from 2+/-2% in 2006 to 10+/-4% in 2007 and 22+/-7% in 2008. These studies indicate good levels of coral resilience on the fringing reefs around Discovery Bay in Jamaica.
Populations of the staghorn coral, Acropora cervicornis, often form dense monotypic stands on shallow Caribbean reefs. This coral species has a fragile structure that results in large numbers of broken branches and toppled colonies, especially in high wave activity. Although more than 80% of the corals in the studied population were broken from their bases, most had become reanchored to regrow rapidly. There is little evidence of sexual reproduction, and it appears that this coral has come to dominate much of the Jamaican reef community by propagation through fragmentation.
The architecture of the colony in a branching coral is an iterative process in which new layers of calcium carbonate compile atop existing structures that remain unchanged. Colony growth and development, known as astogeny, is believed to be a continuous process, characterized by replication of lower rank unites, polyps, and branches. This study seeks to explore the genetic blueprint of branch-to-colony developmental trajectory in the branching coral Stylophora pistillata, within an astogeny period of 1 year. One hundred small branches (initially 2-4 cm long) were sampled from 10 colonies. A year later, 63 remaining colonies were analyzed for their architectural rules by using 15 morphometric parameters. Multivariate statistical tests were preformed. Cluster and two-dimensional nonmetric Multi-Dimensional Scaling analyses revealed that the 10 genotypes could be divided into two major morphometric groups and two intermediate groups, whereas SIMPER analyses (a similarity percentage test) on within-genet similarities showed high similarity between the ramets developed from each of the 10 genotypes. Although, at first, it seemed that different colonies exhibited variable and different architectural designs (each characterized by specific morphometric parameters), a comprehensive analysis revealed that all 10 coral genotypes exhibited a single common developmental plan that was characterized by a continuum of architectural design with several distinct stages. Each stage is marked by its own characteristic morphometric parameters. Changing of developmental rules during the trajectory from branch to coral colony may help the colony to cope better with environmental constraints.
Proceedings of the Caribbean Acropora Workshop: potential application of the US Endangered Species Act as a conservation strategy
- Bruckner
Bruckner, A.W., 2003. Proceedings of the Caribbean Acropora Workshop: potential application of the US Endangered Species Act as a conservation strategy. NOAA Tech
Memo NMFS OPR-24:184.
Translocation of Acropora cervicornis across Geographic Regions: Investigating Species Recovery and Restoration
- B C Bliss
Bliss, B.C., 2015. Translocation of Acropora cervicornis across Geographic Regions: Investigating Species Recovery and Restoration. Nova Southeastern University, Master's thesis (91 pp.).
Caribbean staghorn coral populations: Pre-Hurricane Allen conditions in Discovery Bay, Jamaica
- Tunnicliffle