Comparative demography of two common scleractinian corals:Orbicella annularisandPorites astreoides (original) (raw)
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Background: Studies directed at understanding the demography and population dynamics of corals are relatively scarce. This limits our understanding of both the dynamics of coral populations and our capacity to develop management and conservation initiatives directed at conserving such ecosystems. Methods: From 2012 to 2014, we collected data on the growth, survival, and recruitment rates of two common Caribbean coral species, the stress-tolerant Orbicella annularis and the weedy Porites astreoides. A set of size-based population matrix model was developed for two localities in Northeastern Puerto Rico and used to estimate population growth rates () and determine the life cycle transition(s) that contribute the most to spatiotemporal differences in s. The model was parameterized by following the fate of 100 colonies of each species at the two sites for two years. Results: Our data indicate that spatial variability in vital rates of both species was higher than temporal variability. During the first year, populations of O. annularis exhibited s below equilibrium at Carlos Rosario (0.817) and Palomino (0.694), followed by a considerable decline at both sites during the second year (0.700 and 0.667). Populations of P. astreoides showed higher s than O. annularis during the first census period at Carlos Rosario (0.898) and Palomino (0.894) with a decline at one of the sites (0.681 and 0.893) during the second census period. Colony fate in both species exhibited a significant interaction with respect to location but not to time (G2 = 20.96; df = 3 for O. annularis and G2 = 9.55; df = 3 for P. astreoides). Discussion: The similar variability of s as well as the similar survival rates for both species during the two-year census period (2012–2014) show similar variability on demographic patterns in space and time. Our results suggest that location rather than time is important for the resiliency in coral colonies. Also, P. astreoides will show higher resistance to disturbance in the future than O. annularis.
Coral populations in a rapidly changing environment
Journal of Experimental Marine Biology and Ecology
Contemporary coral populations are being forced to survive through disturbances at a variety of spatial and temporal scales. Understanding disturbances in the context of ecological processes may lead to models that accurately predict population trajectories. Few studies examine the key ecological processes that drive changes on reefs. Processes of major interest include reproduction, recruitment, post-settlement mortality, coral growth, fragmentation, and mortality. These population processes are dependent on macro-processes, such as predation and herbivory, which in turn vary in accordance with regional oceanography. Some coralreef regions experience high-frequency temperature anomalies, whereas other regions experience lowfrequency anomalies. It may turn out that corals in the high-frequency regions are also most likely to undergo rapid directional selection, and adapt to climate change, because only alleles experiencing persistent selection pressure may attain high frequency. Yet corals are clonal organisms and the same genotypes are often exposed to different environments and to different selective pressures. Therefore, when comparing coralpopulation trajectories across regions and oceans, it is critical to understand the key processes of corals within local, regional, and historical contexts.
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 themost to spatiotemporal differences inks, 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 spatiotemporally, with a significant interaction between location and time period on colony fate. Spatiotemporal variations in population growth were also observed. During the first year, populations exhibited population growth 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 population growth 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 16 yrs. Numerical simulations indicate that outplanting fragments 250 cm in total linear length (TLL) would result in a higher asymptotic population size than outplanting 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.
Marine Ecology Progress Series, 2007
We compared the population structure of 8 common coral species in 2 contrasting habitats, the oceanic fringing reefs and the inland bays in Curaçao, Netherlands Antilles. Inland bays are only partially connected to the open ocean and are characterized by a natural suite of environmental factors thought to be detrimental to coral community development. Compared with the inland bays, coral cover and coral colony density were higher on the fringing reefs (7.6 and 11.7 times, respectively). Coral species that release gametes in the water column ('broadcast spawners') showed a much greater difference in population structure and density between inland bay and reef habitats compared to brooding species. Our results show that (1) 'marginal' habitats are not equally marginal to all species, (2) differential susceptibility to partial mortality plays a central role in restricting colony growth in inland bay habitats, and (3) most likely, post-settlement mortality rather than larval supply plays a key role in causing differences in habitat-scale size-frequency distributions. Broadcasting species reached larger mean and maximum colony size on the fringing reefs, whereas brooders did not show this pattern. The overrepresentation of large colonies in communities that had degraded in response to anthropogenic disturbance was not observed among coral populations in inland bays. Such characteristics deserve critical attention, as they can be used to distinguish between naturally and anthropogenically stressed Caribbean coral communities.
Inferring demographic processes from population size structure in corals
Analysis of coral population size structure is difficult because corals vary enormously in size. The great differences in colony size are caused by the coral colony growth process. We studied size distributions in coral species and found that analyzing coral size frequencies using log transformations of colony size has a number of advantages. Coral size distributions become comparable within and between species across space and through time. Such analyses that (1) small colony size and positively skewed size-frequency distributions characterize populations of brooding species.
The most common coral monitoring methods estimate coral abundance as percent cover, either via in situ observations or derived from images. In recent years, growing interest and effort has focused on colony-based (demographic) data to assess the status of coral populations and communities. In this study, we relied on two separate data sets (photo-derived percent cover estimates, 2002–12, and opportunistic in situ demographic sampling, 2004 and 2012) to more fully infer decadal changes in coral communities at a small, uninhabited Caribbean island. Photo-derived percent cover documented drastic declines in coral abundance including disproportionate declines in Orbicella spp. While overall in situ estimates of total coral density were not different between years, densities of several rarer taxa were. Meandrina meandrites and Stephanocoenia intersepta increased while Leptoseris cucullata decreased significantly, changes that were not discernable from the photo-derived cover estimates. Demographic data also showed significant shifts to larger colony sizes (both increased mean colony sizes and increased negative skewness of size frequency distributions, but similar maximum colony sizes) for most taxa likely indicating reduced recruitment. Orbicella spp. differed from this general pattern, significantly shifting to smaller colony sizes due to partial mortality. Both approaches detected significant decadal changes in coral community structure at Navassa, though the demographic sampling provided better resolution of more subtle, taxon-specific changes.
Caribbean journal of Science, 2009
ABSTRACT. — Juvenile coral survivorship (the proportion of juvenile colonies surviving from t 1 to t 2 ) was assessed by counting, photographing and mapping all juveniles found in 2003 within random permanent 0.25m 2 quadrats at four depth intervals at each of four inshore and mid-shelf reefs and at deeper habitats (>18m) in two shelf-edge reefs (N=96/reef) in La Parguera, southwest coast of Puerto Rico. Quadrats were resurveyed and photographed in 2005 to evaluate surviving juveniles, mortality and new recruits. Total number of juveniles dropped from 718 in 31 scleractinian species in 2003 to 396 in 28 species in 2005, an average juvenile survivorship of 54.8%. Mean juvenile density decreased from 1.2 (± 0.06) colonies/0.25 m 2 in 2003 to 0.7 (± 0.05) colonies/0.25 m 2 in 2005. Juvenile coral composition, relative abundances, survivorship and recruitment varied significantly across depth intervals within reefs and among reefs. Some species with high relative abundances in 2003 showed high survivorship in 2005 [ Siderastrea siderea (28.3% and 65% respectively), Porites astreoides (15.1% and 55.6%), and Diploria strigosa (7.5% and 45.2%)]. Other taxa had relative low abundances but high survivorship [ Montastraea cavernosa (4.6% and 66.7%) and Stephanocoenia intersepta (4.6% and 48.3%)]. Survivorship was significantly higher in deeper habitats at three of the four fringing reefs. Furthermore, the semi-exposed inshore, highly sedimented reefs, showed higher juvenile survivorship than the mid-shelf and shelf-edge reefs. There was no clear relationship between survivorship and reproductive mode (brooding vs.broadcast spawning) of sexual reproduction. Overall, only 78 new recruits were found in 2005.
Corals' prolonged struggle against unfavorable conditions
Galaxea, Journal of Coral Reef Studies, 2009
A central goal of coral-reef ecology is to define the key ecological processes that regulate reef populations under a rapidly changing environment. There is considerable need to move away from simply tracking reef state, and move toward more process orientated studies. Differential recruitment, growth, partial mortality, and mortality of corals are fundamental processes that need spatial evaluation using hierarchical sampling. Major changes to any one process will alter the state of the reef. Understanding these key processes, assessing their spatial variation and their relationship with state variables, such as coral cover, will lead to predictive models of population trajectories under different climate change scenarios. Predictions may even guide critical resource allocation to increase coral-reef management efforts at localities that are most likely to persevere in the prolonged struggle against unfavorable conditions.
Ecological Complexity, 2015
Ecological signs of Earth's biosphere forewarn an alarming trajectory towards a global mass-extinction. Assessing species performance and susceptibilities to decline is essential to comprehend and reverse this trend. Yet it is challenging, given difficulties associated with quantifying individual and population processes that are variable across time, space, and life-stages. We describe a new approach to estimating and comparing species performances that combines empirical data, a novel theoretical consideration of population dynamics, and modern statistics. Our approach allows for a more realistic continuous representation of individual performances along development stages while taking into account non-linearity, and natural variability as captured by spatio-temporally replicated observations. We illustrate its application in a coral meta-assemblage composed of populations of the three major reef-building taxa Acropora, Pocillopora, Porites. Using a unique set of highly replicated observations of individual coral dynamics under various environmental conditions, we show how taxa differ in their investment in recruitment and size-specific aptitude for growth and survival, notably through different use of clonal shrinkage, fragmentation, fission, and fusion processes. Our results reveal contrasting life-history trade-offs among taxa which, along with differing patterns of density-dependent recruitment, modulate species responses to decline. These differences in coral life history traits reflect opposing life-strategies, imply regulation at differing lifestages, and explain divergence in species trajectories. Our findings indicate a high potential for resilience in Pocillopora and Porites populations, thanks respectively to a sustained recruitment that promotes demographic elasticity through replacement of individuals, and a steady resistance to mortality which confers persistence through lingering of individuals. Resilience in Acropora appears more arbitrary, given high susceptibility to perturbations and dependency of recruitment on presence of established local populations. We identify management actions that can complement Acropora's life history and benefit recovery of its populations following mortality events. Our regression-modelling approach to quantifying and comparing species performances in different population processes is applicable to all taxa, as illustrated even those with complex clonal life histories, and can be implemented at wide spatio-temporal and taxonomic coverage. It can promote more accurate representation of species dynamics in both descriptive and predictive modelling approaches. The semi-parametric contrast curve method we develop facilitates comparing response variables along continuous explicative metrics while accounting for multiple sources of complexity in empirical data. It should widely benefit investigations in ecology and quantitative science.
Fecundity and the demographic strategies of coral morphologies
Understanding species differences in demographic strategies is a fundamental goal of ecology. In scleractinian corals, colony morphology is tightly linked with many demographic traits, such as size-specific growth and morality. Here we test how well morphology predicts the colony size-fecundity relationship in eight species of broadcast-spawning corals. Variation in colony fecundity is greater among morphologies than between species with a similar morphology, demonstrating that colony morphology can be used as a quantitative proxy for demographic strategies. Additionally, we examine the relationship between size-specific colony fecundity and mechanical vulnerability (i.e., vulnerability to colony dislodgment). Interestingly, the relationship between size-specific fecundity and mechanical vulnerability varied among morphologies. For tabular species, the most fecund colonies are the most mechanically vulnerable, while the opposite is true for massive species. For corymbose and digitate colonies, mechanical vulnerability remains relatively constant as fecundity increases. These results reveal strong differences in the demographic tradeoffs among species of different morphologies. Using colony morphology as a quantitative proxy for demographic strategies can help predict coral community dynamics and responses to anthropogenic change.