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Tissue loss rather than colony size determines the demographic fate of the branching coral Acropora cervicornis

Authors:
Alex E. Mercado-Molina at University of Puerto Rico at Bayamón
Alex E. Mercado-Molina
Claudia Patricia Ruiz-Diaz at Sociedad Ambiente Marino
Claudia Patricia Ruiz-Diaz
  • Sociedad Ambiente Marino
Alberto M. Sabat at University of Puerto Rico at Río Piedras
Alberto M. Sabat
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Abstract

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
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... The fireworm does not necessarily consume the entire colony; however, it can adversely affect coral demography (Miller et al., 2014). For instance, the survival and growth of A. cervicornis can be compromised if tissue consumption exceeds 20 % of the total colony size (see Mercado-Molina et al., 2018). Moreover, predation can result in population decline if large colonies retrogress into smaller sizes (Mercado-Molina, Ruiz-Diaz, Pérez, et al., 2015). ...
... Predated colonies developed a calcified bulge (or neoplasia, Bak, 1983) at the interface between the live tissue and the exposed skeleton. The bulge, considered a physical barrier for repelling the spread of the algae colonizing dead portions of the colony, is energetically costly and may contribute to the observed decrease in coral growth while increasing survival probability (Bak, 1983;Mercado-Molina et al., 2018). Indeed, no significant difference in survival was observed between predated and non-predated outplants, as none of the affected colonies were consumed entirely or were infected by fireworm-borne diseases (see Miller et al., 2014). ...
... As demonstrated in previous demographic studies on A. cervicornis (Mercado-Molina, Ruiz-Diaz, Pérez, et al., 2015;Mercado-Molina et al., 2020), the stasis of large colonies was the most important transition rate for population growth in PMEL. Large colonies are better able than smaller ones to withstand the negative demographic effects of partial mortality (Hernández-Delgado et al., 2018;Mercado-Molina, Ruiz-Diaz, Pérez, et al., 2015;Mercado-Molina et al., 2018) explaining, in part, the importance of large colonies for population viability. For instance, when a small colony of A. cervicornis loses more than 20 % of its living tissue, its survival is ~ 33 % lower than when a large colony loses the same amount of tissue . ...
Demographic and population response of the threatened coral Acropora cervicornis (Scleractinia, Acroporidae) to fireworm corallivory
Article
Full-text available
  • May 2023
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.
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... variabilis colonies, 37.8 ± 7.0% of P. damicornis and 45.3 ± 13.2% of S. pistillata showed 6.4 ± 2.0%, 9.6 ± 1.0% and 19.3 ± 4.7% partial mortality/ colony, respectively). Considering that partial mortality can potentially affect coral performance 42,43 , especially when transplanted into the challenging environment of Kisuski Beach, we first explored whether the extent of partial mortality at transplantation influenced subsequent colony survival, revealing no significant difference in survival between partially impacted vs. intact colonies at transplantation onset (mixed-model ANOVAs Fig. S4). After the deployment of the RCs, the sandy substrate beneath the trays continuously shifted, passing through the nets (Fig. 1a4-a6), contributed to the occurrence of partial mortality and resulted in a significant increase in the percentage Fig. 1 The construction of Reef Carpets (RCs) on sandy substrates and 17-months follow up of the 3 RCs established. ...
... SCUBA diving surveys were conducted every 2 to 3 months for a total of 17 months starting from the initial RC deployment. During each survey, the following parameters were examined for all transplanted colonies (Table S1c; permits restricted sampling collections): (1) survival; (2) colony selfattachment: assessing the spread of tissue/skeletal growth beyond the initial attachment onto the plastic nail/net; (3) partial colony mortality (bare skeleton areas) caused by sedimentation and predation 42,43 , and/or coral senescence 91 , visually estimated in 5% intervals; (4) fish bites: Identifying lesions caused by the removal of tissue, exposing the underlying skeleton; 59 (5) presence of the gastropod predators Drupella cornus and Coralliophila sp.; (6) disappearance from the RC. Additionally, visual censuses and underwater digital photography were used to document the development of reef-associated communities on the RCs. ...
Shifting reef restoration focus from coral survivorship to biodiversity using Reef Carpets
Article
Full-text available
  • Jan 2024
To enhance the practice of farmed-coral transplantation, we conducted a trial of an approach called “Reef Carpets” (RC), which draws inspiration from the commercial turf-grass sod in land-based lawn gardening. Three 8.4m² RCs were established on a sandy seabed, containing preselected combinations of branching corals (Acropora cf. variabilis, Pocillopora damicornis, Stylophora pistillata) with nursery recruited dwellers, and were monitored for 17-months. Corals within RCs grew, supported coral recruitment and offered ecological habitats for coral-associated organisms. While the unstable sediment underneath the RCs increased corals’ partial mortalities, corals managed to grow and propagate. The extent of fish and gastropods corallivory varied among the coral species and planulation of Stylophora transplants was significantly higher than same-size natal-colonies. The RCs provided conducive environments for fish/invertebrate communities (183 taxa), and each coral species influenced specifically species-diversity and reef-associated communities. Even dead corals played crucial roles as habitats for reef biota, sustaining >80% of the RCs diversity; hence, they should not be considered automatically as indicators of failure. RCs scaled-up reef restoration and generated, in short periods, new reefs in denuded zones with enhanced biodiversity. Yet, RCs employment on soft-beds could be improved by using more structured artificial frameworks, requiring further research efforts.
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... 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). ...
... 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). Accordingly, small colonies' contribution to local population growth tends to be inferior to that of mid-to-large colonies (Mercado-Molina et al., 2015a). ...
Population dynamics of diseased corals: Effects of a Shut Down Reaction outbreak in Puerto Rican Acropora cervicornis
Chapter
  • Oct 2020
  • ADV MAR BIOL
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.
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... Coral shrinkage is rarely reported in coral growth experiments, but current results suggest it may represent an important factor in restoration activities. Coral shrinkage relates to partial mortality and biotic interactions irrespective of coral size as observed during hydrometeorological events (Lirman et al. 2001;Mercado-Molina et al. 2018) or predation (Colgan 1987), but also resulting from coral stress and damage during manipulation (Edwards & Gomez 2007;Tortolero-Langarica et al. 2014;Ng et al. 2017) or related to vulnerability at small coral sizes (Penin et al. 2010;Ishida-Castañeda et al. 2020). As coral shrinkage is not currently reported and small-fragment size co-occurred at the beginning of the experiment, it is complicated to resolve whether shrinkage is related to coral manipulation or size. ...
Gardening Pocillopora spp. fragments and their potential for rebuilding reef systems in the southern Mexican Pacific
Article
Full-text available
  • Sep 2023
  • RESTOR ECOL
The degradation of coral reefs during the last decades has turned attention toward management and restoration interventions. This study seeks to operationalize coral gardening of Pocillopora spp. fragments in low profile bottom-anchored nurseries and to compare survival and growth patterns between sites, time, and fragment size in the southern Mexican Pacific. After 357 days, fragments showed high survival (96.4%), growth rates (4.35 cm/year), and an increase in coral coverage from 3.62 AE 1.3% (mean AE SD) to 17.42 AE 4.8% (approximately 480%). Coral growth rate did not show differences between sites (pseudo-F [1,635] = 0.21, p = 0.63), but corals grew more significantly during the upwelling season in the Gulf of Tehuantepec. According to linear and local regression analysis, the extension rate in nurseries was significantly higher when corals were smaller (<7 cm in diameter) being of relevance for operationalizing coral gardening from donor colonies; nevertheless, coral shrinkage (13.1%), when corals were smaller (i.e. during the early phases of the coral gardening protocol), calls for precaution and close monitoring. Operationalizing coral gardening of Pocillopora spp. fragments, including successful metrics in upwelling areas, are relevant for reef restoration in the eastern tropical Pacific; nevertheless, lessons regarding shrinkage and differential growth rates related to coral size should also be considered.
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... The link between host size and signs of host stress conforms to the understanding of coral life histories. Partial mortality is inherent to the growth of corals (Mercado-Molina et al. 2018), and many drivers of mortality are size-selective (Madin et al. 2014). Thus, large coral colonies are more prone to partial mortality than small coral colonies, and small colonies are more likely to die than are large colonies (Hughes & Jackson 1985, Babcock 1991, Vardi et al. 2012). ...
Twenty-year record of white pox disease in the Florida Keys: importance of environmental risk factors as drivers of coral health
Article
Full-text available
  • Jun 2023
Declining coral populations worldwide place a special premium on identifying risks and drivers that precipitate these declines. Understanding the relationship between disease outbreaks and their drivers can help to anticipate when the risk of a disease pandemic is high. Populations of the iconic branching Caribbean elkhorn coral Acropora palmata have collapsed in recent decades, in part due to white pox disease (WPX). To assess the role that biotic and abiotic factors play in modulating coral disease, we present a predictive model for WPX in A. palmata using 20 yr of disease surveys from the Florida Keys plus environmental information collected simultaneously in situ and via satellite. We found that colony size was the most influential predictor for WPX occurrence, with larger colonies being at higher risk. Water quality parameters of dissolved oxygen saturation, total organic carbon, dissolved inorganic nitrogen, and salinity were implicated in WPX likelihood. Both low and high wind speeds were identified as important environmental drivers of WPX. While high temperature has been identified as an important cause of coral mortality in both bleaching and disease scenarios, our model indicates that the relative influence of HotSpot (positive summertime temperature anomaly) was low and actually inversely related to WPX risk. The predictive model developed here can contribute to enabling targeted strategic management actions and disease surveillance, enabling managers to treat the disease or mitigate disease drivers, thereby suppressing the disease and supporting the persistence of corals in an era of myriad threats.
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... Decreasing coral condition over time is important because it has negative implications for population growth. For example, in Puerto Rico, the growth and survival of A. cervicornis colonies declined significantly when partial mortality exceeded 20% [95]. Most colonies outplanted in the projects reported here exceeded this threshold at three years and exceeded 50% by four years. ...
Survivorship and growth in staghorn coral (Acropora cervicornis) outplanting projects in the Florida Keys National Marine Sanctuary
Article
Full-text available
Significant population declines in Acropora cervicornis and A. palmata began in the 1970s and now exceed over 90%. The losses were caused by a combination of coral disease and bleaching, with possible contributions from other stressors, including pollution and predation. Reproduction in the wild by fragment regeneration and sexual recruitment is inadequate to offset population declines. Starting in 2007, the Coral Restoration Foundation™ evaluated the feasibility of outplanting A. cervicornis colonies to reefs in the Florida Keys to restore populations at sites where the species was previously abundant. Reported here are the results of 20 coral outplanting projects with each project defined as a cohort of colonies outplanted at the same time and location. Photogrammetric analysis and in situ monitoring (2007 to 2015) measured survivorship, growth, and condition of 2419 colonies. Survivorship was initially high but generally decreased after two years. Survivorship among projects based on colony counts ranged from 4% to 89% for seven cohorts monitored at least five years. Weibull survival models were used to estimate survivorship beyond the duration of the projects and ranged from approximately 0% to over 35% after five years and 0% to 10% after seven years. Growth rate averaged 10 cm/year during the first two years then plateaued in subsequent years. After four years, approximately one-third of surviving colonies were ≥ 50 cm in maximum diameter. Projects used three to sixteen different genotypes and significant differences did not occur in survivorship, condition, or growth. Restoration times for three reefs were calculated based on NOAA Recovery Plan (NRP) metrics (colony abundance and size) and the findings from projects reported here. Results support NRP conclusions that reducing stressors is required before significant population growth and recovery will occur. Until then, outplanting protects against local extinction and helps to maintain genetic diversity in the wild.
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Outplanting technique, host genotype, and site affect the initial success of outplanted Acropora cervicornis
Article
Full-text available
  • Feb 2018
Acropora cervicornis is the most widely used coral species for reef restoration in the greater Caribbean. However, outplanting methodologies (e.g., colony density, size, host genotype, and attachment technique) vary greatly, and to date have not been evaluated for optimality across multiple sites. Two experiments were completed during this study, the first evaluated the effects of attachment technique, colony size, and genotype by outplanting 405A. cervicorniscolonies, from ten genotypes, four size classes, and three attachment techniques (epoxy, nail and cable tie, or puck) across three sites. Colony survival, health condition, tissue productivity, and growth were assessed across one year for this experiment. The second experiment assessed the effect of colony density by outplanting colonies in plots of one, four, or 25 corals per 4 m2across four separate sites. Plot survival and condition were evaluated across two years for this experiment in order to better capture the effect of increasing cover. Colonies attached with a nail and cable tie resulted in the highest survival regardless of colony size. Small corals had the lowest survival, but the greatest productivity. The majority of colony loss was attributed to missing colonies and was highest for pucks and small epoxied colonies. Disease and predation were observed at all sites, but did not affect all genotypes, however due to the overall low prevalence of either condition there were no significant differences found in any comparison. Low density plots had significantly higher survival and significantly lower prevalence of disease, predation, and missing colonies than high density plots. These results indicate that to increase initial outplant success, colonies of many genotypes should be outplanted to multiple sites using a nail and cable tie, in low densities, and with colonies over 15 cm total linear extension.
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Porites superfusa mortality and recovery from a bleaching event at Palmyra Atoll, USA
Article
Full-text available
  • May 2017
Background The demography of a coral colony is not a binary trajectory of life and death. Based on the flexibility afforded by colonial organization, most reef-building corals employ a variety of dynamic survival strategies, including growth and shrinkage. The demographic flexibility affects coral size, shape and reproductive output, among other factors. It is thus critical to quantify the relative importance of key dynamics of recruitment, mortality, growth and shrinkage in changing the overall cover of coral on a reef. Methods Using fixed photographic quadrats, we tracked the patterns of change in the cover of one common central Pacific coral, Porites superfusa, before and after the 2009 ENSO event. Results Coral colonies suffered both whole and partial colony mortality, although larger colonies were more likely to survive. In subsequent years, recruitment of new colonies and regrowth of surviving colonies both contributed to the modest recovery of P. superfusa. Discussion This study is unique in its quantitative comparisons of coral recruitment versus regrowth during periods of areal expansion. Our data suggest that recovery is not limited simply to the long pathway of settlement, recruitment and early growth of new colonies but is accelerated by means of regrowth of already established colonies having suffered partial mortality.
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Recurrent partial mortality events in winter shape the dynamics of the zooxanthellate coral Oculina patagonica at high latitude in the Mediterranean
Article
Full-text available
  • Oct 2016
Global warming has many biological effects on corals and plays a central role in the regression of tropical coral reefs; therefore, there is an urgent need to understand how some coral species have adapted to environmental conditions at higher latitudes. We examined the effects of temperature and light on the growth of the zooxanthellate coral Oculina patagonica (Scleractinia, Oculinidae) at the northern limit of its distribution in the eastern Iberian Peninsula (western Mediterranean) by transplanting colonies onto plates and excluding them from space competition over a ~4-yr period. Each year, most of the colonies (~70%) exhibited denuded skeletons with isolated polyps persisting on approximately half of the coral surface area. These recurrent episodes of partial coral mortality occurred in winter, and their severity appeared to be related to colony exposure to cold but not to light. Although O. patagonica exhibited high resistance to stress, coral linear extension did not resume until the coenosarc regenerated. The resumption of linear extension was related to the dissociation of the polyps from the coenosarc and the outstanding regenerative capacity of this species (10.3 mm² d⁻¹). These biological characteristics allow the species to survive at high latitudes. However, the recurrent and severe pattern of denuded skeletons greatly affects the dynamics of the species and may constrain population growth at high latitudes in the Mediterranean.
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Scraping and extirpating: Two strategies to induce recovery of diseased Gorgonia ventalina sea fans
Article
Full-text available
  • Feb 2016
  • MAR ECOL-EVOL PERSP
Coral diseases are currently playing a major role in the worldwide decline in coral reef integrity. One of the coral species most afflicted by disease in the Caribbean, and which has been the focus of much research, is the sea fan Gorgonia ventalina. There is, however, very little information regarding the capacity of sea fans to recover after being infected. The aim of this study was to compare the rehabilitation capacity of G. ventalina after diseased-induced lesions were eliminated either by scraping or extirpating the affected area. Scraping consisted of removing any organisms overgrowing the axial skeleton from the diseased area as well as the purple tissue bordering these overgrowths using metal bristle brushes. Extirpation consisted of cutting the diseased area, including the surrounding purpled tissue, using scissors. The number of scraped colonies that fully or partially rehabilitated after being manipulated and the rates at which the sea fans whose lesions were scrapped grew back healthy tissue were compared among: (i) colonies that inhabited two sites with contrasting environmental conditions; (ii) colonies of different sizes and (iii) colonies with different ratios of area of legions to total colony area (LA/CA). Both strategies proved to be very successful in eliminating lesions from sea fans. In the case of scraping, over 51% of the colonies recovered between 80% and 100% of the lost tissue within 16 months. The number of colonies that recovered from scraping was similar among sites and among colony sizes, but differed significantly depending on the relative amount of lesion to colony area (LA/CA). When lesions were extirpated, lesions did not reappear in any of the colonies. We conclude that lesion scraping is useful for eliminating relatively small lesions (i.e. LA/CA < 10%), as these are likely to recover in a shorter period of time, whereas for relatively large lesions (LA/CA ≥ 10%) it is more appropriate to extirpate the lesion.
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Essential Statistical Concepts for the Quality Professional
Book
  • May 2012
The essence of any root cause analysis in our modern quality thinking is to go beyond the actual problem. This means not only do we have to fix the problem at hand but we also have to identify why the failure occurred and what was the opportunity to apply the appropriate knowledge to avoid the problem in the future. Essential Statistical Concepts for the Quality Professional offers a new non-technical statistical approach to quality for effective improvement and productivity by focusing on very specific and fundamental methodologies and tools for the future. Written by an expert with more than 30 years of experience in management, quality training, and consulting, the book examines the fundamentals of statistical understanding, and by doing so demonstrates the importance of using statistics in the decision making process. The author points out pitfalls to keep in mind when undertaking an experiment for improvement and explains how to use statistics in improvement endeavors. He discusses data interpretation, common tests and confidence intervals, and how to plan experiments for improvement. The book expands the notion of experimentation by dealing with mathematical models such as regression to optimize the improvement and understand the relationship between several factors. It emphasizes the need for sampling and introduces specific techniques to make sure accuracy and precision of the data is appropriate and applicable for the study at hand. The author's approach is somewhat new and unique; however, he details tools and methodologies that can be used to evaluate the system for prevention. These tools and methodologies focus on structured, repeatable processes that can be instrumental in finding real, fixable causes of the human errors and equipment failures that lead to quality issues.
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Effects of predation and nutrient enrichment on the success and microbiome of a foundational coral
Article
  • Mar 2017
By inflicting damage to prey tissues, consumer species may increase stress in prey hosts and reduce overall fitness (i.e., primary effects, such as growth or reproduction) or cause secondary effects by affecting prey interactions with other species such as microbes. However, little is known about how abiotic conditions affect the outcomes of these biotic interactions. In coral reef communities, both nutrient enrichment and predation have been linked to reduced fitness and disease facilitation in corals, yet no study to date has tested their combined effects on corals or their associated microbial communities (i.e., microbiomes). Here, we assess the effects of grazing by a prevalent coral predator (the short coral snail, Coralliophila abbreviata) and nutrient enrichment on staghorn coral, Acropora cervicornis, and its microbiomes using a factorial experiment and high-throughput DNA sequencing. We found that predation, but not nutrients, significantly reduced coral growth and increased mortality, tissue loss, and turf algae colonization. Partial predation and nutrient enrichment both independently altered coral microbiomes such that one bacterial genus came to dominate the microbial community. Nutrient-enriched corals were associated with significant increases in Rickettsia-like organisms, which are currently one of several microbial groups being investigated as a disease agent in this coral species. However, we found no effects of nutrient enrichment on coral health, disease, or their predators. This research suggests that in the several months following coral transplantation (i.e., restoration) or disturbance (i.e., recovery), Caribbean acroporid corals appear to be highly susceptible to negative effects caused by predators, but not or not yet susceptible to nutrient enrichment despite changes to their microbial communities.
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Branching dynamics of transplanted colonies of the threatened coral Acropora cervicornis: Morphogenesis, complexity, and modeling
Article
  • Sep 2016
  • J EXP MAR BIOL ECOL
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.
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Temporal consistency in background mortality of four dominant coral taxa along Australia’s Great Barrier Reef
Article
  • Apr 2016
Studies on the population and community dynamics of scleractinian corals typically focus on catastrophic mortality associated with acute disturbances (e.g., coral bleaching and outbreaks of crown-of-thorns starfish), though corals are subject to high levels of background mortality and injuries caused by routine and chronic processes. This study quantified prevalence (proportion of colonies with injuries) and severity (areal extent of injuries on individual colonies) of background mortality and injuries for four common coral taxa (massive Porites, encrusting Montipora, Acropora hyacinthus and branching Pocillopora) on the Great Barrier Reef, Australia. Sampling was conducted over three consecutive years during which there were no major acute disturbances. A total of 2276 adult colonies were surveyed across 27 sites, within nine reefs and three distinct latitudinal sectors. The prevalence of injuries was very high (>83%) across all four taxa, but highest for Porites (91%) and Montipora (85%). For these taxa (Montipora and Pocillopora), there was also significant temporal and spatial variation in prevalence of partial mortality. The severity of injuries ranged from 3% to more than 80% and varied among coral taxa, but was fairly constant spatially and temporally. This shows that some injuries have considerable longevity and that corals may invest relatively little in regenerating tissue over sites of previous injuries. Inter-colony variation in the severity of injury also had no apparent effect on the realized growth of individual colonies, suggesting that energy diverted to regeneration has a limited bearing on overall energetic allocation, or impacts on other life-history processes (e.g., reproduction) rather than growth. Establishing background levels of injury and regeneration is important for understanding energy investment and life-history consequences for reef-building corals as well as for predicting susceptibility to, and capacity to recover from, acute disturbances.
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