Branching archaeocyaths as ecosystem engineers during the Cambrian radiation

The rapid origination and diversification of major animal body plans during the early Cambrian coincide with the rise of Earth's first animal-built framework reefs. Given the importance of scleractinian coral reefs as ecological facilitators in modern oceans, we investigate the impact of archaeocyathan (Class Archaeocyatha) reefs as engineered ecosystems during the Cambrian radiation. In this study, we present the first high-resolution, three-dimensional (3D) reconstructions of branching archaeocyathide (Order Archaeocyathida) individuals from three localities on the Laurentian paleocontinent. Because branched forms in sponges and corals display phenotypic plasticity that preserve the characteristics of the surrounding growth environment, we compare morphological measurements from our fossil specimens to those of modern corals to infer the surface conditions of Earth's first reefs. These data demonstrate that archaeocyaths could withstand and influence the flow of water, accommodate photosymbionts, and build topographically complex and stable structures much like corals today. We also recognize a stepwise increase in the roughness of reef environments in the lower Cambrian, which would have laid a foundation for more abundant and diverse coevolving fauna.     

Reef-building corals act as long-term sink for microplastic

The pollution of the marine environment with microplastics is pervasive. However, microplastic concentrations in the seawater are lower than the number of particles entering the oceans, suggesting that plastic particles accumulate in environmental sinks. Yet, the exact long-term sinks related to the “missing plastic” phenomenon are barely explored. Sediments in nearshore biogenic habitats are known to trap large amounts of microplastics, but also the three-dimensional structures of coral reefs might serve as unique, living long-term sinks. The main framework builders, reef-building corals, have been shown to ingest and overgrow microplastics, potentially leading to a deposition of particles in reef structures. However, little is known about the number of deposited particles and the underlying processes determining the permanent deposition in the coral skeletons. To test whether corals may act as living long-term sink for microplastic, we exposed four reef-building coral species to polyethylene microplastics (200 particles L^?1) in an 18-month laboratory experiment. We found microplastics in all treatment specimens, with low numbers of particles trapped in the coral tissue (up to 2 particles per cm²) and much higher numbers in the skeleton (up to 84 particles per cm³). The numbers of particles accumulated in the coral skeletons were mainly related to coral growth (i.e., skeletal growth in volume), suggesting that deposition is a regularly occurring stochastic process. We estimate that reef-building corals may remove 0.09%–2.82% of the bioavailable microplastics from tropical shallow-reef waters per year. Our study shows for the first time that microplastic particles accumulate permanently in a biological sink, helping to explain the “missing plastic” phenomenon. This highlights the importance of coral reefs for the ecological balance of the oceans and reinforces the need to protect them, not only to mitigate the effects of climate change but also to preserve their ecosystem services as long-term sink for microplastic.     

A precise and non-destructive method to calculate the surface area in living scleractinian corals using X-ray computed tomography and 3D modeling

The surface area of corals represents a major reference parameter for the standardization of flux rates, for coral growth investigations, and for investigations of coral metabolism. The methods currently used to determine the surface area of corals are rather approximate approaches lacking accuracy, or are invasive and often destructive methods that are inapplicable for experiments involving living corals. This study introduces a novel precise and non-destructive technique to quantify surface area in living coral colonies by applying computed tomography (CT) and subsequent 3D reconstruction. Living coral colonies of different taxa were scanned by conventional medical CT either in air or in sea water. Resulting data volumes were processed by 3D modeling software providing realistic 3D coral skeleton surface reconstructions, thus enabling surface area measurements. Comparisons of CT datasets obtained from calibration bodies and coral colonies proved the accuracy of the surface area determination. Surface area quantifications derived from two different surface rendering techniques applied for scanning living coral colonies showed congruent results (mean deviation ranging from 1.32 to 2.03%). The validity of surface area measurement was verified by repeated measurements of the same coral colonies by three test persons. No significant differences between all test persons in all coral genera and in both surface rendering techniques were found (independent sample t-test: all n.s.). Data analysis of a single coral colony required approximately 15 to 30 min for a trained user using the isosurface technique regardless of the complexity and growth form of the latter, rendering the method presented in this study as a time-saving and accurate method to quantify surface areas in both living coral colonies and bare coral skeletons. Communicated by Biology Editor Dr Michael Lesser     

A simple technique for measuring buoyant weight increment of entire, transplanted coral colonies in the field

Estimating the impacts of global and local threats on coral reefs requires monitoring reef health and measuring coral growth and calcification rates at different time scales. This has traditionally been mostly performed in short-term experimental studies in which coral fragments were grown in the laboratory or in the field but measured ex situ. Practical techniques in which growth and measurements are performed over the long term in situ are rare. Apart from photographic approaches, weight increment measurements have also been applied. Past buoyant weight measurements under water involved a complicated and little-used apparatus. We introduce a new method that combines previous field and laboratory techniques to measure the buoyant weight of entire, transplanted corals under water. This method uses an electronic balance fitted into an acrylic glass underwater housing and placed atop of an acrylic glass cube. Within this cube, corals transplanted onto artificial bases can be attached to the balance and weighed at predetermined intervals while they continue growth in the field. We also provide a set of simple equations for the volume and weight determinations required to calculate net growth rates. The new technique is highly accurate: low error of weight determinations due to variation of coral density (< 0.08%) and low standard error (< 0.01%) for repeated measurements of the same corals. We outline a transplantation technique for properly preparing corals for such long-term in situ experiments and measurements.     

Mid-water rope nursery—Testing design and performance of a novel reef restoration instrument

Fast degradation of coral reefs worldwide has promoted the exploitation of active restoration instruments, one of which is the ‘gardening concept’. This concept comprises two phases: (1) establishing in situ coral nurseries for rearing large numbers of coral fragments; (2) their transplantation onto denuded reefs. This study tested the design and performance of a novel mid-water floating nursery instrument, a ‘rope nursery’. This nursery accommodated small coral fragments attached to a rope, creating an easily constructed nursery bed that is rapid and inexpensive. Two sets of experiments were conducted: the first tested two mid-water rope nursery prototypes in small-scale trials that tested depth, coral genotypes and construction stability, whereas the second set incorporated lessons learned from the first set, and was designed to carry larger numbers of colonies. These highly economical nurseries (US$ 0.11/fragment) revealed high survivorship low detachment and fast growth rates compared to previous coral-nursery types. Moreover, the coiling force of the ropes adequately held fragments without adhesives, and the minimal surface area of rope nursery beds provided not only improved water flux around farmed corals, but also reduced proliferation of fouling organisms. The rope nursery prototypes studied here attest to the diversity of their potential uses under various conditions and demands, making the construction of large scale nurseries a very feasible target. This restoration instrument was proven to be an effective coral reef rehabilitation tool.     

Spatial dynamics of benthic competition on coral reefs

The community structure of sedentary organisms is largely controlled by the outcome of direct competition for space. Understanding factors defining competitive outcomes among neighbors is thus critical for predicting large-scale changes, such as transitions to alternate states within coral reefs. Using a spatially explicit model, we explored the importance of variation in two spatial properties in benthic dynamics on coral reefs: (1) patterns of herbivory are spatially distinct between fishes and sea urchins and (2) there is wide variation in the areal extent into which different coral species can expand. We reveal that the size-specific, competitive asymmetry of corals versus fleshy algae highlights the significance of spatial patterning of herbivory and of coral growth. Spatial dynamics that alter the demographic importance of coral recruitment and maturation have profound effects on the emergent structure of the reef benthic community. Spatially constrained herbivory (as by sea urchins) is more effective than spatially unconstrained herbivory (as by many fish) at opening space for the time needed for corals to settle and to recruit to the adult population. Further, spatially unconstrained coral growth (as by many branching coral species) reduces the number of recruitment events needed to fill a habitat with coral relative to more spatially constrained growth (as by many massive species). Our model predicts that widespread mortality of branching corals (e.g., Acropora spp) and herbivorous sea urchins (particularly Diadema antillarum) in the Caribbean has greatly reduced the potential for restoration across the region.     

Importance of live coral habitat for reef fishes

Live corals are the key habitat forming organisms on coral reefs, contributing to both biological and physical structure. Understanding the importance of corals for reef fishes is, however, restricted to a few key families of fishes, whereas it is likely that a vast number of fish species will be adversely affected by the loss of live corals. This study used data from published literature together with independent field based surveys to quantify the range of reef fish species that use live coral habitats. A total of 320 species from 39 families use live coral habitats, accounting for approximately 8 % of all reef fishes. Many of the fishes reported to use live corals are from the families Pomacentridae (68 spp.) and Gobiidae (44 spp.) and most (66 %) are either planktivores or omnivores. 126 species of fish associate with corals as juveniles, although many of these fishes have no apparent affiliation with coral as adults, suggesting an ontogenetic shift in coral reliance. Collectively, reef fishes have been reported to use at least 93 species of coral, mainly from the genus Acropora and Porities and associate predominantly with branching growth forms. Some fish associate with a single coral species, whilst others can be found on more than 20 different species of coral indicating there is considerable variation in habitat specialisation among coral associated fish species. The large number of fishes that rely on coral highlights that habitat degradation and coral loss will have significant consequences for biodiversity and productivity of reef fish assemblages.     

Ecological analyses to inform management targets for the culling of crown-of-thorns starfish to prevent coral decline

The crown-of-thorns starfish (COTS), Acanthaster cf. solaris, is one of the main contributors to declines in coral cover on the Great Barrier Reef (GBR) and remains one of the major acute disturbances on coral reefs throughout much of the Indo-Pacific. Extensive control programs on the GBR involve manual culling of COTS in the field, and research is needed to inform these management efforts. Data from the Great Barrier Reef Marine Park Authority’s (GBRMPA) COTS control program provide near-real-time CPUE (Catch-Per-Unit-Effort, COTS culled per minute) data ideal for operational decision-making but these must be converted to density estimates before they can be related to ecological status of reefs or incorporated into ecological models. We developed conversions between common COTS field survey methods (i.e. manta tow, SCUBA transect searches) and COTS control program CPUE data using estimates of sightability and detectability. We used a population model and COTS size-structure data from COTS control program culling efforts to estimate that, on average, only 19% of 1-yr-old COTS (1–15 cm) are available to be culled. Finally, we developed a CPUE-COTS density relationship to estimate the threshold levels of COTS that prevent net growth of hard corals. Culling programs should therefore aim to achieve CPUEs below these ecological thresholds in order to effectively promote coral growth and recovery. These ecologically sustainable thresholds of COTS density varied depending on hard coral cover. For example, for 35% fast-growing coral cover, COTS culling needs to continue until CPUE decreases to below 0.05 COTS/min (1 COTS per 20 min) in order to prevent coral decline, whereas if coral cover is higher (80%), then a higher target threshold CPUE of ca. 0.08 COTS/min (ca. 3 COTS per 40 min) may be ecologically sustainable. These estimates underpin the current pest management rules being implemented by the GBRMPA in its COTS control program.

     

Modelling the acclimation capacity of coral reefs to a warming ocean

The symbiotic relationship between corals and photosynthetic algae is the foundation of coral reef ecosystems. This relationship breaks down, leading to coral death, when sea temperature exceeds the thermal tolerance of the coral-algae complex. While acclimation via phenotypic plasticity at the organismal level is an important mechanism for corals to cope with global warming, community-based shifts in response to acclimating capacities may give valuable indications about the future of corals at a regional scale. Reliable regional-scale predictions, however, are hampered by uncertainties on the speed with which coral communities will be able to acclimate. Here we present a trait-based, acclimation dynamics model, which we use in combination with observational data, to provide a first, crude estimate of the speed of coral acclimation at the community level and to investigate the effects of different global warming scenarios on three iconic reef ecosystems of the tropics: Great Barrier Reef, South East Asia, and Caribbean. The model predicts that coral acclimation may confer some level of protection by delaying the decline of some reefs such as the Great Barrier Reef. However, the current rates of acclimation will not be sufficient to rescue corals from global warming. Based on our estimates of coral acclimation capacities, the model results suggest substantial declines in coral abundances in all three regions, ranging from 12% to 55%, depending on the region and on the climate change scenario considered. Our results highlight the importance and urgency of precise assessments and quantitative estimates, for example through laboratory experiments, of the natural acclimation capacity of corals and of the speed with which corals may be able to acclimate to global warming.     

大型海藻在珊瑚礁退化过程中的作用

随着全球范围珊瑚礁的退化,大型海藻在珊瑚礁区的覆盖度呈增多的趋势。大型海藻的大量生长,妨碍了珊瑚的生长、繁殖、恢复等过程。概括起来,大型海藻对珊瑚生长、繁殖及恢复过程所产生的不利影响主要包括:(1)大型海藻通过与珊瑚竞争空间和光照而影响珊瑚生长;(2)大型海藻与珊瑚直接接触时,通过摩擦作用及释放化感物质而影响珊瑚生长;(3)大型海藻的大量生长打破了珊瑚与海藻的竞争平衡,珊瑚为应对大型海藻的入侵而把用于生长和繁殖的能量转移到组织修复与防御上,进而造成珊瑚繁殖能量的减少;(4)大型海藻通过影响珊瑚幼虫的附着及附着后的存活率,而阻碍珊瑚群落的发展;(5)海藻还能通过富集沉积物、释放病原体及扰乱珊瑚共生微生物的生长等而间接影响珊瑚生长。明确的竞争机制有利于研究海藻与珊瑚的相互作用过程。在总结前人对海藻与珊瑚的竞争机制研究的基础上,把两者的竞争机制划分成物理机制、化学机制、微生物机制三大类,物理机制是研究得比较透彻的竞争机制,而化学机制与微生物机制则需要更深入的研究,是当前研究的热点。目前,我国对珊瑚礁中底栖海藻与珊瑚的相互作用研究甚少;鉴于此,对底栖海藻功能群的划分类型以及三大类型底栖海藻对珊瑚的作用特点做了简要介绍,并对珊瑚礁退化的现状和退化珊瑚礁区内海藻的表现做了概述。在此基础上,再综述国外关于大型海藻对珊瑚的影响研究进展,指出我国应该加强对南海珊瑚礁区大型海藻的种类分布及丰富度等的调查,评价大型海藻对南海珊瑚礁的影响现状;并结合生理学、分子生物学技术和生态学研究手段,在细胞与分子水平上探索海藻对珊瑚的影响机制,以期为珊瑚礁生态系统的保护提供参考。     

ECOLOGY AND MORPHOLOGY OF RECENT CORAL REEFS

1. The classical ‘coral reef problem’ concerned the geological relationships of reefs as major topographical features; modern coral studies consider reefs both as complex biological systems of high productivity and as geological structures forming a framework for and being modified by coral growth. 2. Deep borings in reefs have conclusively confirmed the general arguments of Darwin, that oceanic reefs developed by progressive subsidence of their foundations. Darwin failed to take account of Pleistocene changes in sea level and their effect on the present surface features of reefs. Daly's alternative ‘glacial control theory’ was based on false assumptions concerning marine erosion rates during glacial periods, but if sea level during the Holocene was higher than at present, as Daly also supposed, the effects on reef features would be profound. 3. Reefs are complex biological systems in tropical seas, dominated by scleractinian corals. Coral faunas are larger and more diverse in the Indo-Pacific than in the Atlantic. Hermatypic corals are restricted to shallow water by the light requirements of their symbiotic algae, but temperature is a major control of worldwide distributions. Temperature, salinity and sediment tolerances of corals are wider than formerly supposed, and corals can survive brief emersion except when it coincides with heavy rainfall. Water turbulence is an important ecological control, but difficult to measure. 4. The trophic status of corals is still unclear, but in spite of their anatomical and physiological specialization as carnivores it is likely that they derive some nutrient substances from zooxanthellae. Suggestions that filamentous algae in coral heads play a major part in the economy of the corals have not been supported by later work, but biomass pyramids constructed on the basis by Odum and Odum remain the only ones available. Most reefs are apparently autotrophic, with 1500–3500 g. Carbon being fixed per m.² per year. 5. Few animals eat corals, which may account for their success. Important predators are fish and the echinoderm Acanthaster. Quantitative estimates of biogenic erosion of organic skeletons on reefs are high. Fish affect not only corals but other invertebrates, algae and marine phanerogams. 6. Corals may be killed by ‘dark water’, intense rain or river floodwaters, earth movements, human interference and especially hurricanes. Reef recovery after hurricanes may take 10–20 years. 7. In addition to fringing, barrier and atoll reefs, intermediate types are recognised. The main types may consist of linear reefs or faros. Smaller lagoon reefs include pinnacles, patches and platforms, and submerged knolls. Complex cellular or mesh reef patterns are also found. 8. Reefs are conspicuously zoned, both laterally in response to changing exposure to waves to form windward and leeward reefs, and transversely, as a result of steep environmental gradients across reef flats from sea to lagoon. Topographic and ecological zones may be characterized by particular coral species, but these vary widely from reef to reef. A major distinction can be made between reefs with and without algal ridges, which are common on open-ocean trade-wind reefs, in the Indo-Pacific, but are absent on Caribbean reefs and on Indo-Pacific reefs in more sheltered waters. gorgonians are common on Caribbean reefs, alcyonaceans in the Indo-Pacific. 9. Much of the difficulty in comparing reefs stems from the lack of uniformity in surveying methods. Problems of describing the complex three-dimensional patterns of organisms on reefs have yet to be solved, and hence little progress has been made in explanation of these patterns. Explanation in terms of simple environmental controls is inadequate. 10. Understanding the distribution of corals is made more difficult both by taxo-nomic problems and by the plasticity of growth form in different situations. 11. Growth of corals and reefs may be estimated by measuring the growth of individual colonies, measuring rates of calcium carbonate deposition in the skeleton, measuring topographic change on the reef and deducing net rates of reef growth from geological evidence. Massive corals may increase in diameter by 1 cm./year, branches of branching corals may increase in length by 10 cm./year. Study of deposition rates shows variation within colonies, between species, in light and dark, and seasonally. Rates of reef growth extrapolated from colony measurements reach 2–5 cm./year, and contrast with figures as low as 0–02 cm/year averaged over 70 million years from borehole data. Both colony growth rates and geological data suggest worldwide variations in rates of reef growth. 12. In spite of clear evidence of long-continued subsidence, present surface features of reefs, often only thinly veneered by modern corals, have been much affected by recent sea level fluctuations. Many slightly raised reefs at 2–10 m. above sea level date at 90–160 thousand years B.P.; there is evidence for a sea level at about the present level at 30–35 thousand years B.P.; and controversy continues over whether sea level has stood higher than the present at any time since the last sea level rise began about 20,000 years ago. Evidence from many reefs suggests a slightly higher sea level in the last 4000 years, but on other reefs such evidence is lacking. 13. Several reef features (submerged terraces, groove-spur systems, algal ridge, reef flat, reef blocks and reef islands) have been interpreted either as relict features dating from a higher sea level in the last 5000 years, or contemporary features developed in response to present processes. In some cases the evidence is equivocal; in others it is clear that diverse features are being grouped together under the same name. If such features are referable to a higher sea level, this may have been of last Interglacial or even Interstadial age rather than Holocene. 14. A reef consists of a rigid framework defining several major depositional environments within and around it. Sediments are of biological, mainly skeletal origin, except in unusual environments such as the Bahama Banks. The characteristics of sediments derived from organisms depend partly on the breakdown patterns of particular skeletons, partly on transportation and sorting processes. Fine sediments may be either detrital, or physicochemical precipitates. 15. Organisms affect sediments after deposition, by disturbance, transportation and probably comminution. Fish and holothurians have been studied in detail. 16. While new theories of coral reefs are proposed from time to time, the need is less for new theories than for standardised procedures to ensure comparability of reef studies and the identification of variations in reefs both on local and regional scales. While reefs as biological systems adjust relatively rapidly to changes, reefs as geological systems adjust much more slowly. Because of the magnitude and recency of Pleistocene fluctuations in sea level, many biological features of reefs are out of phase with inherited geological features, and this had led to much controversy.     

Free-living scleractinian corals on reefs of the Seychelles Islands

Thirty-nine species of unattached scleractinian corals that belong to 22 genera of 9 families were found on the Seychelles reefs. Variations of the colony form of corals living on soft sediments under continuous wave action are described. Irrespective of their initial growth form and taxonomic position, corals assume a form close to spherical. Because of the worldwide deterioration of coral reefs, the adaptation to changing ecological conditions by reef-building corals needs to be studied.     

Mechanical vulnerability explains size‐dependent mortality of reef corals

Understanding life history and demographic variation among species within communities is a central ecological goal. Mortality schedules are especially important in ecosystems where disturbance plays a major role in structuring communities, such as coral reefs. Here, we test whether a trait‐based, mechanistic model of mechanical vulnerability in corals can explain mortality schedules. Specifically, we ask whether species that become increasingly vulnerable to hydrodynamic dislodgment as they grow have bathtub‐shaped mortality curves, whereas species that remain mechanically stable have decreasing mortality rates with size, as predicted by classical life history theory for reef corals. We find that size‐dependent mortality is highly consistent between species with the same growth form and that the shape of size‐dependent mortality for each growth form can be explained by mechanical vulnerability. Our findings highlight the feasibility of predicting assemblage‐scale mortality patterns on coral reefs with trait‐based approaches.     

Newly dominant benthic invertebrates reshape competitive networks on contemporary Caribbean reefs

Competition is a fundamental process structuring ecological communities. On coral reefs, space is a highly contested resource and the outcomes of spatial competition can dictate community composition. In the Caribbean, reefs are increasingly dominated by non-scleractinian species like sponges, gorgonians, and zoanthids, yet there is a paucity of data on interactions between these increasingly common organisms and historically dominant corals. Here, we investigated interactions among these groups of sessile benthic invertebrates to better understand the role of spatial competition in shaping benthic communities on Caribbean reefs. We coupled surveys of competitive interactions on the reef with a common garden competition experiment to determine the frequency and outcome of interference competition among eight focal species. We found that competitive interactions were pervasive on Florida reefs, with 60% of sessile benthic invertebrates interacting with at least one other invertebrate. Increasingly common non-scleractinian species were some of the most abundant taxa and consistently outcompeted the contemporarily common scleractinian species Porites porites and Siderastrea siderea. The encrusting gorgonian, Erythropodium caribaeorum, was the most aggressive species, reducing the live area of its competitors on average 42% ± 7.04 (SE) over the course of 5 months. Surprisingly, the most aggressive species declined in size when competing, while some less aggressive species were able to increase or maintain area, suggesting a trade-off between aggressiveness and growth. Our findings suggest that competition among sessile invertebrates is likely to remain an important process in structuring coral reefs, but that the optimal strategies for maintaining space on the benthos may change. Importantly, many non-scleractinian species that now dominate reefs appear to be superior competitors, potentially increasing the stress on corals on contemporary reefs.

     

Evidence for a host role in thermotolerance divergence between populations of the mustard hill coral (Porites astreoides) from different reef environments

Studying the mechanisms that enable coral populations to inhabit spatially varying thermal environments can help evaluate how they will respond in time to the effects of global climate change and elucidate the evolutionary forces that enable or constrain adaptation. Inshore reefs in the Florida Keys experience higher temperatures than offshore reefs for prolonged periods during the summer. We conducted a common garden experiment with heat stress as our selective agent to test for local thermal adaptation in corals from inshore and offshore reefs. We show that inshore corals are more tolerant of a 6‐week temperature stress than offshore corals. Compared with inshore corals, offshore corals in the 31 °C treatment showed significantly elevated bleaching levels concomitant with a tendency towards reduced growth. In addition, dinoflagellate symbionts (Symbiodinium sp.) of offshore corals exhibited reduced photosynthetic efficiency. We did not detect differences in the frequencies of major (>5%) haplotypes comprising Symbiodinium communities hosted by inshore and offshore corals, nor did we observe frequency shifts (‘shuffling’) in response to thermal stress. Instead, coral host populations showed significant genetic divergence between inshore and offshore reefs, suggesting that in Porites astreoides, the coral host might play a prominent role in holobiont thermotolerance. Our results demonstrate that coral populations inhabiting reefs <10‐km apart can exhibit substantial differences in their physiological response to thermal stress, which could impact their population dynamics under climate change.     

Augmented coral reef monitoring using a stationary reef monitoring system

Coral reef monitoring is a reliable tool to assess the effect of climate change as corals are sensitive to increases in water temperatures between 30 °C and 35 °C resulting in bleaching - a whitening process when the corals lose their color and the reefs begin to die. Existing satellite-based monitoring products facilitate coral bleaching monitoring over large spatial scales, but their use in predicting local scale stress that influences the bleaching severity across reefs is limited. In this paper, we describe a Stationary Reef Monitoring System (SRMS) that monitors the time evolution of coral reefs through the photography of nearby coral clusters. Simultaneously, the SRMS measures and records environmental parameters such as temperature, solar irradiance (PAR), and salinity in the waters surrounding the coral colonies. When deployed in the sea, the SRMS detected a 0.1–0.4 °C variability in temperature between the in situ and satellite datasets. The SRMS uses color photography along with quantitative data on environmental parameters to monitor the health of corals and eliminates the need for physical/visual verification of coral health by a diver. By this approach, one can determine the stress thresholds of corals and identify the vulnerable and resilient reefs so as to prioritize conservation efforts.     

Anthropogenic mortality on coral reefs in Caribbean Panama predates coral disease and bleaching

Caribbean reef corals have declined precipitously since the 1980s due to regional episodes of bleaching, disease and algal overgrowth, but the extent of earlier degradation due to localised historical disturbances such as land clearing and overfishing remains unresolved. We analysed coral and molluscan fossil assemblages from reefs near Bocas del Toro, Panama to construct a timeline of ecological change from the 19th century-present. We report large changes before 1960 in coastal lagoons coincident with extensive deforestation, and after 1960 on offshore reefs. Striking changes include the demise of previously dominant staghorn coral Acropora cervicornis and oyster Dendrostrea frons that lives attached to gorgonians and staghorn corals. Reductions in bivalve size and simplification of gastropod trophic structure further implicate increasing environmental stress on reefs. Our paleoecological data strongly support the hypothesis, from extensive qualitative data, that Caribbean reef degradation predates coral bleaching and disease outbreaks linked to anthropogenic climate change.     

Ecological Physiology of a Coral Pathogen and the Coral Reef Environment

Laboratory studies on the ecological physiology of a coral pathogen were carried out to investigate growth potential in terms of environmental factors that may control coral diseases on reefs. The disease chosen for this study, white plague type II, is considered to be one of the major diseases of Caribbean scleractinian corals, affecting a wide range of coral hosts and causing rapid and widespread tissue loss. It is caused by a single pathogen, the bacterium Aurantimonas coralicida. A series of laboratory experiments using a pure culture of the pathogen was carried out to examine the roles of temperature, pH, and O₂ concentration on growth rate. Results revealed optimal growth between 30 and 35°C, and between pH values of 6 and 8. There was a distinctive synergistic relationship between pH and temperature. Increasing temperature from 25 to 35°C expanded the range of pH tolerance from a minimum of 6.0 down to 5.0. O₂ concentration directly affected growth rate, which increased with increasing O₂. The combined effects of increasing O₂ and increasing temperature resulted in a synergistic effect of more rapid growth. These laboratory results are discussed in terms of the coral host and the range of the environmental factors that occur on coral reefs. We conclude that changing environmental conditions in the reef environment, in particular observed increases in water temperature, may be promoting coral diseases by allowing coral pathogens to expand their ecological niches. In the case of the white plague type II pathogen, elevated temperature would allow A. coralicida to colonize the low pH environment of the coral surface mucopolysaccharide layer as an initial stage of infection. The synergistic effect between temperature and oxygen concentration appeared to be less environmentally relevant for this coral pathogen.     

Long-term heightened larval production in nursery-bred coral transplants

The ‘gardening coral reefs’ method is part of the approaches proposed for counteracting the substantial impacts of global climate change on the survival of coral reefs. It incorporates ecosystem engineering strategies for coral nursery farming and coral colonies out-planting. This study explores the reproductive output of three sets of nursery-grown Stylophora pistillata colonies along eight reproductive seasons following transplantation, as compared to that of native corals. When native and transplanted corals grew side by side in a disturbed environment, the nursery-grown transplants showed enhanced larval release (2.6–22.5 times more planulae/colony; multiyear average: 11.6±1.8 planulae/transplant vs. 1.5±0.3 planulae/native colony) with higher percentages of gravid colonies (91±2.1% transplants vs. 34±7.6% native colonies). The inherently enhanced larval production of transplants, maintained for such a long period of time post-transplantation, reveals a possible enduring impact of the nursery conditions on future fitness and ecological traits of transplants. This is further supported by the emerging documentation regarding the enhanced growth of corals under nursery conditions, which continues to be detected even years after transplantation was conducted on the natural reef. The above enhancement of coral reproduction can be harnessed as a human intervention tool for countering global climate change impacts.     

Growth and population dynamic model of the reef coral Fungia granulosa Klunzinger, 1879 at Eilat, northern Red Sea

The lack of population dynamic information for most species of stony corals is due in part to their complicated life histories that may include fission, fusion and partial mortality of colonies, leading to an uncoupling of coral age and size. However, some reef-building corals may produce compact upright or free-living individuals in which the above processes rarely occur, or are clearly detectable. In some of these corals, individual age may be determined from size, and standard growth and population dynamic models may be applied to gain an accurate picture of their life history. We measured long-term growth rates (up to 2.5 years) of individuals of the free-living mushroom coral Fungia granulosa Klunzinger, 1879 at Eilat, northern Red Sea, and determined the size structure of a population on the shallow reef slope. We then applied growth and population models to the data to obtain estimates of coral age, mortality rate, and life expectancy in members of this species. In the field, few F. granulosa polyps suffered partial mortality of >10% of their tissues. Thus, the majority of polyps grew isometrically and determinately, virtually ceasing growth by about 30-40 years of age. Coral ages as revealed by skeletal growth rings were similar to those estimated from a growth curve based on field data. The frequency of individuals in each age class on the reef slope decreased exponentially with coral age, indicating high mortality rates when corals were young. The maximum coral age observed in the field population (31 years) was similar to that estimated by application of a population dynamic model (30 years). Calculated rates of growth, mortality and life expectancy for F. granulosa were within the range of those known for other stony corals. Our results reveal a young, dynamic population of this species on Eilat reefs, with high turnover rates and short lifespans. Such information is important for understanding recovery of coral reefs from disturbances, and for application to the management of commercially exploited coral populations.