Coral Growth Research Articles

Corallivory on small Porites colonies increases with coral colony size but is reduced by macroalgal associational refuge

Numerous tropical macroalgae provide associational refuge to other benthic organisms, presumably due to their physical structure and/or production of chemical metabolites. One feature determining their effectiveness as an associational refuge is likely to be the size of the organism benefitting from the refuge. Using a manipulative experiment in the back reef of Moorea, French Polynesia, we tested if the macroalga Turbinaria ornata provided an associational refuge from fish corallivores for small colonies of massive Porites spp., and how this differed with colony size (20–100 mm diameter). Tissue loss through corallivory increased with colony size but was ~ 72% less for Porites colonies associated with T. ornata versus colonies separated from this macroalga, while dense macroalgae beds on contemporary reefs negatively impact the recruitment, growth and survival of corals, small colonies of Porites appear to benefit, through reduced corallivory, by associating with the macroalga Turbinaria. This association may come at a cost (e.g., reduced growth) and should be the focus of future research.

Enhancing subsea asset performance: Investigating the biomimetic functionality of the Mushroom Reef design in hydrodynamics, stability, and sedimentation

In this study, laboratory and in situ experiments were performed to assess the stability of the Mushroom Forest Artificial Reef (MFAR) against the hydrodynamic forces of waves and currents and its functionality to avoid sedimentation. Physical modelling was performed in wave flume (waves only) and a long channel (currents only) with a smooth flat bed and a sediment bed. The results illustrated the positive and negative aspects, and then some modifications were made to the in situ experiments. A total of 130 prototype units were produced and deployed at an offshore site in the Arabian Gulf. Sediment traps were installed at the top and base of the mushroom units, and underwater visual assessments were performed to evaluate the stability and sediment behaviour around the studied reefs. The results demonstrated the stability of the units under hydrodynamic loading, with meagre resistance to current displacement (drag forces), with high stability (95% remained vertical), with horizontal vortices leading the sedimentation patterns, and with 46 times less sedimentation at the top than at the base. Thus encouraging coral growth at the mushroom's top with fewer sedimentation risks. In conclusion, MFAR was validated as a blue engineering technology despite some limitations.

Thermotolerant coral-algal mutualisms maintain high rates of nutrient transfer while exposed to heat stress.

Symbiotic mutualisms are essential to ecosystems and numerous species across the tree of life. For reef-building corals, the benefits of their association with endosymbiotic dinoflagellates differ within and across taxa, and nutrient exchange between these partners is influenced by environmental conditions. Furthermore, it is widely assumed that corals associated with symbionts in the genus Durusdinium tolerate high thermal stress at the expense of lower nutrient exchange to support coral growth. We traced both inorganic carbon (H13CO3-) and nitrate (15NO3-) uptake by divergent symbiont species and quantified nutrient transfer to the host coral under normal temperatures as well as in colonies exposed to high thermal stress. Colonies representative of diverse coral taxa associated with Durusdinium trenchii or Cladocopium spp. exhibited similar nutrient exchange under ambient conditions. By contrast, heat-exposed colonies with D. trenchii experienced less physiological stress than conspecifics with Cladocopium spp. while high carbon assimilation and nutrient transfer to the host was maintained. This discovery differs from the prevailing notion that these mutualisms inevitably suffer trade-offs in physiological performance. These findings emphasize that many host-symbiont combinations adapted to high-temperature equatorial environments are high-functioning mutualisms; and why their increased prevalence is likely to be important to the future productivity and stability of coral reef ecosystems.

Gardening Pocillopora spp. fragments and their potential for rebuilding reef systems in the southern Mexican Pacific

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 ± 1.3% (mean ± SD) to 17.42 ± 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.

Developmental history of a newly discovered chain of paired mound and depression structures on the southwestern continental shelf of the Ulleung Basin, East Sea, Korea

A chain of paired mound and depression structures are presented in the southwestern continental shelf of the Ulleung Basin, East Sea, Korea. We integrate multibeam bathymetry to identify topographic features, sub-bottom profile and multi-channel seismic reflection data to confirm geological features, and piston cores to understand the sediments of the mounds and depressions. Paired structures occur with a northwest–southeast orientation at water depths between 130 and 150 m and have similar scales of 10–20 m in height and depth. The mounds consist of cold-water corals and authigenic carbonate with shelly sand, whereas, the surficial lithology of depressions are only composed of siliciclastic deposits. The mounds appeared to have grown from the depression based on the observation for morphological features in the cross-section profiles of the paired mound and depression structures. Seismic profiles show acoustic blanking anomalies and seismic chimneys, indicating that the topographic relief formed under the influence of gas seepage. The petrological and geochemical signature of carbonate chunks also displayed gas leak effects different from CWC. This study suggests a developmental history model with paired mound and depression structures, in which gas/fluid escape causes depressions and the selective coral growth creates mounds growing on one side of these depressions. The mounds had sufficiently grown, depressions would have been further developed in interaction with the bottom current.

Assessing the remaining carbon budget through the lens of policy-driven acidification and temperature targets

Basing a remaining carbon budget on warming targets is subject to uncertainty due to uncertainty in the relationship between carbon emissions and warming. Framing emissions targets using a warming target therefore may not prevent dangerous change throughout the entire Earth system. Here, we use a climate emulator to constrain a remaining carbon budget that is more representative of the entire Earth system by using a combination of both warming and ocean acidification targets. The warming targets considered are the Paris Agreement targets of 1.5 and 2 °C; the acidification targets are −0.17 and −0.21 pH units, informed by aragonite saturation states where coral growth begins to be compromised. The aim of the dual targets is to prevent not only damage associated with warming, but damage to corals associated with atmospheric carbon and ocean acidification. We find that considering acidification targets in conjunction with warming targets narrows the uncertainty in the remaining carbon budget, especially in situations where the acidification target is more stringent than, or of similar stringency to, the warming target. Considering a strict combination of the two more stringent targets (both targets of 1.5 °C warming and −0.17 acidification must be met), the carbon budget ranges from −74.0 to 129.8PgC. This reduces uncertainty in the carbon budget from by 29% (from 286.2PgC to 203.8PgC). This reduction comes from reducing the high-end estimate of the remaining carbon budget derived from just a warming target. Assuming an emissions rate held constant since 2021 (which is a conservative assumption), the budget towards both targets was either spent by 2019 or will be spent by 2026.Plain language summaryThe relationship between atmospheric CO2 and warming is uncertain, which means that we do not know precisely how much carbon we have left to emit until we reach the Paris Agreement warming targets of 1.5 and 2 °C. However, the relationship between atmospheric CO2 and ocean acidification is better understood, so by considering targets for acidification rather than warming alone, we can narrow down our estimate of how much emitted carbon is acceptable. Including acidification targets as well as warming targets means that we can directly address the issue of ocean acidification, which poses a threat to corals and the ecosystems reliant on them. By considering acidification and warming targets together, we can lower uncertainty in acceptable carbon emissions by 29%.

Growth Rate of Coral Transplantation of Acropora formosa in Tidung Island, Kepulauan Seribu Regency, Province of DKI Jakarta

Coral reefs are typical tropical ecosystems that have an important role but are vulnerable to damage. Corals need a long time to recover. One effort to accelerate the growth rate of coral reefs is coral transplantation. This research was conducted from June to July 2022. The research location was on Tidung Island, Thousand Islands Regency, DKI Jakarta. The results showed that the physico-chemical conditions of the waters in general were still within the range of quality standards for marine biota, especially for coral reef ecosystems. the recorded survival percentage was 100%. The growth of coral types tends to increase with height gains ranging from 27-40 cm/week. Coral growth rate ranged from 0,01-0,02 cm/week. Overall the coral transplantation of A. Formosa carried out on Tidung Island can be said to be successful because the water conditions on Tidung Island are suitable for supporting coral transplantation activities.

Exploring New Frontiers in Coral Nurseries: Leveraging 3D Printing Technology to Benefit Coral Growth and Survival

Coral nurseries and associated techniques are the most common and widespread reef restoration methods worldwide. Due to the rapid decline of coral reefs, coral nurseries need to be eco-friendlier and adapted for effective upscaling to support large restoration projects. We suggest new design and fabrication processes associated with coral gardening and transplantation with 3D printing technology to offer a beneficial solution for growing coral fragments in on-land and underwater nurseries. We describe multiple combinations of building nurseries through the integration of biomimetic substrates and novel solutions for attaching coral fragments. Our methods are supported with supplemental testing of two hybrid substrate designs and coral mounting structures, building upon previous studies in the Gulf of Eilat/Aqaba (GoE/A), Red Sea. We identified and quantified marine invertebrates colonizing the surfaces of our substrates with environmental DNA (eDNA) by targeting the mitochondrial COI gene. We evaluated our coral fragments with and without our mounting structures to obtain an indication of total protein as a proxy for tissue health. We demonstrate the ability to design hybrid nurseries with custom mounting structures using biomimetic substrates, such as large ceramic artificial reefs, or with an interlocking mesh for holding numerous fragments to maximize out-planting efforts. We propose several methods for both land and underwater nurseries catered to various restoration initiatives for cost-effective up-scaling to meet the demands of global reef restoration.

Branching coral growth and visual health during bleaching and recovery on the central Great Barrier Reef

Coral reefs are under threat from cumulative impacts such as cyclones, crown-of-thorns starfish (COTS) outbreaks and climate-driven coral bleaching events. Branching corals are more severely impacted by these events than other coral morphologies due to their sensitivity to heat stress and weaker skeletons and COTS preferred prey. The central Great Barrier Reef experienced unprecedented back-to-back bleaching events in 2016 and 2017. This study commenced in 2017 at the peak of heat stress and examined the impact of the heatwave on the survival and recovery of corals by assessing the growth, health (based on the visual health index) and physiological parameters (chlorophyll a, zooxanthellae density, lipid and protein content) of two species, Acropora millepora and Pocillopora acuta (N = 60 colonies for each species). It was conducted across a gradient of turbidity at three reefs, Pandora, Orpheus and Rib, that experienced in April 2017, degree heating weeks (DHW) of 9, 8 and 7, respectively. Orpheus experienced the worst bleaching, based on visual health score, followed by Rib and Pandora. Rib experienced the greatest mortality (78% by Nov 2017); however, this was attributed to the presence of actively feeding crown-of-thorns starfish. Growth rates of A. millepora were almost twice the rate of P. acuta. Both species showed significant seasonal variation with growth of A. millepora and P. acuta 35–40% and 23–33% significantly greater in the summer, respectively. Differences in growth rates were best explained by indicators of energy acquisition. For example, the most important predictor variable in determining higher growth rates and visual health score in A. millepora was chlorophyll a content. For P. acuta, visual health score was the best predictor variable for higher growth rates. This study highlights the important role that chlorophyll a and associated symbionts play in growth and survival in these corals during and after a heat stress event.

Reef-building corals farm and feed on their photosynthetic symbionts

Coral reefs are highly diverse ecosystems that thrive in nutrient-poor waters, a phenomenon frequently referred to as the Darwin paradox1. The energy demand of coral animal hosts can often be fully met by the excess production of carbon-rich photosynthates by their algal symbionts2,3. However, the understanding of mechanisms that enable corals to acquire the vital nutrients nitrogen and phosphorus from their symbionts is incomplete4–9. Here we show, through a series of long-term experiments, that the uptake of dissolved inorganic nitrogen and phosphorus by the symbionts alone is sufficient to sustain rapid coral growth. Next, considering the nitrogen and phosphorus budgets of host and symbionts, we identify that these nutrients are gathered through symbiont ‘farming’ and are translocated to the host by digestion of excess symbiont cells. Finally, we use a large-scale natural experiment in which seabirds fertilize some reefs but not others, to show that the efficient utilization of dissolved inorganic nutrients by symbiotic corals established in our laboratory experiments has the potential to enhance coral growth in the wild at the ecosystem level. Feeding on symbionts enables coral animals to tap into an important nutrient pool and helps to explain the evolutionary and ecological success of symbiotic corals in nutrient-limited waters.

Symbiotic communities associated with nursery-reared and natural corals: are they similar?

Coral aquaculture techniques have been developed for many species based on a well-documented understanding of the factors that affect coral growth and fitness. However, there is limited knowledge about the composition and structure of ectosymbiotic communities associated with cultured coral colonies. To address this gap, we conducted a study ofPocillopora verrucosacolonies reared from fragments in fixed nurseries and exposed for 6 and 12 months, as well as natural colonies in the same location. Our analysis focused on the species composition, species richness, and density of obligate and facultative ectosymbionts associated with the colonies. Obtained results indicate that the community associated with nursery-reared colonies was highly diverse, comprising 25 ectosymbionts, including 9 obligate and 16 facultative species. The prevalence, species richness, and density of the communities associated with natural colonies were significantly higher than those associated with reared ones. We also observed differences in the communities associated with reared colonies of different exposures, but we were able to group them as stages of the same community based on the size and exposure of the colonies. The differences between communities associated with reared and natural colonies may be related to the microhabitat properties of the symbiotic communities, as the former were elevated above the substrate, while the latter were attached to it. The age of natural colonies was also estimated to be more than three times higher than that of reared colonies of the same size, contributing to the differences. Our study clearly demonstrates that coral nurseries not only serve as a means of propagating corals but also offer artificial habitats for the maintenance and conservation of associated fauna. These findings have important implications for the management and conservation of coral reefs.

Tank fouling community enhances coral microfragment growth.

Anthropogenic stressors threaten reefs worldwide and natural in situ coral reproduction may be inadequate to meet this challenge. Land-based culture can provide increased coral growth, especially with microfragments. We tested whether culture methods using different algal fouling communities could improve the growth and health metrics of microfragments of the Hawaiian coral, Porites compressa. Culture method fouling communities were: (1) similar to a reef environment (Mini Reef); (2) clean tanks managed to promote crustose coralline algae (Clean Start); and (3) tanks curated beforehand with poorly-competing algae (Green Film) assessed in winter and summer months. The Green Film method during the winter produced the fastest microfragment mean growth at 28 days until the first row of new polyps developed, and also the highest tank and plate metric health scores. Time efficient, standardized methods for land-based culture designed to maximize growth and production of coral fragments will contribute considerably to the success of large-scale restoration efforts.

Ontogenetic differences in the response of the cold-water coral Caryophyllia huinayensis to ocean acidification, warming and food availability

Cold-water corals (CWCs) are considered vulnerable to environmental changes. However, previous studies have focused on adult CWCs and mainly investigated the short-term effects of single stressors. So far, the effects of environmental changes on different CWC life stages are unknown, both for single and multiple stressors and over long time periods. Therefore, we conducted a six-month aquarium experiment with three life stages of Caryophyllia huinayensis to study their physiological response (survival, somatic growth, calcification and respiration) to the interactive effects of aragonite saturation (0.8 and 2.5), temperature (11 and 15 °C) and food availability (8 and 87 μg C L−1). The response clearly differed between life stages and measured traits. Elevated temperature and reduced feeding had the greatest effects, pushing the corals to their physiological limits. Highest mortality was observed in adult corals, while calcification rates decreased the most in juveniles. We observed a three-month delay in response, presumably because energy reserves declined, suggesting that short-term experiments overestimate coral resilience. Elevated summer temperatures and reduced food supply are likely to have the greatest impact on live CWCs in the future, leading to reduced coral growth and population shifts due to delayed juvenile maturation and high adult mortality.

An Integrated Micro-Device System for Coral Growth and Monitoring.

Corals are fundamental organisms in marine and coastal ecosystems. With the advancement of coral protection research in recent years, precise control of the coral culture environment is highly in demand for coral conservation and study. Here, we developed a semi-closed coral culture micro-device system as a multi-functional platform, which can provide accurate and programmable temperature control, a sterile initial environment, long-term stable water quality, an adjustable dissolved oxygen concentration, and a customized light spectrum for corals. Owing to the modular design, the coral culture system can be upgraded or modified by installing desirable new modules or removing existing ones. Currently, under appropriate conditions and with proper system maintenance, the sample corals can survive for at least 30 days in a healthy state. Furthermore, due to the controllable and sterile initial environment, this coral culture system can support research into the symbiotic relationship between corals and associated microorganisms. Therefore, this micro-device system can be applied to monitor and investigate sea corals in a relatively quantitative manner.

Heterotrophy, microbiome, and location effects on restoration efficacy of the threatened coral Acropora palmata

The iconic and threatened Caribbean coral, Acropora palmata, is an essential reef-ecosystem engineer. Understanding the processes underpinning this coral’s survival and growth is essential to restoring this foundational species. Here, we compared replicate A. palmata colonies transplanted along 350 km of Florida’s offshore coral reef to determine holobiont and/or environmental variables that predict transplant success. We found a west-to-east gradient in coral physiology coupled with site-specific coral-associated microbiomes. Interestingly, no variables were linked to coral genet. Our results suggest that the unique oceanographic conditions with periodic upwelling events in the Dry Tortugas provide corals with greater opportunity for heterotrophy that in turn enhances coral growth and survivorship, and positively influences the microbiome. Our findings indicate that restoration efforts in the Dry Tortugas, and other places exhibiting higher food availability, could be most effective for A. palmata.

Biomass of key grazing fishes is an important determinant of coral growth and fouling control in coral nurseries

Restoration is an emerging tool for coral reef conservation, yet despite small‐scale successes there are concerns about high costs and ecological setbacks. Integration between reef ecology and restoration could help address such concerns. A prime example is the use of grazing by herbivores to reduce coral nursery cleaning costs. However, the relation between herbivore communities and cleaning benefits remains unquantified. This study aimed to measure links between herbivorous fish communities, grazing intensity and coral nursery performance. Six reefs were selected in southern Kenya, equally divided across three levels of fisheries management (fished < reserve < no‐take). Fish surveys determined herbivorous fish biomass and composition, and remote underwater videos recorded grazing intensity on coral nurseries. Accumulated fouling and coral growth were measured at the end of the 4‐month study. Grazing intensity was sixfold lower and fouling density fourfold higher in the fished areas compared to protected zones. Higher fouling strongly correlated with lower coral growth: exponential growth constants in fished areas were respectively twice and three times as low compared to marine reserves and no‐take zones. Across study sites grazing was dominated by bristletooth tangs (Ctenochaetus spp.), except where these were outcompeted by territorial damselfish. Thus, better coral nursery performance in protected areas can be partially linked to higher grazing intensity, which in turn is determined by both fish biomass and local species composition. We recommend protecting herbivorous fish species and placing coral nurseries in areas with high biomass of key grazers to improve coral nursery performance and reduce maintenance costs.

Culturing reef-building corals on a laboratory dish: a simple experimental platform for stony corals

Development and maintenance of coral reef ecosystems rely on daily micro-biological activities of healthy corals. Although a comprehensive understanding of coral biological properties, as well as factors negatively affecting coral growth, are essential to conserve existing corals, the current lack of a tractable culture and experimental platform has delayed acquisition of such knowledge. Here we show a highly versatile culture system, “coral-on-a-laboratory dish” (CLD), allowing long-term culturing of various corals in plastic/glass Petri dishes with maintenance of their biological properties. Under optimized conditions, coral microcolonies (~5 mm x 5 mm fragments) of Pocillopora damicornis were cultured for several months in dishes with high survivorship and characteristic growth. These microcolonies maintained their biological properties, such as reproduction, skeleton formation, coral-algal symbiosis, ingestion, and digestion. Thus far, CLD has been used to maintain at least 4 other coral species from 4 other families, including the Acroporidae, the Pocilloporidae, the Poritidae, and the Merulinidae for more than 2 months with 100% survivorship. CLD is applicable to a variety of biophysiological studies, including coral-algal symbiosis and impact assessment of marine pollutants, e.g., a sunscreen substance, oxybenzone, and an organic biocide, Irgarol 1051, at cellular-level resolution. The CLD platform, which allows easy and inexpensive coral maintenance in a laboratory incubator, represents a technological breakthrough that will greatly advance coral studies.

Visual Surveys Reveal Coral Growth in Mangrove Fringe in a Subtropical Metropolis

Mangrove forests are understudied habitats for potentially resilient coral communities (Rogers 2019, Stewart et al. 2022). These coexisting mangrove-coral (CMC) habitats (Stewart et al. 2022) can be found around the world yet are still underreported and understudied. Miami, Florida falls within the possible range of CMC habitat distribution (see figure 7 in Stewart et al. 2022) but is also a heavily urbanized coastal environment. We conducted surveys of potential CMC habitats in the spring and summer of 2022 at four locations: Lamar Lake, Bill Sadowski Critical Wildlife Area, Matheson Hammock Park and Marina, and Bill Baggs Cape Florida State Park ("Bill Baggs"). Approximately 3 km of coastline were explored using rudimentary visual surveys conducted via.

Symbiodiniaceae Density Pattern in Relation To Colony Morphology of Scleractinian Corals in Pulau Tioman and Pulau Bidong, Malaysia

A healthy coral reef is linked to the mutualistic relationship between scleractinian coral and the symbiotic Symbiodiniacea (SD). However, there is limited research on SD in Malaysia, despite its important role in reef-building coral. In this study, the SD density of scleractinian corals from the family Acroporidae was evaluated to (i) examine the pattern of SD density and (ii) comprehend the regulation of the SD density by the host. The mean SD density ranged between 0.46 ± 0.01 × 106 cell cm-2 and 2.98 ± 1.17 × 106 cell cm-2. It is hypothetically proven that the SD density differed significantly between genera and morphological factors such as colony surface area (CSA) and dry weight coral tissue per unit colony surface area (DWCT/CSA) were significantly correlated with the SD density. The results show that the significant variation in SD density among coral genera can be influenced by coral growth forms and tissue biomass. There was a significant relationship between SD density and CSA as well as DWCT/CSA. Coral genera with a wider CSA and lower DWCT/CSA such as Anacropora and Acropora with branching, digitate and tabulate growth forms contained lower SD density than massive, laminar, and encrusting such as Montipora and Astreopora which hold more DWCT/CSA at lower CSA, resulting in higher SD density. The findings provide valuable information on SD density in different types of corals from the southern part of the South China Sea and reveal the coral host’s SD regulation.

Condition of coral cover area in the northern region of Tidung Kecil Island, Thousand Islands

This study aims to determine the condition of the coral reef ecosystem on Tidung Kecil Island, Seribu Islands. Observational data collection was carried out in June 2022. The method used in this study was descriptive with the Line Interval Transect (LIT) technique with two repetitions, with the distance between the transect points being 10 meters. 2 repetitions aim to represent the coral cover data on the island's northern part. The data taken are the length and type of coral reef growth, which is then processed to be included in the coral cover area formula. Observational data were then analyzed using the coral cover percentage formula to calculate live coral growth and continued calculating the percentage cover for all categories of live coral lifeforms. Based on the observations, the condition of the coral cover area in the study area is classified as bad, with a percentage of coral cover area of 18.63% and a percentage of non-coral substrate of 48.7%. This is due to the high human activity (such as fishing) and tourism (such as snorkeling).