Turbinaria Mesenterina Research Articles

Microplastics elicit an immune-agitative state in coral

Microplastic pollution in the ocean is a major problem, as its pervasiveness elicits concerns the health impacts microplastics may have on marine life (such as reef-building corals). As a primary endpoint, the organismal lipidome can define the weakening of fitness and reveal the physiological context of adverse health effects in organisms. To gain insight into the effects of microplastics on coral health, lipid profiling was performed via an untargeted lipidomic approach on the coral Turbinaria mesenterina exposed to ~10 μm polystyrene microparticles for 10 days. Considerable microplastic accumulation and obvious effects relating with immune activation were observed in the coral treated with a near environmentally relevant concentration of microplastics (10 μg/L); however, these effects were not evident in the high level (100 μg/L) treatment group. In particular, increased levels of membrane lipids with 20:4 and 22:6 fatty acid chains reallocated from the triacylglycerol pool were observed in coral host cells and symbiotic algae, respectively, which could upregulate immune activity and realign symbiotic communication in coral. High levels of polyunsaturation can sensitize the coral cell membrane to lipid peroxidation and increase cell death, which is of greater concern; additionally, the photoprotective capacity of symbiotic algae was compromised. As a result, coral physiological functions were altered. These results show that, realistic levels of microplastic pollution can affect coral health and should be a concern.

First record of patchy coral reef off Terekhol, North Goa, India

This study reports the first time record of the patchy coral reef (~ 2 km2) of Terekhol in North Goa, the western coast of India during January – February 2020. There were more than 07 genera/species of hard corals in the reef and is dominated by a reef building Turbinaria mesenterina (Dendrophylliidae), which is considered as a sediment tolerant coral species. A total of 25 fish species were counted and the major species recorded were Chromis viridis, Chromis sp., Dascyllus sp., Abudefduf saxatilis, Abudefduf bengalensis, Acanthurus blochii, Acanthurus nigroris, Acanthurus sp., and Odonus niger that contributed 80 % of the total fish community. The documentation and record of the reef area could give identity to the ecosystem in the spatial platform and the conservation efforts can be planned for the reef by limiting the anthropogenic activities in and around the ecosystem.

Impact of short-term light variability on the photobiology of turbid water corals

Benthic light availability is readily affected by natural drivers of an ecosystem and by anthropogenic-induced stressors. Rapid urbanization in coastal regions can induce light variability for reef-building corals that use photosynthesis as a primary form of energy. However, very little data exists on the photosynthesis of light-limited coral species and their acclimation responses to an additional light variability. This experimental study explored the effects of two contrasting light intensities: high light (HL) (95% increase to in situ light) and low light (LL) (8–10% of in situ light) on three locally dominant coral species. Turbinaria mesenterina, Porites lutea, and Goniopora cellulosa were collected from a 4-m depth from the turbid regions of Pulau Kendi in Northern Peninsular Malaysia. This study documented current photobiological responses of all species and rapid photoacclimation responses only for T. mesenterina in HL treatment. All three species incurred photoinactivation under LL stress; however, T. mesenterina was photosynthetically healthier for an extended period of the experiment. P.lutea recorded partial photoacclimation and non-recovering photoprotectants to both light stresses. While G. cellulosa incurred rapid declines in photosynthetic yields along with no photoacclimation responses. The data obtained for this geographic range of turbid water corals is important as additional light stress from point-source pollutants and global urbanization activities are expected to increase. Improving our understanding of their responses to environmental change will be central to global coral reef conservation efforts andcan be used for effective management practices in targeted coral conservation and rehabilitation approaches for turbid habitats.

Differential Symbiodiniaceae Association With Coral and Coral-Eroding Sponge in a Bleaching Impacted Marginal Coral Reef Environment

Marginal reefs are known for severe stress-inducible perturbations such as high sedimentation, eutrophication, ocean warming, and acidification from anthropogenic climate change. The corals striving in such stressful environments develop physiological adaptations induced by differential genomic expressions or association with thermal stress-tolerant algal symbionts (Symbiodiniaceae). Despite such adaptations, corals are threatened by other space competitors such as algae and sponges. Coral-eroding sponges belonging to the Cliona viridis complex are one such space competitors that also associate with Symbiodiniaceae algal photosymbiont. The diversity of Symbiodiniaceae associates with the coral and sponge from the same ecosystems is scarcely known. In the present study, Symbiodiniaceae community structure in the coral Turbinaria mesenterina, a newly described coral-eroding sponge Cliona thomasi, and their surrounding seawater was determined from the nearshore marginal reef along the central west coast of India. The results revealed a significantly higher relative abundance of Durusdinium and Gerakladium than Symbiodinium and Cladocopium in the seawater. Interestingly, both investigated host species showed differential Symbiodiniaceae association with significantly higher abundance of Durusdinium in coral and Gerakladium in sponge. The beta diversity analysis by Permutational multivariate analysis of variance (PERMANOVA) confirmed significant differences in Symbiodiniaceae profiles between sponge and coral. Durusdinium and Gerakladium are thermotolerant genera known to associate with different hosts in suboptimal conditions. Our field surveys suggested the bleaching resistance of the coral T. mesenterina despite the fact that the sea surface temperature reached the coral thermal threshold of 31°C during different periods of the years 2015, 2016, 2017, 2018, and 2019. Therefore, the thermal tolerance of the investigated coral and sponge species may be attributed to their respective thermotolerant photosymbiont associations. Furthermore, the results also indicated the host-specific photosymbiont selection from the local environment. Although these observations provide valuable biological insight, more research is needed to understand the tripartite association of sponge-coral-symbiont together to evaluate the competitive fitness of holobionts.

Interactions between coral propagules in aquarium and field conditions

The effects of intraspecific and interspecific interactions between three species of scleractinian coral micro-colonies, namely Lithophyllon undulatum, Turbinaria mesenterina and Platygyra sinensis were evaluated for their survivorship, tissue loss and growth in both field (in-situ) and aquarium (ex-situ) conditions over 12 weeks. Regardless of environmental conditions and interactions, L. undulatum survived better (91.7 ± 6.2%) than T. mesenterina (75.0 ± 25.0%) and P. sinensis (60.4 ± 39.5%). Similarly, L. undulatum registered the lowest tissue loss (0.5 ± 0.7%) as compared to T. mesenterina (14.3 ± 19.4%) and P. sinensis (22.0 ± 30.0%). However, P. sinensis gained more weight (3.2 ± 5.2 g) than either T. mesenterina (2.7 ± 2.4 g) or L. undulatum (0.8 ± 1.1 g). In both environments, all three species in intraspecific interaction generally had higher survivorship, lower tissue loss and better growth than those in interspecific interaction except the latter in in-situ conditions had a twofold increase in growth (5.8 ± 3.7 g) than the former in-situ conditions (2.8 ± 3.7 g). Hence, all three species are potentially suitable for transplantation and mariculture except perhaps for P. sinensis which performed poorly in ex-situ conditions. Corals can be transplanted either with different colonies of the same species or together with other coral taxa. This study demonstrated that L. undulatum should be transplanted between T. mesenterina and P. sinensis for optimal growth and survival.

Optimal temperature regimes for land‐based mariculture of tropical corals

Thermal tolerances of ten coral taxa in relation to their survivorship, health status and growth performance were examined. These coral microcolonies were subjected to temperatures of 26°C, 28°C, 30°C and 32°C for 2 months in an indoor recirculating aquaculture system (RAS). Not unexpectedly, most coral species tested thrived well between 28°C and 30°C, except for Acropora valida which fared best at 26°C. However, subtle differences were apparent. Turbinaria mesenterina, Porites lobata/lutea, Pachyseris speciosa, Platygyra sinensis, Porites rus and Pavona frondifera thrived well at 28°C whilst Dipsastraea speciosa, Pocillopora acuta and Podabacia crustacea, together with Tur. mesenterina and Pla. sinensis, performed better at 30°C. Only Tur. mesenterina and Pod. crustacea survived at 32°C. Amongst the coral taxa tested, Pla. sinensis depicted the highest growth rate of 1.4 mm/month at 30°C, followed by Tur. mesenterina at 30°C and Pod. crustacea at 28°C where both grew at 1.0 mm/month. Dip. speciosa, Pla. sinensis and Pod. crustacea cultured at 30°C were the least bleached. In response to elevated temperatures, the survival of laminar corals outperformed massive and branching corals. This thermal study suggests that all species tested can be ex situ propagated in RAS and Tur. mesenterina and Pod. crustacea are also suitable for transplantation.

Massive coral bleaching in the patchy reef of Grande Island, along the eastern Arabian Sea during the 2015/16 global bleaching event

The 2014–2017 mass bleaching event is considered the third massive coral global bleaching event in recorded history. Based on the National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch (CRW) product western India was under an alert level 2 (May–June 2015) with ten-Degree Heating Weeks (DHW) followed by level 1 (six-DHW) from October–November 2015. In succession to our regular surveys, we conducted intensive bleaching surveys following the bleaching alerts issued by NOAA to quantify the coral bleaching in Grande Island along the eastern Arabian sea during October–November2015. The in-situ observations of massive bleaching (∼50%) during the predicted bleaching period by NOAA CRW for the study area contrasted with a lower prevalence of bleaching before (6%) and after (8%) the event. Bleaching severity was highest in Porites spp. corals and the least in foliose Turbinaria mesenterina. The long-term effects of bleaching in this area remain to be seen. This study is the first record of massive bleaching and quantitative assessment in patchy reefs along the eastern Arabian Sea and would act as a baseline data for further reef studies.

APPLICATION OF UNDERWATER PHOTO TRANSECT METHOD TO UNDERSTAND CORAL REEFS COVER IN POMBO ISLAND, MALUKU

Methods to understand coral reefs health are increasingly diverse. One of the promising method is georeferenced photo transect. In this method, a diver took benthic community photos using a camera installed or connected with a Global Positioning System (GPS) receiver, so that each photo taken has a geographic coordinate on it. This spatial information is very useful for monitoring coral reefs health. The purpose of this research is to understand coral reefs cover in Pombo Island, Maluku by using georeferenced photo transect method. Field data collection was done in April 2015 with 14 transect lines. Overall of 14 transect lines, 3 transects are in Good category, other 3 transects are in Pretty Good category, and the rest of 8 transects are in Not Good category. Coral species commonly found around transect lines are Porites lutea, Porites lobata, Acropora valenciennesi, Acropora hyacinthus, Turbinaria mesenterina, Stylophora pistillata, Mycedium elephantotus, Acropora latistella

Prevalence of skeletal tissue growth anomalies in a scleractinian coral: Turbinaria mesenterina of Malvan Marine Sanctuary, eastern Arabian Sea.

Skeletal tissue growth anomalies (STAs) of corals are capable of causing considerable degradation of reef health. This study is the first report of growth anomalies in Turbinaria corals and the first descriptive study of Indian corals. T. mesenterina colonies at 2 sites were affected by small, round to irregularly shaped growth anomalies. Prevalence of STAs was observed to be higher in T. mesenterina colonies with larger diameters. Prevalence of STAs on T. mesenterina was 71% at Site 1 and 40% at Site 2. Affected colonies were seen to be undergoing tissue damage and infiltration by filamentous algae. We describe the gross morphology of growth anomalies which can act as baseline data for growth anomalies from this region, but further investigation is needed to understand the form and etiology of this coral disease.

Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand

A long-term study of coral reef ecology in the Gulf of Thailand provides a good opportunity to examine the temporal variation on the impact of mass coral bleaching at those reef sites. We compared the bleaching and mortality of corals between the mass bleaching events in 1998 and 2010 at a coral community in the Western Gulf of Thailand. The aim was to identify the coral species which were most likely to suffer from (and to be able to tolerate) changes in seawater temperature. Significant differences in the susceptibility of the coral taxa to bleaching events between the years 1998 and 2010 and among coral species were documented. Bleaching was significantly different between the most dominant corals. Diploastrea heliopora was the most resistant coral to bleaching in both years. Some coral species showed more resistance to bleaching in 2010. The coral mortality following the mass bleaching events in 1998 and 2010 varied significantly between the years and the coral taxa. Mortality of some dominant coral taxa was also lower in 2010. Seven coral species, i.e. Astreopora myriophthalma, Pachyseris rugosa, Turbinaria mesenterina, Goniastrea pectinata, Favia pallida, F. maritima, Favites halicora, Platygyra daedalea and Galaxea fascicularis, were tolerant to the coral bleaching events. An ecosystem-based approach to managing coral reefs in the Gulf of Thailand is needed to identify appropriate marine protected area networks and to strengthen marine and coastal resource policies in order to build coral reef resilience.

The Role of Coral-Associated Bacterial Communities in Australian Subtropical White Syndrome of Turbinaria mesenterina

Australian Subtropical White Syndrome (ASWS) is an infectious, temperature dependent disease of the subtropical coral Turbinaria mesenterina involving a hitherto unknown transmissible causative agent. This report describes significant changes in the coral associated bacterial community as the disease progresses from the apparently healthy tissue of ASWS affected coral colonies, to areas of the colony affected by ASWS lesions, to the dead coral skeleton exposed by ASWS. In an effort to better understand the potential roles of bacteria in the formation of disease lesions, the effect of antibacterials on the rate of lesion progression was tested, and both culture based and culture independent techniques were used to investigate the bacterial communities associated with colonies of T. mesenterina. Culture-independent analysis was performed using the Oligonucleotide Fingerprinting of Ribosomal Genes (OFRG) technique, which allowed a library of 8094 cloned bacterial 16S ribosomal genes to be analysed. Interestingly, the bacterial communities associated with both healthy and disease affected corals were very diverse and ASWS associated communities were not characterized by a single dominant organism. Treatment with antibacterials had a significant effect on the rate of progress of disease lesions (p = 0.006), suggesting that bacteria may play direct roles as the causative agents of ASWS. A number of potential aetiological agents of ASWS were identified in both the culture-based and culture-independent studies. In the culture-independent study an Alphaproteobacterium closely related to Roseovarius crassostreae, the apparent aetiological agent of juvenile oyster disease, was found to be significantly associated with disease lesions. In the culture-based study Vibrio harveyi was consistently associated with ASWS affected coral colonies and was not isolated from any healthy colonies. The differing results of the culture based and culture-independent studies highlight the importance of using both approaches in the investigation of microbial communities.

Seasonality of coral reproduction in the Dampier Archipelago, northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.

Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina

Water quality is declining in many coastal areas, which has caused coral degradation worldwide. In addition, reduced water quality may aggravate the impacts of seawater temperature. In this study the effects of increased temperature (31 °C), nitrate enrichment (+5 μM NO 3 −), low salinity (20) and combinations of these stressors were investigated compared to ambient water (25 °C, 30, 0.3 μM NO 3 −) on the metabolism and survival of the coral Turbinaria mesenterina from the Tonkin Gulf, Vietnam. The results showed that all specimens exposed to a combination of all three stressors (i.e. high temperature + high nitrate + low salinity) died after 24 h exposure, while those that had been exposed to high nitrate + low salinity at ambient temperature did not show any effects on the metabolism or survival. Furthermore, corals exposed to low salinity + high temperature displayed a decrease in gross primary production/respiration (GP/R) ratio and the mortality rate was 50%. In addition, all corals exposed to increased temperature, alone or in combination with another stressor, displayed a GP/R 24h ratio below 1.0, suggesting that they depend on stored energy to cover their metabolic requirements. The results showed that corals may tolerate short-term exposure to stressors such as low salinity + high nitrate concentration in ambient temperature, while additional increased temperature lead to rapid mortality, hence suggesting a synergistic effect. Thus, the effect of climate change might be more severe in nearshore coastal areas where corals already are exposed to several disturbances.

Australian subtropical white syndrome: a transmissible, temperature-dependent coral disease

Since 2000, a disease displaying white-syndrome characteristics has been observed affecting corals from the genus Turbinaria in the Solitary Islands Marine Park, New South Wales, Australia. Recently termed Australian subtropical white syndrome, this disease is transmissible through direct contact and by a predatory vector, but transmission through the water column has not been observed. In aquarium experiments, progressive tissue loss, extending from the region where healthy Turbinaria mesenterina fragments were in direct contact with samples of diseased coral, was noted in 66% of treatments. No tissue loss occurred in any of the controls or when healthy fragments were not in direct contact with diseased corals. Field experiments confirmed that the disease was infectious through direct contact. Further experiments showed that the rate of tissue loss was significantly higher when corals were exposed to summer temperatures (26°C). These results suggest that temperature increases predicted in most climate change models could lead to the loss of dominant coral species, displacing other organisms that rely on corals for food and shelter. Finally, the present study showed that removal of the disease margin provides a management tool to minimise coral tissue loss during an epizootic.

Effects of photoacclimation on the light niche of corals: a process-based approach

The ecology of photosynthetic organisms is influenced by the need to adjust the photosynthetic apparatus to variable light environments (photoacclimation). In this study, we quantified different components of the photoacclimation process for a reef-building coral (Turbinaria mesenterina, Lamarck, 1816): including, variation in absorption cross-section, size of photosynthetic units, turnover time, chlorophyll content, and colony respiration. We used these calibrations to characterize this species’ light niche, and to determine the sensitivity of the niche boundaries to different processes of photoacclimation. Results showed that the breadth of the light niche was most sensitive to the size of the photosynthetic unit, absorption cross-section, and rates of respiration. Habitats with the highest light availability did not lead to maximal energy acquisition. This was because, although corals acclimated to high light have high rates of photosynthesis per unit chlorophyll, their chlorophyll content was strongly reduced. This suggests that potential energetic benefits that could be achieved through increased light harvesting (i.e., increased chlorophyll content) in high-light habitats are outweighed by costs associated with photoprotection. Such costs appear to place an upper bound on the habitat distributions of coral species. Our approach reveals how the photophysiological processes involved in photoacclimation interact to determine the light niche.

High-sediment tolerance in the reef coral Turbinaria mesenterina from the inner Great Barrier Reef lagoon (Australia)

Sedimentation is an important stressor on coral reefs subjected to run-off, dredging and resuspension events. Reefs with a history of high-sediment loads tend to be dominated by a few tolerant coral species. A key question is whether such species live close to their tolerance thresholds or near their niche optima. Here, we analyse experimentally the sediment tolerance of a spatially dominant coral, Turbinaria mesenterina (Dendrophylliidae), at nearshore reefs in the central Great Barrier Reef lagoon. Testing was conducted in a 5-week tank experiment under manipulated sediment loading and flow conditions. Physiological stress was assessed based on the behaviour of three key response variables: skeletal growth rate, energy reserves (lipid content) and photosynthetic performance. Because sediment effects are likely to vary between flow regimes, sediment and flow responses were tested using a full factorial design. Sediment loads greater than 110 mg cm −2 had no effect on any of the physiological variables, regardless of flow (0.7–24 cm s −1). Turbinaria mesenterina is thus tolerant to sediment loads an order of magnitude higher than most severe sediment conditions in situ. Likely mechanisms for such tolerance are that: (1) colonies covered in sediment (60–120 μm) in low-flow were able to clear themselves rapidly (within 4–5 h); and (2) sediment provides a source of food. These results suggest that intensified sediment regimes on coastal reefs may shift coral communities towards dominance by a few well-adapted species.

Coral bleaching, bleaching-induced mortality, and the adaptive significance of the bleaching response

Coral bleaching events are often associated with higher levels of coral mortality but when this occurs in the chronology of individual bleaching events is poorly documented. Knowing when mortality occurs is important for understanding molecular mechanisms and the putative adaptive significance of the response (the Adaptive Bleaching Hypothesis). In a detailed study of a coral bleaching event on the Great Barrier Reef, involving weekly and twice weekly repetitive observations of >200 individually marked corals over an 18 month period (∼16,000 observations), it is shown that bleaching in Acropora latistella, A. subulata and Turbinaria mesenterina was an acute, rapid response, occurring within days of a peak in seawater temperatures exceeding previously described thresholds. Subsurface light levels, measured over the duration of the event, were not anomalous. Full bleaching (i.e. whole colonies turning bone-white) and partial bleaching (white patches) was observed in the Acropora spp. whilst the T. mesenterina colonies typically paled to a light brown colour. Algal densities in bleached corals were 10–30% of those of normally pigmented corals (∼2.5 × 106 algae per cm2), and in this instance bleaching was clearly a sudden, isolated, stress event and not an extreme low-point in the seasonal fluctuation of the density of symbiotic algae. Bleached corals were associated with high levels of partial and whole-colony mortality, but mortality was exclusively limited to the two Acropora spp. Importantly, most of this mortality was recorded in surveys conducted 1 and 2 weeks after bleaching was first observed, and for A. latistella as little as 1 week after bleaching was first observed. This suggests that in this particular bleaching event, for the Acropora species, that bleaching and mortality were intimately linked: this in turn suggests it was a pathological phenomenon. The study highlights a problem in the adaptive bleaching hypothesis, whereby significant levels of mortality can occur in a bleaching event before any chance for subsequent recombination of the host-symbiont unit. It is argued that in order to further evaluate the significance of bleaching as a potentially adaptive mechanism, bleaching-induced and bleaching-related mortality have to be fully considered. It is necessary to incorporate the cost (in terms of mortality) of a bleaching event, the recurring cost of reverting to the original, mortal, stress–prone combination after the event, and the higher cost associated with forming a maladaptive combination.

Enhanced energy status of corals on coastal, high-turbidity reefs

Sedimentation and high turbidity have long been considered a major threat to corals, causing world-wide concern for the health of coral reefs in coastal environments. While studies have demonstrated that sediment conditions characteristic of inshore reefs cause stress in corals, the consequences of such conditions for the physiological status of corals require testing in field situations. Here, I compare the size of energy stores (as lipid content), a proxy for physiological condition, of 2 coral species (Turbinaria mesenterina and Acropora valida) between coastal and offshore environments. Corals on coastal reefs contained 4-fold (T. mesenterina) and 2-fold (A. valida) more lipid than conspecifics offshore, despite 1 order of magnitude higher turbidity levels inshore. Results were consistent across 4 sites in each environment. Reproductive investment in A. valida (a seasonal mass spawner) did not vary between environments, suggesting that the larger lipid stores in corals on coastal reefs are mainly somatic energy reserves. These results demonstrate that the environmental conditions on inshore, high-turbidity reefs do not always impact negatively on the physiology of corals. The contrasting lipid levels of T. mesenterina between environments may explain its greater success on coastal reefs.

Energetic cost of photoinhibition in corals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 313:1-12 (2006) - doi:10.3354/meps313001 Energetic cost of photoinhibition in corals Mia O. Hoogenboom*, Kenneth R. N. Anthony, Sean R. Connolly ARC Centre of Excellence for Coral Reef Studies, and School of Marine Biology and Aquaculture, James Cook University, Townsville, Queensland 4811, Australia *Email: mia.hoogenboom@jcu.edu.au ABSTRACT: Photoinhibition may constitute an energetic cost for photosynthetic organisms through damage to the photosynthetic apparatus, or by increased metabolism due to damage avoidance or repair. For several species of scleractinian corals, fluorescence techniques have revealed a significant reduction in photochemical efficiency of symbiotic dinoflagellates within coral tissue in response to excess light absorption. To date, it has been unclear whether or not photoinhibition has a negative impact on energy budgets in corals. We simultaneously quantified the effect of exposure to excessive light on net rates of photosynthesis and on fluorescence-derived photochemistry. We acclimated colonies of the reef-building coral Turbinaria mesenterina to 3 different irradiance regimes in the laboratory. The corals were then exposed to light levels up to 10 times higher than their acclimation irradiance and assayed for rates of photosynthesis and photochemical yields. Results indicated that daily costs of photoinhibition are negligible. Reduced net rates of photosynthesis in the afternoon, compared to the morning, were predominantly due to enhanced afternoon rates of dark respiration. However, photoacclimation to high light levels reduces daily energy acquisition in the long term, primarily due to decreased chlorophyll concentrations. Therefore, although changes in the photosynthetic activity of symbiotic dinoflagellates over a diurnal irradiance cycle do not cause a measurable decline in net oxygen evolution for coral colonies, repeated exposure to excessive irradiance can reduce energy acquisition per unit surface area, and hence influence the upper limit of the depth distribution of scleractinian corals. KEY WORDS: Photoinhibition · Respirometry · PAM fluorescence · Scleractinian coral · Energy budget · Photosynthetic efficiency · Turbinaria mesenterina Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 313. Online publication date: May 11, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Adaptive variation in coral geometry and the optimization of internal colony light climates

Summary The ability of photosynthetic organisms to adjust their light climate has high adaptive significance because irradiance can vary spatially by orders of magnitude. Using a plating (foliaceous) coral species (Turbinaria mesenterina), we tested the hypothesis that plasticity of colony geometry optimizes internal irradiance distributions. We developed a two‐dimensional model to predict the internal irradiance distribution of a foliaceous colony as a function of its geometry. Field tests showed that the model explained 85% of the variation in irradiance within colonies of T. mesenterina with minimal bias. Colony plate angle, plate spacing and range of tissue distributions into the colony were exponential functions of water depth. In shallow water plates tended to be nearly vertical, narrowly spaced, and had living tissue only near the growing edge of the plate. In deep water plates grew more horizontally, were more widely spaced, and had living tissue extending well into the colony interior. This pattern of phenotypic plasticity effectively evens out differences in within‐colony irradiances. We compared within‐colony irradiance distributions across light habitats (depth), based on the observed variation in colony geometry with water depth. Despite fourfold differences in environmental irradiance, within‐colony irradiances had a common mode of 100–200 µmol m−2 s−1. This is near the hypothesized photosynthetic optimum defined by the upper limit of the subsaturation parameter (Ek) of the photosynthesis–irradiance curve. Our study demonstrates that phenotypic plasticity of colony geometry is an important mechanism for regulating light capture during growth in T. mesenterina, and facilitates near‐optimal internal irradiances across a wide range of environmental light regimes.