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Fast repetition rate (FRR) fluorometry: Variability of chlorophyll a fluorescence yields in colonies of the corals, Montastraea faveolata (w.) and Diploria labyrinthiformes (h.) recovering from bleaching
Abstract
Recently, an underwater version of a fast repetition rate fluorometer (FRRF) was developed for the non-destructive study of fluorescence yields in benthic photoautotrophs. We used an FRRF to study bleached colonies of the corals, Montastraea faveolata and Diploria labyrinthiformes at sites surrounding Lee Stocking Island, Exuma, Bahamas, to assess their recovery from bleaching (∼1 year after the initial bleaching event) induced by elevated temperatures. The steady state quantum yields of chlorophyll a fluorescence (ΔF′/F′m) from photosystem II (PSII) within coral colonies were separated into three categories representing visibly distinct degrees of bleaching ranging from no bleaching to completely bleached areas. Differences in ΔF′/F′m were significantly different from bleached to unbleached regions within colonies. Dark, unbleached regions within colonies exhibited significantly higher ΔF′/F′m values (0.438±0.019; mean±S.D.) when compared to lighter regions, and occupied a majority of the colonies’ surface area (46–73%). Bleached regions exhibited significantly lower ΔF′/F′m (0.337±0.014) and covered only 7–25% of the colonies’ surface area. The observations from this study suggest that zooxanthellae in bleached regions of a colony exhibit reduced photosynthetic activity as long as one year after a bleaching event and that in situ fluorescence techniques such as FRRF are an effective means of studying coral responses and recovery from natural or anthropogenic stress in a non-destructive manner.
... Thus, short-term dynamic depression of the quantum yield could not be assessed. With a newly developed underwater fluorometer (Diving-PAM; Schreiber et al., 1997), or a SCUBA-based fast repetition rate fluorometer (FRR-fluorometer) (Gorbunov et al. 2000) it is now possible to perform underwater measurements of the effective quantum yield in benthic organisms in situ. This gives information on how photosynthesis is regulated under water in relation to the impinging fluence rate. ...
... The FRR-fluorometer measures, in contrast to the Diving-PAM, chlorophyll fluorescence transients using a controlled series of sub-saturating blue light flashes that cumulatively saturate PS II within about 100µs, i.e. within a single photochemical turnover. The optimal quantum yield of brown algae determined with this fluorometer seems to be somewhat lower than determined with a PAM-fluorometer (Gorbunov et al. 2000). As yet only measurements in corals have been published using this instrument (e.g. ...
... As yet only measurements in corals have been published using this instrument (e.g. Lesser and Gorbunov 2001;Lombardi et al. 2000). Investigations of corals, sponges and macrophytes using the Diving-PAM are already well established (Beer and Illan, 1998;Beer et al., 1998aBeer et al., ,b, 2000Schreiber et al., 1997) and many more will be surely done in future times. ...
Marine macrophytes live in a highly variable environment in respect to light, UV-radiation, temperature and also salinity.
During evolution their metabolism has adapted to these strongly changing conditions, especially in the upper littoral zone.
In the lower subtidal, the photosynthetic apparatus has adapted to low light conditions, to absorb maximally the incident
photons and to utilize the absorbed energy with high efficiency. In the intertidal and upper sublittoral zone the photosynthetic
apparatus is exposed to strong light stress when the absorbed amount of light energy is higher than the organism can use for
its metabolism. This happens generally when plants are exposed to irradiances, which are above the mean level of irradiation
occurring at their growth sites (e.g., light flecks or low tide around noon). Under light stress the amount of thermal energy
dissipation increases and the energy flowing into photochemistry decreases also. Photoinhibition causes a decrease of the
photosynthetic quantum yield (dynamic inhibition) and at much higher fiuence rates or after a longer duration of high irradiation,
also a decrease of the photosynthetic capacity (chronic inhibition). The absorption cross- section of the chromatophores can
be diminished by chloroplast displacement or shrinking, especially in brown algae, which decreases the rate of photodamage
to the light-absorbing apparatus. Irradiances, which exceed the protective capacities of these mechanisms, cause irreversible
damage to the photosynthetic apparatus. Normally, the latter does not occur for long at the natural growth sites.
... The isotopic fractionation and δ 13 C of symbiotic zooxanthellae (δ 13 C z ) are largely regulated by the photosynthesis intensity of symbiotic zooxanthellae, which is closely related to the zooxanthellae density (ZD) level. Decreases in ZD level is accompanied by a net decrease in photosynthesis and δ 13 C z , and vice versa (Grottoli et al., 2004;Lombardi et al., 2000;Muscatine et al., 1989;Porter et al., 1989;Warner et al., 2002). The δ 13 C of coral host tissues (δ 13 C h ) is mainly affected by the heterotrophic predation of coral host. ...
... Therefore, we suggest that the higher photosynthesis intensity of genera Porites, Favites, and Favia compared to the genus Pavona and genus Acropora was mainly caused by their higher ZD. This result is consistent with previous studies that changes in algal symbiont densities and/or Chl a levels are accompanied by changes in photosynthesis intensity Lombardi et al., 2000;Warner et al., 2002;Xu, Yu, Tao, et al., 2018). Similar situation had also been reported in previous studies, such as the δ 13 C z of the nonbranching corals with higher ZD are heavier than that of branching corals with lower ZD, due to the different photosynthesis intensity of their symbiotic zooxanthellae (Muscatine et al., 1989;Porter, 1976). ...
The knowledges of trophic status (i.e., autotrophy/heterotrophy) of corals are helpful for understanding the mechanisms driving their environmental stress tolerance and bleaching resilience. We conducted this study to elucidate the differences in trophic status among corals of different genera and then explore the implication of trophic status for their different environmental stress tolerance. In this study, 117 coral samples including five genera (i.e., relatively stress‐tolerant massive genera Porites, Favites, and Favia and relatively vulnerable plating genus Pavona and branching genus Acropora) were collected from Weizhou Island, northern South China Sea. The symbiotic zooxanthellae density, δ¹³C of host tissues (δ¹³Ch), and symbiotic zooxanthellae (δ¹³Cz) were measured. Besides, the difference in values between δ¹³Ch and δ¹³Cz (i.e., △h‐z 13C) was analyzed. Our results indicated that both zooxanthellae density and δ¹³Cz values of Porites, Favites, and Favia are higher than that of Pavona and Acropora and indicate that autotrophic photosynthesis intensity of symbiotic zooxanthellae of Porites, Favites, and Favia is higher than that of Pavona and Acropora. Besides, both δ¹³Ch and △h‐z 13C of Porites, Favites, and Favia are lower than that of Pavona and Acropora and indicate a higher contribution of heterotrophic predation to the coral host of Porites, Favites, and Favia. These comparisons suggest that trophic status of relatively stress‐tolerant Porites, Favites, and Favia is more plasticity than vulnerable Pavona and Acropora, which is conducive to maintain a positive energy budget. This is one of important factors leading to different environmental stress tolerance and bleaching resilience among corals of different genera.
... In bleached corals, decreases in algal symbiont densities and/or chl a levels are accompanied by a net decrease in photosynthesis Fitt and Warner 1995;Lesser 1997;Lombardi et al. 2000;Warner et al. 2002). Under these circumstances, corals may rely heavily on their energy stores to support their metabolic energy needs. ...
... Coral color is correlated with chl a concentration (Edmunds et al. 2003) and is commonly used to identify non-bleached and bleached corals (e.g. Jokiel and Coles 1974;Lombardi et al. 2000;Edmunds et al. 2003). Some coral colonies were not uniformly affected, but were bleached white on the top, while their sides were a healthy, non-bleached dark brown. ...
Mass coral bleaching events have occurred on a global scale throughout the worlds tropical oceans and can result in large-scale coral mortality and degradation of coral reef communities. Coral bleaching has often been attributed to periods of above normal seawater temperatures and/or calm conditions with high levels of ultraviolet radiation. Unusually high shallow-water temperature (>29C) in Kaneohe Bay, Hawaii, USA, in late summer (20 August–9 September) and fall (1–7 October) of 1996 produced visible bleaching of two dominant corals, Porites compressa Dana, 1864 and Montipora verrucosa Dana, 1864. The present study examined chlorophylla (chla), total lipid concentrations, and lipid class composition in corals of both species in which the entire colony was non-bleached, moderately bleached, or bleached. Skeletal, host tissue, and algal symbiont 13C values were also measured in non-bleached and bleached colonies. In additional unevenly bleached colonies, paired samples were collected from bleached upper surfaces and non-bleached sides. Samples were collected on 20 November 1996 during the coral recovery phase, a time when seawater temperatures had been back to normal for over a month. Chla levels were significantly lower in bleached colonies of both species compared with non-bleached specimens, and in bleached areas of unevenly bleached single colonies. Total lipid concentrations were significantly lower in bleached P. compressa compared with non-bleached colonies, whereas total lipid concentrations were the same in bleached and non-bleached M. verrucosa colonies. The proportion of triacylglycerols and wax esters was lower in bleached colonies of both species. Both bleached and non-bleached M. verrucosa had from ~17% to 35% of their lipids in the form of diacylglycerol, while this class was absent in P. compressa. 13C was not significantly different in the host tissue and algal symbiont fractions in non-bleached and bleached samples of either species. This suggests that the ratio of carbon acquired heterotrophically versus photosynthetically was the same regardless of condition. Skeletal 13C was significantly lower in bleached than in non-bleached corals. This is consistent with previous findings that lower rates of photosynthesis during bleaching results in lower skeletal 13C values. The two species in this study displayed different lipid class compositions and total lipid depletions following bleaching, suggesting that there is a difference in their metabolism of lipid reserves and/or in their temporal responses to bleaching and recovery.
... Many examples with associated easiness of use have been developed, even for other applications, but with high potentialities in this field. Cao and colleagues [241] have recently developed a colorimetric toehold switch biosensor integrated into a paper-based cell-free system, detecting down to aM in presence of target trigger RNA [194][195][196][197][198] diving PAM fluorometer -User friendly -Max 50 m -Very close to ( < 5 mm) [ 95 , 184 , 199 , 200 ] Respirometry system CISME device Net oxygen production in light vs oxygen consumption in dark -Use pH to estimate DIC variations -Specific software and instruments needed [106] Fluorescence variations analyses Fluorescence Imaging System (FluorIS) for recruitment ...
Biosensor technology represents a novel tool with several areas of application, such as biomedical and physicochemical ones. In this review, we considered this technology's application to physiological analyses in the area of biological response to climate change and environmental monitoring, with particular attention to the coral reefs. For their peculiar biology and sensitivity, coral reefs are considered nowadays as one of the most endangered marine ecosystems. Because of their natural and economical importance, analytical methods for evaluating the reef's health status are highly required to improve their protection. Several techniques based on different approaches are applied to coral reef research, mostly represented by remote surveys, in situ morphological observations, and laboratory-bound approaches. Only lately, some physiological in situ techniques have been proposed. The development of de-centralized biosensors could represent a terrific enhancement towards a real-time comprehension of coral reef health, especially in those areas that are scarcely accessible and/or with a low amount of sample to test.
Here we provide a detailed discussion about morphological and physiological aspects of the coral reef in situ analyses, providing the readers a critical overview of the advantages and limitations of current methodologies for coral reef monitoring. The desirable role of biosensors along the critical field of coral reefs’ assessment is highlighted and analyzed as a potential scenario for overcoming current limitations in climate change and local anthropogenic stressors monitoring.
... Generally, ZD declines to approximately 30 to 50% of the highest annual value due to the higher temperature and solar radiation intensity in summer (Stimson 1997, Fagoo nee et al. 1999, Venn et al. 2008, Xu et al. 2018. ZD and chl a are commonly used as photosynthesis indicators since they describe the ability of corals to capture light (Fitt et al. 2000, Harithsa et al. 2005, and decreases in ZD and/or chl a are accompanied by a net decrease in photosynthesis rate (Lombardi et al. 2000). For corals to remain healthy, they require sufficient energy to support growth, metabolism and reproduction (Ro drigues & Grottoli 2007). ...
Coral bleaching events are increasing in frequency and severity worldwide. From the perspective of energy supply, a decrease in symbiotic zooxanthellae density (ZD) during bleaching leads to a reduction in the amount of energy provided by photosynthesis to the coral host. However, there are still many unknowns about how corals maintain the stability of their energy supply when zooxanthellae decrease. In this study, 89 coral samples, including the relatively stress-tolerant massive Favia palauensis and Porites lutea and the relatively vulnerable branching Acropora millepora and Pocillopora damicornis , were collected from the Xisha Islands in the South China Sea in spring and summer 2020. The physiological parameters ZD, chl a , tissue biomass and lipid content were measured. The δ ¹³ C compositions of zooxanthellae and hosts were analyzed to explore the changes in trophic status in summer. Results show that the ZDs of A. millepora , P. damicornis , F. palauensis and P. lutea significantly decreased by 32, 29, 22 and 22%, respectively, in summer. P. lutea and F. palauensis maintained metabolic energy requirements depending largely on heterotrophy. A. millepora and P. damicornis were more dependent on consuming their own lipids. Our study shows that there are intergeneric differences in the energy maintenance mechanisms used to cope with decreases in ZD. We suggest that the higher heterotrophic ability of F. palauensis and P. lutea renders their trophic status more plastic than that of A. millepora and P. damicornis . This characteristic may potentially affect their bleaching resilience.
... The SCUBA-based FRR fluorometry was developed by Gorbunov et al for measuring chlorophyll fluorescence from PSII reaction centers in corals, sea grasses, macroalgae, and algal turfs. FRR fluorometry has been also used to monitor coral physiology during bleaching events and their later recovery (Lombardi et al., 2000;Lesser and Gorbunov, 2001). Although nutrient availability (as nitrogen or iron) and sunlight irradiance were already recognized as the main factors directly affecting photosynthesis in the aquatic ecosystem (Falkowski and Kolber, 1995;Behrenfeld and Kolber, 1999), the use of FRR fluorometry enabled more direct measurements of nutrient limitation effects on photosynthetic efficiency of corals. ...
Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency of massive bleaching events in the tropics is highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic stressors such as nutrient loading, increased turbidity, and coastal development. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to the entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights into metabolic performance under more complex and temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) in situ, and their role in indicating the health status of colonies and communities. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.
... The diving-PAM (D-PAM) and SCUBA-based FRRf are a portable fluorometer that can be used to take in situ point measurement using fibreoptics of 2 and 5.5 mm in diameter. Data can be collected directly from organisms in a mangrove forest or underwater during scuba diving (Lombardi et al., 2000;Jones and Hoegh-Guldberg, 2001;Gorbunov et al., 2001;Louis et al., 2016). Fluorometers like the Maxi PAM, 3D PAM and Imaging PAM provides the full image or 3D image of photosynthetic activities across a specimen's surface (Aldea et al., 2006;Ryan et al., 2011;Leal et al., 2015). ...
Chlorophyll a fluorescence is increasingly being used as a rapid, non-invasive, sensitive and convenient indicator of photosynthetic performance in marine autotrophs. This review presents the methodology, applications and limitations of chlorophyll fluorescence in marine studies. The various chlorophyll fluorescence tools such as Pulse-Amplitude-Modulated (PAM) and Fast Repetition Rate (FRR) fluorometry used in marine scientific studies are discussed. Various commonly employed chlorophyll fluorescence parameters are elaborated. The application of chlorophyll fluorescence in measuring natural variations, stress, stress tolerance and acclimation/adaptation to changing environment in primary producers such as microalgae, macroalgae, seagrasses and mangroves, and marine symbiotic invertebrates, namely symbiotic sponges, hard corals and sea anemones, kleptoplastic sea slugs and giant clams is critically assessed. Stressors include environmental, biological, physical and chemical ones. The strengths, limitations and future perspectives of the use of chlorophyll fluorescence technique as an assessment tool in symbiotic marine organisms and seaplants are discussed.
... Although many studies still involve the removal of specimens to adjacent laboratories to quantify symbiont densities or to run photosynthesis/respiration (P/R) incubations (Brown et al. 2000), submersible diving pulse-amplitude-modulated (PAM) fluorometers have been used (Ralph et al. 1999;Warner et al. 1999;Fitt et al. 2001) for in situ measurement of PSII before, during and after bleaching events. Lombardi et al. (2000) used a fast repetition rate fluorometer to show variability in fluorescence yields from corals at different stages of bleaching or recovery. The PAM fluorometer is capable of detecting the photoinhibition processes of the algal symbiont within the coral host that lead to widespread coral bleaching. ...
Widespread coral bleaching events are becoming more frequent and have occurred across all coral reef ecosystems throughout the tropical oceans. As the oceans continue to warm in the next few decades, the severity and frequency of coral bleaching is likely to continue to increase. Monitoring approaches to document the impacts of coral bleaching range from satellites to detect sea surface temperature anomalies and remote sensing imagery, aerial observations across wide spatial scales, to in-water detailed surveys of the coral reef community response. In this chapter, we outline the current approaches that have been employed by coral reef researchers to highlight the importance of consistent, comparable observations in order to synthesise the global impacts of coral bleaching for coral reef communities.
... fast-repetition-rate (FRR) fluorometers are capable of detecting total fluorescence of cell populations in vitro or in hospite [10,11]. Extracted chl a pigment has also been extensively studied [4,5]. ...
The partnership between coral and its algal symbionts, Symbiodinium, is crucial to the global environment. Yet, the regulatory process within the photosynthetic machinery of Symbiodinium is still not clearly understood. Here, we studied the influence of light stress from focused red and blue lasers on single Symbiodinium cells. Fluorescence signals were measured to show cell response. Increasing the incident laser power or the exposure time resulted in an increase followed by a decline in fluorescence intensity. The trend of fluorescence intensity changes was associated with mechanisms of light use efficiency, non-photochemical quenching, photoinhibition, and repair of the cell. Our study provides new approaches to studying the photobiology and physiology of Symbiodinium cells.
... The pulse amplitude modulated fluorescence technique used widely can measure steady fluorescence parameters in situ, because the measurement light is modulated by the pulse, and the modulated fluorescence is demodulated by using the lock-in amplifier [5,6] . The fast repetition rate (FRR) fluorescence technique is very efficient in measuring variable fluorescence parameters [7,8] . Due to using the direct-current amplifier, it is usually used in dark. ...
... Light and water temperature have been reported as the most important factors affecting the physiology of zooxanthellae (Lombardi et al., 2000;Gorbunov et al., 2001;Glynn et al., 2001;Warner et al., 2002). These parameters are certainly coresponsible for the temporal variations of the zooxanthellae in shallow and coastal waters in the studied area, although light seems to have the most influence. ...
A B S T R A C T The seasonal dynamics of cell density and photosynthetic pigment contents of the zooxanthellae hosted by Montastrea cavernosa were investigated on coastal reefs off Picãozinho (06 o 42'05 " /07 o 07'30 " S and 34 o 48'37 " /34 o 50'00 " W), Northeast Brazil between September 1999 and 2000. A distinct pattern of these parameters was found: cell numbers were greater during the rainy season (autumn/winter) while photosynthetic pigments were greater during the dry season (summer). Both parameters showed drastic reductions during heavy rains (June and July 1999). We speculate that this pattern is largely influenced by the rain cycles which, owing to their magnitude and frequency, affect the water clarity and the seasonal physiological condition of the cells. R E S U M O A dinâmica sazonal na densidade de células e na concentração de pigmentos fotossintetizantes das zooxantelas de Montastrea cavernosa foram analisados no período setembro/1999 a setembro/2000 nos Recifes do Picãozinho (06 o 42'05 " /07 o 07'30 " S e 34 o 48'37 " /34 o 50'00 " W), Nordeste do Brasil. Verificou-se que existe um padrão distinto entre estes parâmetros, com maior quantidade de células no período chuvoso e maior concentração de pigmentos fotossintetizantes na época de estiagem. Ambos os parâmetros apresentaram, no entanto, uma nítida redução em seus valores nos meses de maiores índices pluviométricos (junho e julho /1999). Especulamos que tal fato deve estar relacionado com o regime de chuvas que pode variar em magnitude e freqüência, afetando a qualidade ótica da água e o estado fisiológico das células.
... Light and water temperature have been reported as the most important factors affecting the physiology of zooxanthellae (Lombardi et al., 2000;Gorbunov et al., 2001;Glynn et al., 2001;Warner et al., 2002). These parameters are certainly coresponsible for the temporal variations of the zooxanthellae in shallow and coastal waters in the studied area, although light seems to have the most influence. ...
... Previous work has shown that in some cases corals that display a greater reduction in in situ DF/F 9 m are more susceptible to natural bleaching (Lombardi et al. 2000). An important result of this current work is the link between in situ maximum excitation pressure over PSII and the potential for thermally enhanced photoinhibition related to coral bleaching. ...
The photobiology and distribution of dinoflagellates in the genus Symbiodinium was investigated for eight common reef coral species over a depth range of 1-25 m on a coral reef in Belize. The genetic identification of symbionts using polymerase chain reaction-denaturing gradient electrophoresis of the internal transcribed spacer 2 region revealed marked differences in host specificity and depth zonation for certain symbiont types. Each host taxon was found to associate with a limited subset of symbionts that exist in the region. Intraspecific variation was greatest at the shallower sites (1-8 m), where as many as five distinctive symbionts were distributed among a single host population (e.g., Montastraea faveolata). At depth (15-25 m), variation from colony to colony was minimal, where one algal type associated with most or all the colonies of a species. The maximal photochemical efficiency and light-acclimated efficiency of photosystem II (PSII) were determined by active chlorophyll fluorescence and used to assess potential differences in photosynthetic potential. Under normal ambient conditions, little or no physiological differences were noted among different symbionts occurring in the same species of coral at a particular depth, yet interspecific differences in PSII efficiency were noted between coral species at the same depth. Short-term bleaching experiments showed that symbionts B1 and C7 within M. faveolata experienced a higher degree of thermally induced photoinhibition relative to A4a symbionts in Porites astreoides. The differential patterns of PSII inactivation observed within M. faveolata could be explained by the presence of different symbiont populations within this coral. Differences in in situ maximum excitation pressure on PSII between symbionts within some corals may provide a predictive measure of how different species of coral or individual colonies with different symbionts would respond to natural thermal stress events.
... Bleached corals show decreased algal densities, chl a and host tissue biomass (Porter et al. 1989;Szmant and Gassman 1990;Fitt et al. 1993;Allison et al. 1996;Suzuki et al. 2000Suzuki et al. , 2003Grottoli et al. 2004) impaired photosynthesis (Tchernov et al. 2004), a net decrease in photosynthesis (Warner et al. 1996;Lesser 1997;Lombardi et al. 2000) and lipid content (Grottoli et al. 2004;Yamashiro et al. 2005), and possibly lower heterotrophy, resulting in the loss of some important nutrition. FA synthesis in corals is directly coupled with photosynthesis (Oku et al. 2003); impaired photosynthesis during bleaching may affect FA metabolism, in particular the FA biosynthetic pathways, resulting in changes in FA composition and reduced lipid production. ...
Under bleaching conditions, corals lose their symbiotic zooxanthellae, and thus, the ability to synthesize fatty acids (FAs)
from photosynthetically derived carbon. This study investigated the lipid content and FA composition in healthy and bleached
corals from the Odo reef flat in Okinawa, southern Japan, following a bleaching event. It was hypothesized that the FA composition
and abundance would change as algae are lost or die, and possibly microbial abundance would increase in corals as a consequence
of bleaching. The lipid content and FA composition of three healthy coral species (Pavona frondifera, Acropora pulchra, and Goniastrea aspera) and of partially bleached and completely bleached colonies of P. frondifera were examined. The FA composition did not differ among healthy corals, but differed significantly among healthy, partially
bleached, and completely bleached specimens of P. frondifera. Completely bleached corals contained significantly lower lipid and total FA content, as well as lower relative amounts of
polyunsaturated FAs and higher relative amounts of saturated FAs, than healthy and partially bleached corals. Furthermore,
there was a significantly higher relative concentration of monounsaturated FAs and odd-numbered branched FAs in completely
bleached corals, indicating an increase in bacterial colonization in the bleached corals.
... Although many studies still involve the removal of specimens to adjacent laboratories (Brown et al. 2000), submersible tools do exist (Ralph et al. 1999;Warner et al. 1999;Fitt et al. 2001) for in situ measurement. Lombardi et al. (2000) used a fast repetition rate fluorometer to show variance in fluorescence yields from corals at different stages of bleaching, or recovery, while Hochberg et al. (2005) showed that a good estimate can be made of pigment densities using detailed recordings of optical reflectance spectra. ...
Detecting and monitoring coral bleaching is considered across three broad spatial scales: remote sensing; field studies; and
individual coral colonies and polyps. Remote sensing observations have limitations, although aerial photography offers sufficient
resolution for detecting and quantifying bleaching. Much lower resolution SST anomalies have also proved valuable as short-term
predictors of bleaching and in post hoc bleaching likelihood indicators for un-surveyed areas. Field based observations offer
reliability at the expense of reduced spatial coverage. Nested sampling may allow for generalised observations across all
reef zones, while allowing for more accurate quantification at fixed locations. Methods should be devised to facilitate comparison
with other monitoring; and must include measures of mortality, recovery and recruitment over time. At the scale of individual
colonies a broad array of techniques are available for in situ and field laboratory observations, strengthening our understanding
of underlying mechanisms and supporting better predictive modelling of future impacts.
... Since fluorescence intensity varies with incident irradiance, regressions computed using R may be sensitive to fluctuating light conditions. Chlorophyll fluorescence near 685 nm by zooxanthellae is well documented and is the basis for PAM and FRR fluorometric methods of assessing photosystem II status (Beer et al. 1998;Lombardi et al. 2000;Gorbunov et al. 2001). This type of fluorescence is certainly present in all of the R's in our data set. ...
The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c
2, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c
2. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes.
... Chlorophyll ¯uorescence measurement is a very powerful and useful tool for monitoring the physiology of symbiotic dino¯agellates within scleractinians. The two techniques currently available for measuring changes in chlorophyll ¯uorescence under dark-and light-acclimated conditions are pulse amplitude modulation (PAM) ¯uorometry and fast repetition rate (FRR) ¯uorometry (Warner et al. 1996; Lombardi et al. 2000). For this discussion, we will focus primarily on PAM ¯uorometry, since it represents instrumentation which is more readily available to most laboratories. ...
'It should be clear that the upper temperature limit for life cannot be accurately defined' (Schmidt-Nielsen 1996). The thermal physiology of zooxanthellate reef corals is reviewed in this paper in the context of organismal and biochemical responses occurring during coral bleaching, with emphasis on methods of detection and interpretation of animal and algal symbiont stress. Coral bleaching, as presently defined in the literature, is a highly subjective term used to describe a variety of conditions pertaining to low symbiont densities in the coral-algal complex, including response to thermal stress. Three general types of high-temperature bleaching are defined: physiological bleaching, which may or may not include higher-than-normal temperature responses; algal-stress bleaching, involving dysfunction of symbiotic algae at high light and/or high temperatures; and animal-stress bleaching, where coral cells containing symbiotic algae are shed from the gastrodermal layer of cells. Since none of these methods of bleaching is mutually exclusive, a combination of intrusive and non-intrusive techniques is necessary to determine which mechanisms of symbiont loss are occurring. While quantification of symbiont densities, algal pigments, and coral tissue biomass provide unambiguous evidence of bleaching severity, measurements of physiological and biochemical degradation offer additional correlative evidence of temperature stress. Pulse-amplitude-modulated (PAM) fluorometry has emerged as an easy and relatively inexpensive non-invasive technique for monitoring symbiotic algal function both in situ and in the laboratory, when proper assumptions and interpretations are made. The roles of global warming, water quality, acclimation/adaptation processes, and relation to coral disease and reef heterogeneity are also discussed. A thorough understanding of the organismal responses occurring during bleaching will help explain changes in coral populations and in the coral reef community, and perhaps assist in predicting the future of reef corals and coral reefs during the next century of global climate change.
... Among the benefits of synchronous-scan-fluorescence spectroscopy are its enhanced selectivity and its high sensitivity to a wide array of analytes, and no reagents are required in the case of algal cells. The aim of this paper is not to investigate the mechanism of algae photosynthesis and their photosystems which require specific techniques such as pulse amplitude-modulated (PAM) fluorometry (Jones et al., 1999), and fast repetition rate (FRR) fluorometry (Lombardi et al., 2000). In this study, synchronous-scan spectrofluorometry was applied to C. vulgaris cells for analytical applications and in order to assess the toxicity of heavy metals and herbicides in water. ...
Synchronous-scan spectrofluorometry was applied to Chlorella vulgaris cells to assess the toxicity of heavy metals and herbicides in water. Simultaneous scan of both the excitation and emission spectra was done at a constant wavelength difference Δλ (20–140 nm) between the emission and excitation wavelengths in the range of 420–700 nm emission, where a peak of fluorescence was observed. Its position depends on Δλ. Fluorescence measurements were conducted with algal cells in suspension in water and immobilized in a translucent silica matrix. The influence of toxic chemicals was tested with cadmium as a heavy metal and with atrazine, diuron, DNOC and paraquat as herbicides. The toxic effect of those chemicals mainly results in a quenching of algal cells fluorescence by reducing their photosynthetic activity.
... In the present study, during a bleaching event, the ETR max for zooxanthellae in a bleached section of the colony is reduced to approximately 16% that of healthy ones. Similar observations are reported elsewhere by Warner et al. (1999) and Lombardi et al. (2000), who showed that bleached areas of a coral colony have lower ETRs through PSII than visibly non-bleached colonies. Ostreobium sp. ...
The photoacclimation of endolithic algae ( of the genus Ostreobium) inhabiting the skeleton of the Mediterranean coral Oculina patagonica during a bleaching event was examined. Pulse amplitude modulated (PAM) chlorophyll fluorescence techniques in situ were used to assess the photosynthetic efficiency of endolithic algae in the coral skeleton and the symbiotic dinoflagellates (zooxanthellae) in the coral tissue. Relative photosynthetic electron transport rates (ETRs) of the endolithic algae under bleached areas of the colony were significantly higher than those of endolithic algae from a healthy section of the colony and those of zooxanthellae isolated from the same section. Endolithic algae under healthy parts of the colony demonstrated an ETRmax of 16.5% that of zooxanthellae from tissue in the same section whereas endolithic algae under bleached sections showed ETRmax values that were 39% of those found for healthy zooxanthellae. The study demonstrates that endolithic algae undergo photoacclimation with increased irradiance reaching the skeleton. As PAM fluorometry has become a major tool for assessing levels of stress and bleaching in corals, the importance of considering the contribution of the endolithic algae to the overall chlorophyll fluorescence measured is highlighted.
... Previous studies of corals exposed to increased temperature stress have indicated that symbiotic dinoflagellates in bleached regions of a colony exhibit reduced photosynthetic activity for up to one year after a bleaching event (Lombardi et al. 2000). In the present study, photochemical efficiency, density of symbiotic dinoflagellates and concentration of photosynthetic pigments of corals exposed to a 6 h treatment at 15°C had recovered completely over the three month period. ...
Coral bleaching events have become more frequent and widespread, largely due to elevated sea surface temperatures. Global climate change could lead to increased variability of sea surface temperatures, through influences on climate systems, e.g. El Nino Southern Oscillation (ENSO). Field observations in 1999, following a strong ENSO, revealed that corals bleached in winter after unusually cold weather. To explore the basis for these observations, the photosynthetic responses of the coral species Montipora digitata Studer were investigated in a series of temperature and light experiments. Small replicate coral colonies were exposed to ecologically relevant lower temperatures for varying durations and under light regimes that ranged from darkness to full sunlight. Photosynthetic efficiency was analyzed using a pulse amplitude modulated (PAM) fluorometer (F-0, F-m, F-v/F-m), and chlorophyll a (chl a) content and symbiotic dinoflagellate density were analyzed with spectrophotometry and microscopy, respectively. Cold temperature stress had a negative impact on M digitata colonies indicated by decreased photosynthetic efficiency (F-v/F-m), loss of symbiotic dinoflagellates and changes in photosynthetic pigment concentrations. Corals in higher light regimes were more susceptible to cold temperature stress, Moderate cold stress resulted in photoacclimatory responses, but severe cold stress resulted in photodamage, bleaching and increased mortality. Responses to cold temperature stress of M digitata appeared similar to that observed in corals exposed to warmer than normal temperatures, suggesting a common mechanism. The results of this study suggest that corals and coral reefs may also be impacted by exposure to cold as well as warm temperature extremes as climate change occurs.
... In contrast, fluorescence may indicate photodamage even if the tissue appears visually healthy. Fluorescence yield may or may not return to baseline after short-term damage (present study; Philipp and Fabricius, 2003;Weber et al., 2006), and reduced yields may persist for up to a year following bleaching events ( Lombardi et al., 2000). While decreased fluorescence yield is a common stress response, few studies have examined the energetic consequences of such changes. ...
This study used non-invasive pulse-amplitude modulated (PAM) fluorometry to measure the maximum fluorescence yield (F(v)/F(m)) of two Hawaiian scleractinian coral species exposed to short-term sedimentation stress. Beach sand or harbor mud was applied to coral fragments in a flow-through aquarium system for 0-45 h, and changes in F(v)/F(m) were measured as a function of sediment type and length of exposure. Corals were monitored for up to 90 h to document recovery after sediment removal. Sediment deposition significantly decreased F(v)/F(m) in both species and was a function of sediment type and time. Corals that received sediment for 30 h or more had the greatest reduction in yield and exhibited little recovery over the course of the experiment. Harbor mud caused a greater reduction in Porites lobata yield than beach sand, whereas both sediment types had equally deleterious effects on Montipora capitata. Colony morphology and sediment type were important factors in determining yield reduction--P. lobata minimized damage from coarse sand grains by passive sediment rejection or accumulation in depressions in the skeleton, and fluorescence yield decreased most in corals exposed to sticky harbor mud or in colonies with flattened morphologies. Species-specific differences could not be tested due to differences in colony morphology and surface area.
Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency and severity of massive bleaching events in the tropics are highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic issues such as nutrient loading, increased turbidity, and coastal development. The changes in coral metabolism under local or global stress conditions is studied largely through laboratory manipulation and field observations. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to an entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights to metabolic performance under more complex temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of current experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) and their role in indicating the health status of colonies and communities. The state of the art of in situ techniques for experimental and monitoring purposes is explored. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.
Chlorophyll fluorescence, a method for noninvasive analysis of the photosynthetic activity in plants and algae, is a commonly used technique in physiology and ecophysiology. In recent years it has developed as a key technique to analyze the regulatory mechanisms of the energy conversion within photosystem II, and is also used as an easy-to-handle indicator of the responses of photosynthetic organisms to environmental changes. The construction of waterproofed instruments for usage in the field facilitates investigations also in the aquatic ecosystems under natural conditions. Although instruments are generally easy to handle it is necessary to understand the theoretical background of this technique and methodology to avoid technical pitfalls as well as misinterpretation of data achieved. Though fluorescence parameters can give hints to the performance of primary production, they are not sufficient for a proper determination. This chapter explains the theoretical and technical background especially for newcomers, explains the most important fluorescence parameters, and introduces and compares the most commonly used instruments that are now available on the market. Moreover, methodological tips for proper measurements are described because operating guidelines of manufacturers are usually insufficient or according to the kind of the measuring protocol special instruments are favored.
A B S T R A C T The seasonal dynamics of cell density and photosynthetic pigment contents of the zooxanthellae hosted by Montastrea cavernosa were investigated on coastal reefs off Picãozinho (06 o 42'05 " /07 o 07'30 " S and 34 o 48'37 " /34 o 50'00 " W), Northeast Brazil between September 1999 and 2000. A distinct pattern of these parameters was found: cell numbers were greater during the rainy season (autumn/winter) while photosynthetic pigments were greater during the dry season (summer). Both parameters showed drastic reductions during heavy rains (June and July 1999). We speculate that this pattern is largely influenced by the rain cycles which, owing to their magnitude and frequency, affect the water clarity and the seasonal physiological condition of the cells. R E S U M O A dinâmica sazonal na densidade de células e na concentração de pigmentos fotossintetizantes das zooxantelas de Montastrea cavernosa foram analisados no período setembro/1999 a setembro/2000 nos Recifes do Picãozinho (06 o 42'05 " /07 o 07'30 " S e 34 o 48'37 " /34 o 50'00 " W), Nordeste do Brasil. Verificou-se que existe um padrão distinto entre estes parâmetros, com maior quantidade de células no período chuvoso e maior concentração de pigmentos fotossintetizantes na época de estiagem. Ambos os parâmetros apresentaram, no entanto, uma nítida redução em seus valores nos meses de maiores índices pluviométricos (junho e julho /1999). Especulamos que tal fato deve estar relacionado com o regime de chuvas que pode variar em magnitude e freqüência, afetando a qualidade ótica da água e o estado fisiológico das células.
The newest approach in the saturation fluorimetry of photosynthetic organisms by the example of phytoplankton was developed. The theoretical model and the inverse problem of the saturation fluorimetry are discussed. The results of evaluation of molecular photophysical parameters of alga Chlorella pyrenoidosa under various stress factors, such as presence of DCMU and Cu2+ ions are presented. The correlation between theese parameters and the parameters obtained using Fluorescence Induction and Relaxation technique is discussed.
Since its introduction in the early 1960s, in vivo chlorophyll fluorescence has been used as an index of photosynthetic biomass
in marine ecosystems. In the late 1980s, however, active fluorometric techniques, originally based on the pump and probe method,
were used to derive estimates of photosynthetic electron transport, the overall quantum efficiency of photosynthetic energy
conversion, and the effective cross section of Photosystem II. It was quickly realized that nutrient limitation, but not acclimation
to light or temperature, had a profound influence on photosynthetic energy conversion efficiency (reported as, e.g., Fv/Fm). Subsequently, variable fluorescence techniques were employed to assess physiological control of oceanic photosynthesis
by nutrients that potentially limit photosynthetic electron transport. The pump and probe technique was subsequently supplanted
by a fast repetition rate (FRR) fluorescence method, which greatly improved the precision and efficiency of variable fluorescence
measurements at sea. The FRR method has revealed how the availability of iron, fixed inorganic nitrogen, and phosphate control
photosynthetic electron transport rates throughout the world oceans. The technique has been further applied to corals, seagrasses,
single cells of free-living marine phytoplankton, and anoxygenic aerobic photosynthetic bacteria. Variable fluorescence data
reveal extraordinary physiological plasticity of the photosynthetic apparatus in the genetically diverse group of organisms
that comprise the primary producers in contemporary oceanic ecosystems.
The novel algorithms of evaluating four molecular photophysical parameters of the photosynthetic apparatus of photosynthetic organisms (by the example of phytoplankton) were developed. These algorithms open up new possibilities for using photosynthetic organisms as natural bioindicators of the state of ecosystem and particularly for using phytoplankton as an indicator of presence of vari-ous pollutants in natural waters. Proposed approaches were tested during evaluation of the photo-physical parameters of alga Chlorella pyrenoidosa under various stress factors, including presence of DMCU and Cu 2+ ions.
The effects of seawater temperature on the degree of success of self-fertilization versus cross-fertilization and on embryogenesis were investigated in the scleractinian coral Diploria strigosa (Dana 1846). Gametes from nine colonies were collected from the Flower Garden Banks reefs, a set of coral reefs in the northern Gulf of Mexico, ~110 nm offshore from Texas, United States. Gametes from the coral colonies were combined in all possible combinations and placed in 30, 31, and 32C water baths on successive nights, respectively. Each cross, whether selfed or out-crossed, and each temperature treatment, was replicated twice. A high frequency of successful self- and cross-fertilization was observed at all temperature treatments and in both blocks. Higher temperatures, however, commonly produced numerous developmental aberrations during embryogenesis of the larvae. Thus, although fertilization rates can remain high under high temperature conditions, if temperatures remain high for several days, embryonic development and larval viability may be expected to decrease dramatically. We propose that the success of coral larval development may be diminished in areas where abnormally high sea surface temperatures occur during the spawning season. We also propose that highly successful selfing may enhance the abundance of locally adapted genotypes, which in turn may be advantageous where reefs, such as the Flower Garden Banks, are relatively geographically isolated.
In this paper, I review data on the magnitude and extent of reef coral bleaching events and consider modern hypotheses on the mechanisms of this natural phenomenon and experimental data lying at their basis. Four possible mechanisms of color loss by hermatypic corals have been confirmed experimentally: bacterial infection, change of zooxanthellae type in the polyps to improve the heat resistance of the photosynthetic function of coral to elevated seawater temperature, intoxication of zooxanthellae by animal metabolic wastes at high temperature and light levels, and thermal and photodestruction of the animal and algal cells. The heating effect of photosynthetic active radiation on the zooxanthellar cells in coral polyps was verified theoretically. The calculations showed that in the natural environment, the additional light-induced heating of zooxanthellae is not above 0.01C and that it cannot cause disruption of the animal and zooxanthellae symbiosis.
A newly developed fluorescence measuring system is employed for the recording of chlorophyll fluorescence induction kinetics (Kautsky-effect) and for the continuous determination of the photochemical and non-photochemical components of fluorescence quenching. The measuring system, which is based on a pulse modulation principle, selectively monitors the fluorescence yield of a weak measuring beam and is not affected even by extremely high intensities of actinic light. By repetitive application of short light pulses of saturating intensity, the fluorescence yield at complete suppression of photochemical quenching is repetitively recorded, allowing the determination of continuous plots of photochemical quenching and non-photochemical quenching. Such plots are compared with the time courses of variable fluorescence at different intensities of actinic illumination. The differences between the observed kinetics are discussed. It is shown that the modulation fluorometer, in combination with the application of saturating light pulses, provides essential information beyond that obtained with conventional chlorophyll fluorometers.
Chlorophyll fluorescence was used to assess the iu situ photosynthesis of a range of reef-dwelling endosymbionts. Such non-intrusive in situ measurements became possible after the recent development of a submersible pulse modulated fluorometer (DIVING-PAM, Walt, Germany). Several corals, a clam (Tridacna maxima) and an anemone (Heteractis rip.) all showed strong chlorophyll a fluorescence signals originating from the dinoflagellate endosymbionts. Quenching analysis by the saturation pulse method revealed high quantum yields and Light response curves characteristic of physiologically healthy sun plants. Rapid light curves (RLC) were applied to assess the light saturation behaviour of the different organisms in their rapidly changing natural environment. The 3 corals (Acropora aspera, Goniastrea sp. and Porites sp), the clam T. maxima, and the anemone Heteractis sp. all showed high photosynthetic activity. The corals had a maximum electron transport rate of 180 to 270 mu mol electrons m(-2) s(-1), the Heteractis sp, displayed a maximum rate of approximately 120 mu mol electrons m(-2) s(-1), whilst the T. maxima showed no saturation up to 1900 mu mol quanta m(-2) s(-1), where a rate of 325 mu mol electrons m(-2) s(-1) was observed. Three species of corals showed varying degrees of an apparent mid-day depression, occurring during the summer peak irradiance at low tide. Because quantum efficiency rapidly recovered during the afternoon period, when the irradiance levels decreased again, it is concluded from these preliminary investigations that the depression resulted mainly from down-regulation of photosystem II. Depth did not appear to influence the RLCs of A. aspera growing at 2, 5 and 10 m. Coral morphology influenced the apparent electron transport rate at different locations within a single colony.
Diurnal patterns of photoinhibition have been identified in seven species of shallow water reef corals from the Andaman Sea,
off the west coast of Thailand, using pulse amplitude fluorometry. Photochemical efficiency (Fv/Fm) and quantum yield (ΔF/Fm∑) of symbiotic dinoflagellates within the corals declined after dawn to reach a minimum between midday and early afternoon,
recovering to former dawn levels by early evening. Parallel studies on the xanthophylls diadinoxanthin (Dn) and diatoxanthin
(Dt), and their inter-conversion, also revealed a strong diurnal pattern as well as inverse correlations between the xanthophyll
ratio Dt/(Dn+Dt) and Fv/Fm and ΔF/Fm′. These findings suggest a photoprotective function for these pigments.
Elevated temperatures and solar ultraviolet (UV) radiation have been implicated as recent causes for the loss of symbiotic
algae (i.e., bleaching) in corals and other invertebrates with photoautotrophic symbionts. One hypothesized mechanism of coral
bleaching involves the production of reduced oxygen intermediates, or toxic oxygen, in the dinoflagellate symbionts and host
tissues that subsequently causes cellular damage and expulsion of symbionts. Measurements of photosynthesis in the Caribbean
coral Agaricia tenuifolia, taken during temperature-induced stress and exposure to full solar radiation, showed a decrease in photosynthetic performance
followed by bleaching. Exposure of corals to exogenous antioxidants that scavenge reactive oxygen species during temperature-induced
stress improves maximum photosynthetic capacity to rates indistinguishable from corals measured at the ambient temperature
of their site of collection. Additionally, these antioxidants prevent the coral from “ bleaching ” and affect the mechanism
of symbiont loss from the coral host. These observations confirm a role for oxidative stress, whether caused by elevated temperatures
or exposure to UV radiation, in the bleaching phenomenon.
Cyanobacteria are ecologically important photosynthetic prokaryotes that also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanobacteria benefit from real-time information on photosynthesis and acclimation. Monitoring in vivo chlorophyll fluorescence can provide noninvasive measures of photosynthetic physiology in a wide range of cyanobacteria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of key structural and functional properties of cyanobacteria. These include significant fluorescence emission from the light-harvesting phycobiliproteins; large and rapid changes in fluorescence yield (state transitions) which depend on metabolic and environmental conditions; and flexible, overlapping respiratory and photosynthetic electron transport chains. The fluorescence parameters FV/FM, FV'/FM',qp,qN, NPQ, and phiPS II were originally developed to extract information from the fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and used to extract biologically useful information from cyanobacterial in vivo chlorophyll fluorescence signals. We describe how the pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes. The size of the change in fluorescence yield during dark-to-light transitions can provide information on respiration and the iron status of the cyanobacteria. Finally, fluorescence parameters can be used to estimate the electron transport rate at the acclimated growth light intensity.
Elevated temperature (28-34 degrees C) has been hypothesized as the primary cause of the loss of algal endosymbionts in coral reef-associated invertebrates, a phenomenon observed on a world-wide scale over the last decade. In past studies of this "bleaching" phenomenon, there has been an underlying assumption that temperature adversely affects the animal hosts, the algae thereby being relegated to a more passive role. Because photosynthesis is a sensitive indicator of thermal stress in plants and has a central role in the nutrition of symbiotic invertebrates, we have tested the hypothesis that elevated temperature adversely affects photosynthesis in the symbiotic dinoflagellate Symbiodinium microadriaticum. The results, based on analyses of light-mediated O2 evolution and in vivo fluorescence, indicate that photosynthesis is impaired at temperatures above 30 degrees C and ceases completely at 34-36 degrees C. These observations are discussed in the context of possible mechanisms that may function in the disassociation of algal-invertebrate symbioses in response to elevated temperature.
Coral reef bleaching, the temporary or permanent loss of photosynthetic microalgae (zooxanthellae) and/or their pigments by a variety of reef taxa, is a stress response usually associated with anthropogenic and natural disturbances. Degrees of bleaching, within and among coral colonies and across reef communities, are highly variable and difficult to quantify, thus complicating comparisons of different bleaching events. Small-scale bleaching events can often be correlated with specific disturbances (e.g. extreme low/high temperatures, low/high solar irradiance, subaerial exposure, sedimentation, freshwater dilution, contaminants, and diseases), whereas large scale (mass) bleaching occurs over 100s to 1000s of km2, which is more difficult to explain. Debilitating effects of bleaching include reduced/no skeletal growth and reproductive activity, and a lowered capacity to shed sediments, resist invasion of competing species and diseases. Severe and prolonged bleaching can cause partial to total colony death, resulting in diminished reef growth, the transformation of reef-building communities to alternate, non-reef building community types, bioerosion and ultimately the disappearance of reef structures. Present evidence suggests that the leading factors responsible for large-scale coral reef bleaching are elevated sea temperatures and high solar irradiance (especially ultraviolet wavelenths), which may frequently act jointly.
Publisher Summary The aim of this chapter is to consider long-term ecological studies in the light of known effects of disturbances on coral reefs and to ask whether the effects of disturbances can be distinguished from long-term fluctuations on the reef, and also where other difficulties lie in assessment of pollution in the field. In addition, in an attempt to improve the understanding of the overall susceptibility of reef corals to marine pollution, an assessment is made of the responses of corals to stress and methods by which these responses have been monitored to date. The chapter deals with dealing with observations in the field, the laboratory assessment of pollutant effects, and incorporating a general discussion of the validity of generalizations made to date on the overall vulnerability of coral reefs to man-made disturbance. Although it is possible that any meaningful laboratory measurement of effects of stress in reef corals will involve a much more subtle approach than has been applied to date, the value of critical methods of evaluation of pollution in the field, such as those described here, should not be underestimated.
We describe the theory and practice of estimating photosynthetic rates from light-stimulated changes in the quantum yield of chlorophyll fluorescence. By means of a pump-and-probe fluorescence technique, where weak probe flashes are used to measure the change in the quantum yield of fluorescence induced by the strong pump flash, it is possible to derive the absolute absorption cross sections for photosystem 2, the quantum yield for photochemistry, and the maximum rate of photosynthetic electron transport at light saturation. In conjunction with a semiempirical biophysical model of photosynthesis, these param- eters can bc used to calculate the instantaneous rate of gross photosynthesis in situ under ambient irradiance. A profiling pump-and-probe fluorometer was constructed and interfaced with a CTD, and vertical profiles of variable fluorescence were obtained on four cruises in the northwest Atlantic Ocean. The derived photosynthetic rates were compared with concurrent estimates of production based on radiocarbon uptake. The correlation coefficient between the two estimates of primary production, nor- malized to Chl a, was 0.86; linear regression analysis yielded a slope of 1.06. There is a 3-4-fold range in the maximum change in the quantum yields of photochemistry and absorption cross-sections in natural phytoplankton communities. Uncertainties in the pump-and-probe-derived estimates of photosynthesis arc primarily due to temporal mismatches between instantaneous and time-integrated measures of pro- duction and in biological variability in the ratio of the number of PS2 reaction centers to total Chl a. Almost all measurements of phytoplankton photosynthesis in situ are based on the time- dependent incorporation of radiocarbon into particulate matter or on changes in concentra- tion of dissolved oxygen in the bulk fluid.
Benthic photoautotrophic organisms significantly contribute to the productivity of shallow tropical coastal ecosystems. However, measurements of photosynthetic light use and dissipation in benthic organisms are complicated by taxonomic diversity, spatial heterogeneity, natural variability in local nutrient, irradiance, and temperature regimes, as well as destructive sampling protocols. To help overcome these problems, we developed a SCUBA-based fast repetition rate (FRR) fluorometer for measurements of variable chlorophyll fluorescence in corals, sea grasses, macroalgae, and algal turfs. Photosynthetic light use and electron transport can be readily calculated from variable fluorescence kinetics. Using the SCUBA-based FRR fluorometer, changes in photosynthetic processes can be measured nondestructively in situ with high spatial and temporal resolution. Here we describe the instrument design and characteristics and present representative field results.
During the past decade, acute and chronic bleaching of tropical reef corals has occurred with in- creasing frequency and scale. Bleaching, i.e., the loss of pigment and the decrease in population density of sym- biotic dinoflagellates (zooxanthellae), is often correlated with an increase or decrease in sea surface temperature. Because little is known of the cellular events concomitant with thermal bleaching, we have investigated the mech- anism of release of zooxanthellae by the tropical sea ane- mone Aiptasia pulchella and the reef coral Pocillopora damicornis in response to cold and heat stress. Both spe- cies released intact host endoderm cells containing zoox- anthellae. The majority of the released host cells were viable, but they soon disintegrated in the seawater leaving behind isolated zooxanthellae. The detachment and re- lease of intact host cells suggests that thermal stress causes host cell adhesion dysfunction in these cnidarians. Knowledge of the cellular entity released by the host dur- ing bleaching provides insight into both the underlying release mechanism and the way in which natural envi- ronmental stresses evoke a bleaching response.
Photosynthesis can be described by target theory, At low photon flux densities, photosynthesis is a linear function of irradiance (I), The number of reaction centers (n), their effective absorption capture cross section {sigma}, and a quantum yield {phi}. As photosynthesis becomes increasingly light saturated, an increased fraction of reaction centers close. At light saturation the maximum photosynthetic rate is given as the product of the number of reaction centers (n) and their maximum electron transport rate (I/{tau}). Using active fluorometry it is possible to measure non-destructively and in real time the fraction of open or closed reaction centers under ambient irradiance conditions in situ, as well as {sigma} and {phi} {tau} can be readily, calculated from knowledge of the light saturation parameter, I{sub k} (which can be deduced by in situ by active fluorescence measurements) and {sigma}. We built a pump and probe fluorometer, which is interfaced with a CTD. The instrument measures the fluorescence yield of a weak probe flash preceding (f{sub 0}) and succeeding (f{sub 0}) a saturating pump flash. Profiles of the these fluorescence yields are used to derive the instantaneous rate of gross photosynthesis in natural phytoplankton communities without any incubation. Correlations with short-term simulated in situ radiocarbon measurements are extremely high. The average slope between photosynthesis derived from fluorescence and that measured by radiocarbon is 1.15 and corresponds to the average photosynthetic quotient. The intercept is about 15% of the maximum radiocarbon uptake and corresponds to the average net community respiration. Profiles of photosynthesis and sections showing the variability in its composite parameters reveal a significant effect of nutrient availability on biomass specific rates of photosynthesis in the ocean.
Coral reef bleaching, the temporary or permanent loss of photosynthetic microalgae (zooxanthellae) and/or their pigments by a variety of reef taxa, is a stress response usually associated with anthropogenic and natural disturbances. Degrees of bleaching, within and among coral colonies and across reef communities, are highly variable and difficult to quantify, thus complicating comparisons of different bleaching events. Small-scale bleaching events can often be correlated with specific disturbances (e.g. extreme low/high temperatures, low/high solar irradiance, subaerial exposure, sedimentation, freshwater dilution, contaminants, and diseases), whereas large scale (mass) bleaching occurs over 100s to 1000s of km2, which is more difficult to explain. Debilitating effects of bleaching include reduced/no skeletal growth and reproductive activity, and a lowered capacity to shed sediments, resist invasion of competing species and diseases. Severe and prolonged bleaching can cause partial to total colony death, resulting in diminished reef growth, the transformation of reef-building communities to alternate, non-reef building community types, bioerosion and ultimately the disappearance of reef structures. Present evidence suggests that the leading factors responsible for large-scale coral reef bleaching are elevated sea temperatures and high solar irradiance (especially ultraviolet wavelengths), which may frequently act jointly.
Bleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are known as zooxanthellae, and/or loss of algal pigments. The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, Agaricia lamarki, Agaricia agaricites and Siderastrea radians was examined by pulse-amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (30–36°C). Zooxanthellae within M. annularis and A. lamarki were found to be more sensitive to elevated temperature, virtually complete disruption of photosynthesis being noted during exposure to temperatures of 32 and 34°C. The photosynthetic efficiency of zooxanthellae within S. radians and A. agaricites decreased to a lesser extent. Differences in the loss of algal cells on an aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the non-invasive PAM technique with whole-cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbionts within different species of coral. Zooxanthellae within M. annularis appear to be more susceptible to heat-induced damage at or near the reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non-photochemical pathways, thereby protecting the photosystem from damage during heat exposure.
We present a methodology, called fast repetition rate (FRR) fluorescence, that measures the functional absorption cross-section (σPS II) of Photosystem II (PS II), energy transfer between PS II units (p), photochemical and nonphotochemical quenching of chlorophyll fluorescence, and the kinetics of electron transfer on the acceptor side of PS II. The FRR fluorescence technique applies a sequence of subsaturating excitation pulses (‘flashlets’) at microsecond intervals to induce fluorescence transients. This approach is extremely flexible and allows the generation of both single-turnover (ST) and multiple-turnover (MT) flashes. Using a combination of ST and MT flashes, we investigated the effect of excitation protocols on the measured fluorescence parameters. The maximum fluorescence yield induced by an ST flash applied shortly (10 μs to 5 ms) following an MT flash increased to a level comparable to that of an MT flash, while the functional absorption cross-section decreased by about 40%. We interpret this phenomenon as evidence that an MT flash induces an increase in the fluorescence-rate constant, concomitant with a decrease in the photosynthetic-rate constant in PS II reaction centers. The simultaneous measurements of σPS II, p, and the kinetics of Q−A reoxidation, which can be derived only from a combination of ST and MT flash fluorescence transients, permits robust characterization of the processes of photosynthetic energy-conversion.
Coral bleaching has been defined as a general phenomenon, whereby reef corals turn visibly pale because of the loss of their symbiotic dinoflagellates and/or algal pigments during periods of exposure to elevated seawater temperatures. During the summer of 1997, seawater temperatures in the Florida Keys remained at or above 30 degrees C for more than 6 weeks, and extensive coral bleaching was observed. Bleached colonies of the dominant Caribbean reef-building species, Montastrea faveolata and Montastrea franksi, were sampled over a depth gradient from 1 to 17 m during this period of elevated temperature and contained lower densities of symbiotic dinoflagellates in deeper corals than seen in previous "nonbleaching" years. Fluorescence analysis by pulse-amplitude modulation fluorometry revealed severe damage to photosystem II (PSII) in remaining symbionts within the corals, with greater damage indicated at deeper depths. Dinoflagellates with the greatest loss in PSII activity also showed a significant decline in the D1 reaction center protein of PSII, as measured by immunoblot analysis. Laboratory experiments on the temperature-sensitive species Montastrea annularis, as well as temperature-sensitive and temperature-tolerant cultured symbiotic dinoflagellates, confirmed the temperature-dependent loss of PSII activity and concomitant decrease in D1 reaction center protein seen in symbionts collected from corals naturally bleached on the reef. In addition, variation in PSII repair was detected, indicating that perturbation of PSII protein turnover rates during photoinhibition at elevated temperatures underlies the physiological collapse of symbionts in corals susceptible to heat-induced bleaching.
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