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Cyanobacteria in the genus Acaryochloris are the only known oxyphototrophs that have exchanged chlorophyll a (Chl a) with Chl d as their primary photopigment, facilitating oxygenic photosynthesis with near infrared (NIR) light. Yet their ecology and natural habitats are largely unknown. We used hyperspectral and variable chlorophyll fluorescence imaging, scanning electron microscopy, photopigment analysis and DNA sequencing to show that Acaryochloris-like cyanobacteria thrive underneath crustose coralline algae in a widespread endolithic habitat on coral reefs. This finding suggests an important role of Chl d-containing cyanobacteria in a range of hitherto unexplored endolithic habitats, where NIR light-driven oxygenic photosynthesis may be significant. © 2011 International Society for Microbial Ecology. All rights reserved.

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0. 95 mmol O2 m-2 h-1 (~11. 7 mg C m-2 h-1) while from the sediment it was 6. 08 mmol O2 m-2 h-1 (~70. 8 mg C m-2 h-1). When the ice was present O2 export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3. 77 mg C (mg Chl-a)-1 h-1 while those from the benthos were up to 1. 53 mg C (mg Chl-a)-1 h-1. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55-65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production. © 2010 Springer-Verlag.

The persistence of tropical coral reefs is threatened by rapidly increasing climate warming, causing a functional breakdown of the obligate symbiosis between corals and their algal photosymbionts (Symbiodinium) through a process known as coral bleaching. Yet the potential of the coral-algal symbiosis to genetically adapt in an evolutionary sense to warming oceans is unknown. Using a quantitative genetics approach, we estimated the proportion of the variance in thermal tolerance traits that has a genetic basis (i.e. heritability) as a proxy for their adaptive potential in the widespread Indo-Pacific reef-building coral Acropora millepora. We chose two physiologically different populations that associate respectively with one thermotolerant (Symbiodinium clade D) and one less tolerant symbiont type (Symbiodinium C2). In both symbiont types, pulse amplitude modulated (PAM) fluorometry and high performance liquid chromatography (HPLC) analysis revealed significant heritabilities for traits related to both photosynthesis and photoprotective pigment profile. However, quantitative real-time polymerase chain reaction (qRT-PCR) assays showed a lack of heritability in both coral host populations for their own expression of fundamental stress genes. Coral colony growth, contributed to by both symbiotic partners, displayed heritability. High heritabilities for functional key traits of algal symbionts, along with their short clonal generation time and high population sizes allow for their rapid thermal adaptation. However, the low overall heritability of coral host traits, along with the corals' long generation time, raise concern about the timely adaptation of the coral-algal symbiosis in the face of continued rapid climate warming. © 2010 Császár et al.

The ecological success of reef-building corals throughout the tropics is due in large part to the endosymbiotic dinoflagellates that reside within the gastrodermal cells of these cnidarian hosts. These algae, belonging to the genus Symbiodinium, are often referred to by the common term of “zooxanthellae.” This mutualism between Symbiodinium spp. and tropical and sub-tropical coral species has been a key component to the evolutionary persistence of reef-building corals since the Triassic (Stanely 2003). The importance of these algae in the long-term success of reef-building corals cannot be over emphasized, as they can contribute a significant portion of photosynthetically derived carbon to the host via translocation. The coral metabolizes this carbon, thereby meeting up to 90 percent or more of the animal’s daily metabolic demand from the byproducts of photosynthesis by the symbionts (Muscatine 1990). The large proportion of respiratory carbon provided by these endosymbionts contributes directly to the energetic demands of coral, with calcification rates that are typically elevated by three times as much when compared to corals held in the dark or species that do not harbor endosymbionts (i.e. aposymbiotic) (Gattuso 1999). Corals also feed heterotrophically; however this energy source cannot be directly monitored using the techniques described in this chapter and consequently will not be discussed.

International audience; The physiological state of a chloroplast is stronglyinfluenced by both biotic and abiotic conditions.Unfavourable growth conditions lead to photosyntheticstress. Chlorophyll a fluorescence is a widelyused probe of photosynthetic activity (specificallyPSII), and therefore stress which specifically targetsthe electron transport pathway and associated alternativeelectron cycling pathways. By manipulating theprocesses that control photosynthesis, affecting thechlorophyll a fluorescence, yields detailed insight intothe biochemicalpathways. Light that is captured by achlorophyll molecule can be utilised in three competingprocesses; electron transport, energy dissipation(via heat) and chlorophyll a fluorescence emission.Electrons produced by water-splitting are not alwaysused in carbon fixation; if the incident irradiancegeneratesmore electrons than the dark reactionscan use in carbon fixation, damage will occur to the photosynthetic apparatus. If carbon fixation is inhibitedby temperature or reduced inorganic carbon (Ci), ATPor NADPH availability, then the photosystem dynamicallyadjusts and uses alternate sinks for electrons, suchas molecular oxygen (water-water cycle or Mehler ascorbateperoxidase reaction). The process of stress acclimationleads to a number of photoprotective pathwaysand we describe how inhibitors can be used to identifythese particular processes. In this chapter, we describethe processes controlling electron transport as influencedby light-induced stress.

Rhizomes of Posidonia australis Hook. f., collected from Botany Bay on the eastern coast of Australia, were analyzed for extractable carbohydrates. The concentration of extractable carbohydrate in the stelar tissue of the rhizome was significantly higher than that in the surrounding cortex. Reduced concentrations of extractable carbohydrate reserves were found in juvenile tissue and tissue adjacent to the apical meristem. Unexpanded internodes contained higher concentrations of extractable carbohydrate than expanded internodes. Tissue from equivalent positions along both the lateral and parental axis of a rhizome branch showed similar extractable carbohydrate levels and had similar patterns of internodal length. The pattern of carbohydrate storage within the rhizomatous tissue of P. australis is closely related to the age and health of the plant.

Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. The expulsion of the symbiotic dinoflagellate algae is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. Here, the sensitivity of the oxygen evolving complex (OEC) to bleaching stress was studied as well as its natural variation between seasons. The artificial electron donor, diphenyl carbazide (DPC), was added to cultured, freshly isolated and expelled (bleaching treatments only) zooxanthellae suspensions. Chl a fluorescence and oxygen production measurements showed that upon addition of DPC, no restoration of diminished photochemical efficiency occurred under control or bleaching conditions. This result was consistent between 12 h and 5 d bleaching treatments on Pocilloporadamicornis, indicating that the OEC is not the primary site of damage, and that zooxanthellae expulsion from the host is a nonselective process with respect to the functioning of the OEC. Further experiments measuring fast induction curves (FICs) revealed that in both summer and winter, the temperature when OEC function was lost occurred between 7°C and 14°C above the sea surface temperature. FIC and oxygen production measurements of P. damicornis during exposure to bleaching stress demonstrated that the thermotolerance of the OEC increased above the temperature of the bleaching treatment over a 4 h period. This finding indicates that the OEC has the capacity to acclimate between seasons and remains functional at temperatures well above bleaching thresholds. © 2008 Phycological Society of America.

Physiological plasticity has the capacity to prolong seagrass survival under reduced light conditions. However, when light is attenuated across a depth gradient, the relative importance of this over other mechanisms for tolerating long-term light reduction (such as morphological adjustments and shoot loss) has been guestioned. This study aimed to describe a number of the physiological characteristics of Posidonia sinuosa Cambridge et Kuo along a depth-related gradient of light availability (1.6 to 9.0 m depth) and infer how these characteristics are important for the long-term maintenance of the meadow. Rapid light curve-derived parameters, light harvesting pigments, photoprotective pigments and nutrient and carbohydrate concentrations exhibited few differences among depth strata, but showed some (albeit limited) adjustment between the seasons. It was inferred that some physiological plasticity is possible in P. sinuosa but that differences in the depth-related gradient of long-term light availability were not sufficient to induce physiological differences, even at the depth limit. Shoot density reductions, which reduce the effects of self-shading, possibly offset depth-related light reductions. Because the physiological characteristics we examined did not explain the adaptations by P. sinuosa to the long-term gradient of light availability, they may not be useful indicators of long-term light reduction. © Inter-Research 2008.

Coral bleaching events have been linked to elevated seawater temperatures in combination with intense light and can be characterised by the loss of symbionts (zooxanthellae, genus Symbiodinium) from the host tissue, as well as a reduction in photosynthetic pigments in these zooxanthellae. The long-term (days) viability of expelled zooxanthellae in the water column from the scleractinian coral Pocillopora damicornis was explored in this study through measurements of photosynthetic health and morphological condition. After initial expulsion, zooxanthellae were found to be photosynthetically competent and structurally intact. However, within 6 to 12 h following this time, photosystem II photochemical efficiency dramatically declined in these cells and photosynthetic damage was gradually manifested in the loss of structural integrity of the cell. The time of expulsion during bleaching exposure, as well as ambient water temperature, greatly influenced survivorship. Expelled zooxanthellae were collected at 4 different time intervals (0-6, 6-12, 12-24 and 24-36 h) following the onset of exposure to bleaching conditions (32°C and 400 μmol photons m-2 s-1) and then maintained at 28, 30 or 32°C and 100 μmol photons m-2 s-1 for up to 96 h. Those cells expelled within the first 6 h of bleaching and held at 28°C (lagoon temperature) had the greatest longevity, although even in this treatment, long-term photosynthetic viability was restricted to 5 d in the water column. This suggests that unless expelled zooxanthellae inhabit other environments of coral reefs (such as sediments) which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. © Inter-Research 2007.

Growth inhibition bioassays with the microalga Nitzschia closterium have recently been applied in marine Toxicity Identification Evaluation (TIE) testing. However, the 48-h test duration can result in substantial loss of toxicants over time, which might lead to an underestimation of the sample toxicity. Although shorter-term microalgal bioassays can minimize such losses, there are few bioassays available and none are adapted for marine TIE testing. The acute (5-min) chlorophyll-a fluorescence bioassay is one alternative; however, this bioassay was developed for detecting herbicides in freshwater aquatic systems and its suitability for marine TIE testing was not known. In this study, a chlorophyll-a fluorescence bioassay using the marine microalga Isochrysis galbana was able to detect contaminants other than herbicides at environmentally relevant concentrations and tolerated the physical and chemical manipulations needed for a Phase I TIE. Phase I TIE procedures were successfully developed using this chlorophyll-a fluorescence bioassay and used to identify all classes of contaminants present in a synthetic mixture of known chemical composition. In addition, TIEs with both the acute fluorescence bioassay and the standard growth inhibition bioassay identified the same classes of toxicants in a sample of an unknown complex effluent. Even though the acute chlorophyll-a fluorescence end point was less sensitive than the chronic cell division end point, TIEs with the chlorophyll-a fluorescence bioassay provided a rapid and attractive alternative to longer-duration bioassays.

Coral bleaching caused by global warming is one of the major threats to coral reefs. Very recently, research has focused on the possibility of corals switching symbionts as a means of adjusting to accelerating increases in sea surface temperature. Although symbionts are clearly of fundamental importance, many aspects of coral bleaching cannot be readily explained by differences in symbionts among coral species. Here we outline several potential mechanisms by which the host might influence the bleaching response, and conclude that predicting the fate of corals in response to climate change requires both members of the symbiosis to be considered equally. © 2008 Elsevier Ltd. All rights reserved.

We used microscopy, reflectance spectroscopy, pigment analysis, and photosynthesis-irradiance curves measured with variable fluorescence techniques to characterise the endolithic communities of phototrophic microorganisms in the skeleton of three massive corals from a shallow reef flat. Microscopic observations and reflectance spectra showed the presence of up to four distinct bands of photosynthetic microorganisms at different depths within the coral skeleton. Endolithic communities closer to the coral surface exhibited higher photosynthetic electron transport rates and a green zone dominated by Ostreobium quekettii nearest the surface had the greatest chlorophyll pigment concentration. However, Ostreobium was also present and photosynthetically active in the colourless band between the coral tissue and the green band. The spectral properties and pigment density of the endolithic bands were also found to closely correlate to photosynthetic rates as assessed by fluorometry. All endolithic communities were extremely shade-adapted, and photosynthesis was saturated at irradiances

Growth of human populations along coastal environments, as well as poor water management practices have resulted in the complete loss of seagrass meadows (Kemp et al., 1983; Larkum and West, 1990; Short and Wyllie-Echeverria, 1996; Peters et al., 1997). For example, the catastrophic loss of seagrasses clearly illustrated in Fig. 1 is linked to coastal development and associated reduction in water quality. © 2006/2007 Springer. All Rights Reserved.

Chlorophyll a fluorescence has the potential to become a valuable ecotoxicological endpoint, which could be used with a range of aquatic phototrophs. Chlorophyll a fluorescence bioassays have been applied in the assessment of heavy metals, herbicides, petrochemicals and nutrients. The strengths of this endpoint are that it is rapid, non-invasive and non-destructive, while the major weakness is the lack of clear ecological relevance. We provide an overview of chlorophyll a fluorescence applications in ecotoxicology. We reviewed test conditions, parameters and protocols used to date and found standardised protocols to be lacking. The most favoured fluorescence parameters were maximum quantum yield (Fv/Fm) and effective quantum yield (ΦPSII); microalgae were the most widely used tested organism, herbicides the most commonly tested toxicant, while most studies lacked a summary statistic (such as EC50). We recommend that future research in aquatic chlorophyll a fluorescence ecotoxicology focus on standardisation of test protocols and statistical techniques. © 2007 Taylor & Francis.

Seagrasses are marine angiosperms from the Families Potamagetonaceae and Hydrocharitaceae (Chapter 1). These are by origin land plants that developed both aerial photosynthesis and aerial flowering and then returned to a successful fully submerged marine habitat, from where their algal forbears derived. Following the evolution of land plants there have been few developments in terms of photosynthesis: the only outstanding developments being adaptations to arid conditions, such as the development of C4 photosynthesis in semi-arid plants and Crassulacean Acid Metabolism (CAM) in plants from desert regions (Bowes et al. 2002). © 2006/2007 Springer. All Rights Reserved.

The effect of diel oscillations in light on the photosynthetic response of three coral species during summer and winter was studied. Fast induction curves revealed detailed information on primary photochemistry as well as redox states of electron acceptors in photosystem II (PSII). The comparison between seasons revealed that similar physiological mechanisms were operating in response to high-light conditions throughout the year and that environmental variables, such as temperature, had no measurable effect between seasons. A diurnal hysteresis was seen in both seasons in Fv / Fm as well as in the fast induction curves, where photosynthetic capacity was lower in the afternoon than in the morning when light intensities were the same. This suggests the operation of dynamic down regulation, following exposure to midday high light. Fast induction curve analysis revealed a decline in the O, J, I and P steps towards midday and a rapid recovery by the late afternoon. The decrease in J and its rapid recovery indicated a drop in the rate of QA reduction as a result of an increase in non-photochemical quenching (NPQ). The P step increased in amplitude in the first hours of sunlight, which suggests an increased oxidation of the plastoquinone (PQ) pool and a greater capacity for electron transport. Similarly, a rise in Fv / Fm was observed within the first hour of sunlight. This response was attributed to the dark reduction of the PQ pool, induced by night time anaerobic conditions and possibly oxygen-dependent chlororespiration, which would lead to a state 2 transition. The early morning removal of chlororespiration and hypoxic conditions would have returned the photosystems to state 1, resulting in the increased photochemical efficiency of the zooxanthellae.

Rapid light curves provide detailed information on the saturation characteristics of electron transport, as well as the overall photosynthetic performance of a plant. Rapid light curves were collected from samples of Zostera marina grown under low and high-light conditions (50 and 300 μmol photons m-2 s-1) and the distinctive patterns of RLC parameters are discussed, in terms of differential sink capacity and PSII reaction centre closure. Derived cardinal points of a rapid light curve (α, Ek and rETRmax) describe the photosynthetic capacity of a seagrass leaf, its light adaptation state and its capacity to tolerate short-term changes in light. The shapes of the corresponding F and F′m curves also provide information on the development of the trans-thylakoid proton gradient and thermal energy dissipation. Low-light leaves showed limited photosynthetic capacity and reduced activity of non-photochemical quenching pathways, whereas photosynthesis of high light leaves were not limited and showed an elevated level of non-photochemical quenching, possibly associated with xanthophyll cycle activity. Light-dark kinetics are also discussed in relation to relaxation of non-photochemical quenching and its various components. A curve fitting model is recommended based on the double exponential decay function. In this paper, we explain the fundamental aspects of a RLC, describe how it reflects the response to light exposure of a leaf, how to interpret these curves, and how to quantitatively describe and compare RLCs. © 2005 Elsevier B.V. All rights reserved.

Hormosira banksii is a morphologically variable macroalgal species from southeastern and southern Australia, which has been previously categorised into ecoforms according to habitat. This study is by far the largest quantitative evaluation of morphological variation in H. banksii, covering 74 sites from South Australia, Victoria, New South Wales and Tasmania. Morphological features from 505 samples were analysed using principal components analysis, with the patterns identified being statistically assessed with a Monte Carlo permutation test. There was considerable morphological variation between samples taken at several marine (but not estuarine) sites in both 1994 and 1999. However, this variation was not consistent across either morphological features or populations, and presumably represents random fluctuations. Analysis of the entire dataset demonstrated a significant difference between samples growing in marine and estuarine habitats. Further assessment of variation within these two groups revealed some significantly different populations based on geographical locations but not habitat variation. While this study presents strong evidence for two distinct taxa within H. banksii (marine versus estuarine populations), the taxonomic status of this species should not be altered until genetic studies have been conducted. © 2005 by Walter de Gruyter.

Bleaching is a worldwide phenomenon affecting coral reefs. During elevated temperature and light conditions (bleaching), expelled zooxanthellae show distinct patterns in photosynthetic health. An innovative new device was used to collect individual expelled zooxanthellae, when a coral was exposed to bleaching conditions. This has provided new insight into the photosynthetic condition and abundance of expelled zooxanthellae. It has been assumed that expelled zooxanthellae were dead or moribund; however, we have found individual cells can have healthy effective quantum yields (φPSII) >0.65 after 8 h of bleaching conditions (500 μmol photons m-2 s -1, 33°C). The population of expelled zooxanthellae from Cyphastrea serailia and Pocillopora damicornis showed distinct patterns in the frequency distribution of φPSII over time and between locations (sun versus shade) within a colony. During the first 4 h of exposure to bleaching conditions, only 5% of expelled individual cells from P. damicornis were photosynthetically inactive (φPSII

The cyanobacterium known as Acaryochloris marina is a unique phototroph that uses chlorophyll d as its principal light-harvesting pigment instead of chlorophyll a, the form commonly found in plants, algae and other cyanobacteria; this means that it depends on far-red light for photosynthesis. Here we demonstrate photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates (didemnid ascidians) in a shaded niche enriched in near-infrared light. This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat.

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27°C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16 ± 1.0 μg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 μg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758 ± 35 μg l-1 with a MDEC of 112 μg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P ≤ 0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines. © 2005 Elsevier Ltd. All rights reserved.

Sea-ice brine algal communities were exposed to salinities between 30 and 10‰ during melting. There was a progressive decline in maximum quantum yield, relative electron transfer rate (rETRmax) and photosynthetic efficiency (α) with decreasing salinity of the final melted sample. While all species showed a drop in these parameters, Fragilariopsis curta and Entomoneis kjellmannii showed the least inhibition. There was a steady increase in rETRmax and alpha; over 5 days after melting, especially in the samples melted into the highest salinities. In addition, the samples melted from the ice without added filtered seawater showed no photosynthetic activity after 2 days. Our results suggest that for experimental work using sea-ice microalgae, the final salinity of the melted sample should be greater than 28‰ (i.e. the ratio of sea ice to filtered seawater should be at least 1:2). © Springer-Verlag 2004.

The innovative bioassay described here involves chlorophyll a fluorescence measurements of gametes from the macroalgae, Hormosira banksii, where gametes (eggs) were exposed to Diuron, Irgarol and Bromacil. Response was assessed as percent inhibition from control of effective quantum yield (ΔF/Fm′) of photosystem II, herein referred to as % PSII Inhibition. This was measured with the dual-channelled pulse amplitude modulated (PAM) fluorometer, ToxY-PAM. The fluorescence bioassay was run simultaneously with an established H. banksii germination bioassay to compare sensitivity, precision, and time-to-result. The fluorescence bioassay gave highly sensitive results evidenced by EC 50s (% PSII Inhibition) for Diuron, Irgarol and Bromacil being three, four and three orders of magnitude (respectively) lower than EC50s generated from the germination bioassays. Precision of the fluorescence bioassay was demonstrated with low coefficient of variations (

Heterogeneity in photosynthetic performance between polyp and coenosarc tissue in corals was shown using a new variable fluorescence imaging system (Imaging-PAM) with three species of coral, Acropora nobilis, Cyphastrea serailia and Pocillopora damicornis. In comparison to earlier studies with fibre-optic microprobes for fluorescence analysis, the Imaging-PAM enables greater accuracy by allowing different tissues to be better defined and by providing many more data points within a given time. Spatial variability of photosynthetic performance from the tip to the distal parts was revealed in one species of branching coral, A. nobilis. The effect of bleaching conditions (33°C vs. 27°C) was studied over a period of 8 h. Marked changes in fluorescence parameters were observed for all three species. Although a decline in ΦPSII (effective quantum yield) and Yi (the first effective quantum yield obtained from a rapid light curve) were observed, P. damicornis showed no visual signs of bleaching on the Imaging-PAM after this time. In A. nobilis and C. serailia, visual signs of bleaching over the 8 h period were accompanied by marked changes in F (light-adapted fluorescence yield), NPQ (non-photochemical quenching) and E k (minimum saturating irradiance), as well as ΦPSII and Yi. These changes were most marked over the first 5 h. The most sensitive species was A. nobilis, which after 8 h at 33°C had reached a ΦPSII value of almost zero across its whole surface. Differential bleaching responses between polyps and coenosarc tissue were found in P. damicornis, but not in A. nobilis and C. serailia. NPQ increased with exposure time to 33°C in both the latter species, accompanied by a decreasing E k, suggesting that the xanthophyll cycle is entrained as a mechanism for reducing the effects of the bleaching conditions.

We used photosynthetic activity (measured as chlorophyll a fluorescence) and photosynthetic pigment concentrations to assess the effect of pulsed exposures of aged crude oil (Champion Crude), dispersant (VDC) and an oil + dispersant mixture on the seagrass Zostera capricorni Aschers in laboratory and field experiments, using custom-made chambers. Samples were exposed for 10 h to 0.25% and 0.1% concentrations of aged crude oil and dispersant as well as mixtures of 0.25% oil + 0.05% dispersant and 0.1% oil + 0.02% dispersant. During this time and for the subsequent four day recovery period, the maximum and effective quantum yields of photosystem II (Fv/Fm and ΔF/Fm′ respectively) were measured. In the laboratory experiments, both values declined in response to oil exposure and remained low during the recovery period. Dispersant exposure caused a decline in both values during the recovery period, while the mixture of aged crude oil + dispersant had little impact on both quantum yields. In situ samples were less sensitive than laboratory samples, showing no photosynthetic impact due to dispersant and oil + dispersant mixture. Despite an initial decline in ΔF/Fm′, in situ oil-exposed samples recovered by the end of the experiment. Chlorophyll pigment analysis showed only limited ongoing impact in both laboratory and field situations. This study suggests that laboratory experiments may overestimate the ongoing impact of petrochemicals on seagrass whilst the dispersant VDC can reduce the impact of oil on seagrass photosynthesis.

Tides and freshwater inflow which influence water movement in estuarine areas govern the exposure-regime of pollutants. In this experiment, we examined the in situ impact of double pulses of copper and the herbicide Irgarol 1051 on the photosynthesis of the seagrass, Zostera capricorni . Despite a 4-day recovery period between the two 10 h pulses of toxicant, the effective quantum yield of photosystem II (Δ F /Fm′) and total chlorophyll concentrations indicated that multiple-pulses had a greater impact than a single pulse. During the first exposure period, samples exposed to Irgarol 1051 had Δ F /Fm′ values as low as zero while controls remained around 0.6 relative units. After the second exposure period, treated samples recovered to only 0.4 relative units. Samples exposed to copper had Δ F /Fm′ values around 0.3 relative units during the first exposure period and while these samples recovered before the second dose, they remained below 0.2 relative units after the second exposure period. Alternate samples were also exposed to one toxicant, allowed to recover and then exposed to the other toxicant. Δ F /Fm′ values indicated that copper exposure followed by Irgarol 1051 exposure was more toxic than Irgarol 1051 exposure followed by copper exposure.

Chlorophyll-a fluorescence was measured in six species of coral, using pulse-amplitude-modulated fluo- rometers employing fibre-optic probes with diameters of 8 mm, 1 mm and 140 lm. The 8-mm probe integrated responses over a large area, giving more weight to coe- nosarc than polyp tissue for Acropora nobilis. With 1-mm and 140-lm fibre-optic probes, the photosynthetic re- sponses of zooxanthellae in the coenosarc and the polyp tissue of Acropora nobilis were distinguished. The polyp tissue exhibited a lower maximum in relative electron transport rate than did the coenosarc tissue, and was subject to down-regulation at higher irradiances. Coe- nosarc and polyp tissue (both containing zooxanthellae) showed a wide range of responses in the other corals. Down-regulation of photosynthesis in a single polyp of Pocillopora damicornis was followed after exposure to moderate irradiance, with recovery occurring over a further 4 h of shade conditions. All the corals (Acropora millepora, A. nobilis, Cyphastrea serailia, Montipora tuberculosa, Pocillopora damicornis and Porites cylindri- ca) showed evidence of strong down-regulation of pho- tosynthesis under high irradiance, and little evidence of photoinhibitory damage to photosystem II.

A matrix of photobioreactors integrated with metabolic sensors was used to examine the combined impact of light and temperature variations on the growth and physiology of the biofuel candidate microalgal species Nannochloropsis oculata. The experiments were performed with algal cultures maintained at a constant 20u C versus a 15°C to 25°C diel temperature cycle, where light intensity also followed a diel cycle with a maximum irradiance of 1920 μmol photons m-2 s-1. No differences in algal growth (Chlorophyll a) were found between the two environmental regimes; however, the metabolic processes responded differently throughout the day to the change in environmental conditions. The variable temperature treatment resulted in greater damage to photosystem II due to the combined effect of strong light and high temperature. Cellular functions responded differently to conditions before midday as opposed to the afternoon, leading to strong hysteresis in dissolved oxygen concentration, quantum yield of photosystem II and net photosynthesis. Overnight metabolism performed differently, probably as a result of the temperature impact on respiration. Our photobioreactor matrix has produced novel insights into the physiological response of Nannochloropsis oculata to simulated environmental conditions. This information can be used to predict the effectiveness of deploying Nannochloropsis oculata in similar field conditions for commercial biofuel production. © 2014 Tamburic et al.

Increased ocean temperatures are thought to be triggering mass coral bleaching events around the world. The intracellular symbiotic zooxanthellae (genus Symbiodinium) are expelled from the coral host, which is believed to be a response to photosynthetic damage within these symbionts. Several sites of impact have been proposed, and here we probe the functional heterogeneity of Photosystem II (PSII) in three coral species exposed to bleaching conditions. As length of exposure to bleaching conditions (32°C and 350 μmol photons m-2 s-1) increased, the QA- reoxidation kinetics showed a rise in the proportion of inactive PSII centers (PSIIX), where QB was unable to accept electrons. PSIIX contributed up to 20% of the total PSII centers in Pocillopora damicornis, 35% in Acropora nobilis and 14% in Cyphastrea serailia. Changes in Fv/Fm and amplitude of the J step along fast induction curves were found to be highly dependent upon the proportion of . PSII X centers within the total pool of PSII reaction centers. Determination of PSII antenna size revealed that under control conditions in the three coral species up to 60% of PSII centers were lacking peripheral light-harvesting complexes (PSIIβ). In P. damicornis, the proportion of PSIIβ increased under bleaching conditions and this could be a photoprotective mechanism in response to excess light. The rapid increases in PSIIX and PSIIβ observed in these corals under bleaching conditions indicates these physiological processes are involved in the initial photochemical damage to zooxanthellae. © 2006 American Society for Photobiology.

The cyanobacterium known as Acaryochloris marina is a unique phototroph that uses chlorophyll d as its principal light-harvesting pigment instead of chlorophyll a, the form commonly found in plants, algae and other cyanobacteria; this means that it depends on far-red light for photosynthesis. Here we demonstrate photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates (didemnid ascidians) in a shaded niche enriched in near-infrared light. This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat.

Growth, pigment levels and various photosynthesis parameters were measured in expanding leaves of Corymbia gummifera (Solander ex Gaertner) Hochreutiner. C. gummifera trees were studied growing in sandstone plateau woodland communities in Royal National Park, New South Wales, in a recently burned open habitat. Young leaves (horizontally oriented to maximise light exposure) were found to be conspicuously red until they reached approximately 75% of their full size. As the leaves expanded, anthocyanin content declined and chlorophyll levels proportionately increased. Young red leaves showed net negative carbon assimilation rates, although CO2 assimilation rate, transpiration rate, stomatal conductance, actual quantum yield of PSII (ΦPSII) and apparent electron transport rate (ETR) all increased in a similar pattern as the leaves expanded. Measurements of maximum quantum yield of dark-adapted leaves (Fv/Fm) were also correlated with leaf area. Younger leaves had lower Fv/Fm ratios than did mature leaves, whether measured at midday or 2 h after sunset, indicating that young leaves exhibited some degree of chronic photoinhibition. It is concluded that C. gummifera exhibits a transient red pattern of anthocyanin expression and that photosynthesis is limited in young leaves because of low stomatal conductance, low chlorophyll content, immature chloroplasts and an attenuation of light caused by anthocyanins.

Changes in the photobiology and photosynthetic pigments of the seagrass Zostera marina from Chesapeake Bay (USA) were examined under a range of natural and manipulated irradiance regimes. Photosynthetic activity was assessed using chlorophyll-a fluorescence, and photosynthetic pigments were measured by HPLC. Large changes in the violaxanthin, zeaxanthin, and antheraxanthin content were concomitant with the modulation of non-photochemical quenching (NPQ). Photokinetics (Fv/Fm, rapid light curves (RLC), and non-photochemical quenching) varied as a result of oscillating irradiance and were highly correlated to xanthophyll pigment content. Zeaxanthin and antheraxanthin concentrations increased under elevated light conditions, while violaxanthin increased in darkened conditions. Unusually high concentrations of antheraxanthin were found in Z. marina under a wide range of light conditions, and this was associated with the partial conversion of violaxanthin to zeaxanthin. These results support the idea that xanthophyll intermediate pigments induce a photoprotective response during exposure to high irradiances in this seagrass.

Shallow water coral reefs may experience hypoxia under conditions of calm weather doldrums. Anaerobic responses of endosymbionts (i.e. zooxanthellae) within Pocillopora damicornis coral colonies were tested using both slow and fast chlorophyll a fluorescence induction kinetics. Zooxanthellae were examined in hospite when exposed to control conditions (26°C, 200 μmol photons m-2 s-1, 100% air-saturation, 4 cm s-1 flow) and to 2 treatments of reduced air content (40 and 0%), achieved by controlling the N2:O2 ratio in water circulating at 2 cm s -1. Furthermore, the impact of water flow on photosynthesis was examined at 0% air saturation by turning off the flow entirely (0 cm s -1), thereby mimicking the environmental conditions of calm weather doldrums. Corals exposed to depleted air content (0 % with and without flow) showed a significant decrease (p < 0.001) in effective quantum yield (φPSII) in comparison with controls. Maximum quantum yield was significantly reduced when gas exchange was inhibited (0% without flow), whereas non-photochemical quenching (NPQ) was not affected. Fast polyphasic fluorescence transients of chlorophyll a fluorescence showed a significant increase in minimum dark-adapted fluorescence, F0, when corals were exposed to anaerobic conditions. Furthermore, an increase in the J peak (2 ms) corresponding to the reduction of the primary electron acceptor, QA, was observed in 0% air-saturation with flow. We found that the most sensitive parameters for detecting physiological change associated with hypoxia were φPSII using slow (pulse-amplitude modulation) fluorescence kinetics, as well as an increase in the O peak, φPo(electron transport efficiency before QA), and an elevation of the J peak on a double-normalised transient using fast (Plant Efficiency Analyser) induction kinetics. © Inter-Research 2005.

© 2016 Chartrand, Bryant, Carter, Ralph and Rasheed. Coastal seagrass habitats are at risk from a range of anthropogenic activities that modify the natural light environment, including dredging activities associated with coastal and port developments. On Australia's east coast, the tropical seagrass Zostera muelleri ssp. capricorni dominates intertidal mudbanks in sheltered embayments which are also preferred locations for harbors and port facilities. Dredging to establish and maintain shipping channels in these areas can degrade water quality and diminish light conditions that are required for seagrass growth. Based on this potential conflict, we simulated in-situ light attenuation events to measure effects on Z. muelleri ssp. capricorni condition. Semi-annual in situ shading studies conducted over 3 years were used to quantify the impact of prolonged light reduction on seagrass morphometrics (biomass, percent cover, and shoot density). Experimental manipulations were complimented with an assessment of 46 months of light history and concurrent natural seagrass change at the study site in Gladstone Harbour. There was a clear light-dependent effect on seagrass morphometrics during seagrass growing seasons, but no effect during senescent periods. Significant seagrass declines occurred between 4 and 8 weeks after shading during the growing seasons with light maintained in the range of 4-5 mol photons m-2 d-1. Sensitivity to shading declined when applied in 2-week intervals (fortnightly) rather than continuous over the same period. Field observations were correlated to manipulative experiments to derive an applied threshold of 6 mol photons m-2 d-1 which formed the basis of a reactive light-based management strategy which has been successfully implemented to ensure positive ecological outcomes for seagrass during a large-scale dredging program.

Coral surface temperature was investigated with multiple temperature sensors mounted on hemispherical and branching corals under (a) artificial lighting and controlled flow; (b) natural sunlight and controlled flow; and (c) in situ conditions in a shallow lagoon, under naturally fluctuating irradiance, water flow, and temperature. Under high irradiance and low flow conditions, hemispherical corals were 0.6°C warmer than the surrounding water. Hemispherical corals reached higher temperatures than branching corals, by a measure of 0.2°C to 0.4°C. Microsensor temperature measurements showed the presence of a thermal boundary layer (TBL). The TBL thickness was flow dependent, and under low flow conditions, a TBL up to 3 mm thick limited heat transfer to the ambient water. Combined microsensor measurements of temperature and oxygen showed that the TBL was approximately four times thicker than the diffusive boundary layer, as predicted from heat and mass transfer theory. A simple conceptual model describes coral surface temperature as a function of heat fluxes between coral tissue, skeleton, and surroundings. The slope of the predicted linear relationship between coral temperature and solar irradiance is fixed by the efficiencies of light absorption and the heat losses to the skeleton and the water. Although spectral absorptivity may play a significant role in coral warming, shape-related differences in thermal properties can cause hemispherical corals to reach higher temperatures than branching corals. Shape-related differences in thermal histories may thus help explain differences in susceptibility to coral bleaching between branching and hemispherical coral species. © 2008, by the American Society of Limnology and Oceanography, Inc.

Hormosira banksii shows a considerable degree of morphological variability throughout its range in south-eastern Australia, apparently in relation to the local habitat, and there have been several previous qualitative attempts to categorize this variation by recognizing ecoforms. From our quantitative morphometric analyses of plants from 21 sites covering 300 km of coastline in south-eastern Australia, using multiple discriminant function analysis based on seven vesicle characteristics (measuring size and shape), there is very little evidence of intergrading forms. The morphological variation is not multivariately continuous, as has been previously suggested, although each individual attribute does show more-or-less continuous variation, and the morphological variation is not a simple reflection of habitat but reflects more complex microhabitat relationships. The morphological forms that we recognize are multivariate, and thus all of the attributes need to be considered. In particular, volume (or surface area:volume ratio) is usually a very good discriminator between groups, indicating that both size and shape are important for defining the groups. We recognize two main phenotypically distinct groups, comprising plants from sheltered estuarine situations and those from exposed marine rock platforms. The vesicles of plants from the estuarine habitats are more-or-less spherical (length≈diameter), with a volume approximately 3–10 times that of vesicles from the marine plants; it is thus probable that the variation in the vesicle dimensions of these morphs can be linked to desiccation resistance. The estuarine and marine habitats are likely to be ecologically isolated from each other, and there is therefore unlikely to be a great deal of gene flow between these plants; if they are treated as separate species, then they would be H. banksii (Turner) Decaisne and H. sieberi (Bory) Decaisne, respectively. Three relatively distinct morphometric forms were also recognizable within the marine group, including plants from the bottom of rock pools; from rock pool edges and sublittoral regions; and from the surface of rock pools and exposed parts of the platforms. Two less distinctive morphometric forms were recognizable within the estuarine group, including plants from tidal flats and those from mangrove forests. The taxonomic status of these microhabitat forms remains uncertain.