John W. Runcie

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m−2 s−1. O2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm′−Ft)/Fm′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m−2 s−1), there was a significant correlation between O2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O2 evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m−2 s−1) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3−], [NH4+] and [HPO42-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.

Establishing research strategies, methodologies and technologies to link genomics and proteomics to seagrass productivity, community metabolism, and ecosystem carbon fluxes

A complete understanding of the mechanistic basis of marine ecosystem functioning is only possible through integrative and interdisciplinary research. This enables the prediction of change and possibly the mitigation of the consequences of anthropogenic impacts. One major aim of the European Cooperation in Science and Technology (COST) Action ES0609 “Seagrasses productivity. From genes to ecosystem management,” is the calibration and synthesis of various methods and the development of innovative techniques and protocols for studying seagrass ecosystems. During 10 days, 20 researchers representing a range of disciplines (molecular biology, physiology, botany, ecology, oceanography, and underwater acoustics) gathered at The Station de Recherches Sous-marines et Océanographiques (STARESO, Corsica) to study together the nearby Posidonia oceanica meadow. STARESO is located in an oligotrophic area classified as “pristine site” where environmental disturbances caused by anthropogenic pressure are exceptionally low. The healthy P. oceanica meadow, which grows in front of the research station, colonizes the sea bottom from the surface to 37 m depth. During the study, genomic and proteomic approaches were integrated with ecophysiological and physical approaches with the aim of understanding changes in seagrass productivity and metabolism at different depths and along daily cycles. In this paper we report details on the approaches utilized and we forecast the potential of the data that will come from this synergistic approach not only for P. oceanica but for seagrasses in general.

Effect of seasonal sea ice breakout on the photosynthesis of benthic diatom mats at Casey, Antarctica

Photosynthesis of marine benthic diatom mats was examined before and after sea ice breakout at a coastal site in eastern Antarctica (Casey). Before ice breakout the maximum under‐ice irradiance was between 2.5 and 8.2 μmol photons·m−2·s−1 and the benthic microalgal community was characterized by low Ek (12.1–32.3 μmol photons·m−2·s−1), low relETRmax (9.2–32.9), and high alpha (0.69–1.1). After breakout, 20 days later, the maximum irradiance had increased to between 293 and 840 μmol photons·m−2·s−1, Ek had increased by more than an order of magnitude (to 301–395 μmol photons·m−2·s−1), relETRmax had increased by more than five times (to 104–251), and alpha decreased by approximately 50% (to 0.42–0.68). During the same time interval the species composition of the mats changed, with a decline in the abundance of Trachyneis aspera (Karsten) Hustedt, Gyrosigma subsalsum Van Heurck, and Thalassiosira gracilis (Karsten) Hustedt and an increase in the abundance of Navicula glaciei Van Heurck. The benthic microalgal mats at Casey showed that species composition and photophysiology changed in response to the sudden natural increase in irradiance. This occurred through both succession shifts in the species composition of the mats and also an ability of individual cells to photoacclimate to the higher irradiances.

Levels of selected chlorinated hydrocarbons in edible fish tissues from polluted areas in the Georges/Cooks Rivers and Sydney Harbour, New South Wales, Australia

Abstract During the period from February to March 1995 edible fish were sampled from various locations known to be polluted with chlorinated hydrocarbons. Samples were collected from five locations in the Georges/Cooks Rivers and four locations in Sydney Harbour. The muscle tissue of a range of fish species from each location was analysed for selected chlorinated hydrocarbons (i.e. polychlorinated biphenyls (PCBs) and organochlorine pesticides). The Georges/Cooks Rivers locations were in Prospect Creek. Chipping Norton, Saltpan Creek, Cooks River and Alexandra Canal. The Sydney Harbour locations were in Duck River, Parramatta River, Homebush Bay, Iron Cove and Long Bay. Chlorinated hydrocarbons were found in the tissues of fish sampled from every location. The major contaminants were PCBs and the Group A organochlorine pesticides, which include chlordane, dieldrin and heptachlor epoxide. At some locations, the mean concentration of one or more of these contaminants was significantly greater than the National Food Authority Maximum Residue Limit (MRL) in certain fish species. DDT and/or its metabolites were not found above their MRL at any location, but were detected at all locations. The highest mean concentrations of PCBs were detected in fish from Prospect Creek, Chipping Norton, Duck River, Alexandra Canal and Homebush Bay. The highest mean concentrations of Group A pesticides, particularly chlordane and dieldrin, were detected in fish from Alexandra Canal, Cooks River and Duck River. The highest mean concentrations of DDT were found in the tissues of fish from Prospect Creek. The fish species which accumulated contaminants to concentrations exceeding the relevant MRLs were yellow-fin bream (Alexandra Canal, Cooks River, Saltpan Creek, Duck River, Homebush Bay and Parramatta River), sea mullet (Prospect Creek, Chipping Norton, Cooks River, Alexandra Canal, Saltpan Creek, Duck River, Homebush Bay and Iron Cove), pink-eye mullet (Prospect Creek) and silver biddy (Prospect Creek, Chipping Norton, Alexandra Canal and Iron Cove), whereas the luderick, fan-tail mullet and sand whiting had mean concentrations of contaminants below the relevant MRLs.

Identifying knowledge gaps in seagrass research and management: an Australian perspective

Seagrass species form important marine and estuarine habitats providing valuable ecosystem services and functions. Coastal zones that are increasingly impacted by anthropogenic development have experienced substantial declines in seagrass abundance around the world. Australia, which has some of the worlds largest seagrass meadows and is home to over half of the known species, is not immune to these losses. In 1999 a review of seagrass ecosystems knowledge was conducted in Australia and strategic research priorities were developed to provide research direction for future studies and management. Subsequent rapid evolution of seagrass research and scientific methods has led to more than 70% of peer reviewed seagrass literature being produced since that time. A workshop was held as part of the Australian Marine Sciences Association conference in July 2015 in Geelong, Victoria, to update and redefine strategic priorities in seagrass research. Participants identified 40 research questions from 10 research fields (taxonomy and systematics, physiology, population biology, sediment biogeochemistry and microbiology, ecosystem function, faunal habitats, threats, rehabilitation and restoration, mapping and monitoring, management tools) as priorities for future research on Australian seagrasses. Progress in research will rely on advances in areas such as remote sensing, genomic tools, microsensors, computer modeling, and statistical analyses. A more interdisciplinary approach will be needed to facilitate greater understanding of the complex interactions among seagrasses and their environment.

In situ photosynthetic rates of tropical marine macroalgae at their lower depth limit

Most photophysiological studies of marine macroalgae have focussed on algae in waters shallower than 30 m. However some species are abundant at depths in excess of 100 m with irradiances less than 1 µmol photons m−2 s−1. We examined, for the first time, the in situ efficiency of photochemical energy conversion of a variety of epilithic macroalgal species at depths from 86 to 201 m using a piloted submersible and multiple-turnover modulated chlorophyll fluorescence measurements based on the PAM technique. The irradiance at which electron transport rate reached a maximum (Ek) for green algae declined from 50 µmol photons m−2 s−1 (at ∼90 m) to less than 10 µmol photons m−2 s−1 at their lower depth limit of 140 m; photochemical quenching in response to light exposure declined markedly at depths below 100 m, while non-photochemical quenching remained low at all depths, indicating minimal photoprotective capacity in these algae. Values of Ek for encrusting Corallinales at 201 m were ∼4 µmol photons m−2 s−1, which exceeded by 400 times the maximum ambient irradiance at that depth. In the short term, the deep-water red algae examined (in particular the encrusting species) were able to tolerate and take advantage of irradiances orders of magnitude greater than the estimated noonday surface irradiance. Non-photochemical quenching of the red algae also increased with depth, indicating these algae retain their capacity for coping with high light even when in very deep waters. Carbon stable isotope data of deep algae confirmed the diffusion of inorganic carbon with its minimal energy requirement is probably the primary means of inorganic carbon uptake. The observed lower depth limits of selected macroalgae at Penguin Bank are shallower than depth limits for comparable species reported in the literature. Occasional smothering of algae by sediment, observed at Penguin Bank, would reduce the annual photon dose, thereby reducing the depth limit.

Uptake kinetics and assimilation of phosphorus by Catenella nipae and Ulva lactuca can be used to indicate ambient phosphate availability

Uptake, assimilation and compartmentation of phosphate were studied in the opportunist green macroalgaUlva lactucaand the estuarine red algal epiphyteCatenella nipae. The Michaelis–Menten model was used to describe uptake rates of inorganic phosphate (Pi) at different concentrations. Maximum uptake rates (Vmax) of P-starved material exceededVmaxof P-enriched material; this difference was greater forC. nipae. Uptake and allocation of phosphorus (P) to internal pools was measured using trichloroacetic acid (TCA) extracts and32P. Both species demonstrated similar assimilation paths: when P-enriched, most32P accumulated as free phosphate. When unenriched,32P was rapidly assimilated into the TCA-insoluble pool.C. nipaeconsistently assimilated more32P into this pool thanU. lactuca, indicatingC. nipaehas a greater P-storage capacity. In both species,32P release data showed two internal compartments with very different biological half-lives. The rapidly exchanging compartment had a short half-life of ≈2 to 12 min, while the slowly exchanging compartment had a much longer half-life of 12 days in P-starvedC. nipaeor 4 days in P-starvedU. lactuca. In both species, the slowly exchanging compartment accounted for more than 90% of total tissue.U. lactucaandC. nipaeresponded differently to high external Pi.U. lactucarapidly took up Pi, transferring this Piinto tissue phosphate and TCA-soluble P in a few hours (≈90% of total P).C. nipaetook up Piat lower rates and stored much of this P in less mobile TCA-insoluble forms. Long-term storage of refractory forms of P makesC. nipaea useful bioindicator of the prevailing conditions of Piavailability over at least the previous 7 days, whereas the P-status ofU.lactucamay reflect conditions over no more than the previous few hours or days.C. nipaeis a more useful bioindicator for P status of estuarine and marine waters thanU. lactuca.

Photosynthesis of marine macroalgae in ice-covered and ice-free environments in East Antarctica

Antarctic macroalgae survive extended periods of darkness followed by rapid and extreme increases in irradiance when sea-ice breaks out in summer. Algae from dark, ice-covered locations had low values of saturating irradiance (Ek: 4–19 µmol photons m−2 s−1), low relative rates of electron transport (rETRmax: 2.0–3.6 µmol electrons m−2 s−1) and high values of effective quantum yield (ΔF/ : 0.52–0.70). Algae from brighter open-water locations had high Ek (13–67), high rETRmax (3.1–22.9) and lower ΔF/ (0.28–0.50). Overall values of ΔF/ and maximum quantum yield (Fv/Fm) were generally higher for ice-covered algae. Photosynthetic pigment, C : N and δ13C varied little with irradiance. Diel photosynthetic changes were measured in situ using a custom-built, multi-channel fluorometer. Under sea-ice, ΔF/ of Iridaea mawsonii increased significantly from 0.54 at midday (∼4 µmol photons m−2 s−1) to 0.64 at midnight, despite the relatively low midday irradiance. ΔF/ of ice-free macroalgae also varied significantly over 24 h and between-sample variation exceeded that of under-ice algae. In vivo comparisons of ETR and oxygen evolution of I. mawsonii, Desmarestia menziesii and Himantothallus grandifolius suggested that over 50% of excitation energy was diverted from linear photosynthetic electron flow at Ek; quenching analysis indicated at least partial diversion to non-photochemical quenching (NPQ). During the increasing irradiance of a rapid light curve, values of photochemical quenching (qP) and NPQ of ice-covered algae changed more rapidly than those of open-water algae. Only ice-free H. grandifolius maintained high qP values when exposed to high actinic irradiances (a capacity apparently induced on sea-ice break out), while both ice-free and ice-covered I. mawsonii maintained high NPQ at low actinic irradiances (apparently a constitutive capacity). These attributes help explain the local distribution of macroalgae in the Antarctic, and show strong linkages with the rapid changes in irradiance during sea-ice break-out events.

Photosynthetic electron transport in an anoxygenic photosynthetic bacterium Afifella (Rhodopseudomonas) marina measured using PAM fluorometry.

Blue diode‐based pulse amplitude modulation (PAM) technology can be used to measure the photosynthetic electron transport rate (ETR) in a purple nonsulfur anoxygenic photobacterium, Afifella (Rhodopseudomonas) marina. Rhodopseudomonads have a reaction center light harvesting antenna complex containing an RC‐2 type bacteriochlorophyll a protein (BChl a RC‐2‐LH1) which has a blue absorption peak and variable fluorescence similar to PSII. Absorptance of cells filtered onto glass fiber disks was measured using a blue–diode‐based absorptance meter (Blue‐RAT) so that absolute ETR could be calculated from PAM experiments. Maximum quantum yield (Y) was ≈0.6, decreasing exponentially as irradiance increased. ETR vs irradiance (P vs E) curves fitted the waiting‐in‐line model (ETR = (ETRmax × E/Eopt) × exp(1 − E/Eopt)). Maximum ETR (ETRmax) was ≈1000–2000 μmol e− mg−1 BChl a h−1. Fe2+, bisulfite and thiosulfate act as photosynthetic electron donors. Optimum irradiance was ≈100 μmol m−2 s−1 PPFD even in Afifella grown in sunlight. Quantum efficiencies (α) were ≈0.3–0.4 mol e− mol hλ−1; or ≈11.8 ± 2.9 mol e− mol hλ−1 m2 μg−1 BChl a). An underlying layer of Afifella in a constructed algal/photosynthetic bacterial mat has little effect on the measured ETR of the overlying oxyphotoautotroph (Chlorella).

Depth-specific fluctuations of gene expression and protein abundance modulate the photophysiology in the seagrass Posidonia oceanica

Here we present the results of a multiple organizational level analysis conceived to identify acclimative/adaptive strategies exhibited by the seagrass Posidonia oceanica to the daily fluctuations in the light environment, at contrasting depths. We assessed changes in photophysiological parameters, leaf respiration, pigments, and protein and mRNA expression levels. The results show that the diel oscillations of P. oceanica photophysiological and respiratory responses were related to transcripts and proteins expression of the genes involved in those processes and that there was a response asynchrony between shallow and deep plants probably caused by the strong differences in the light environment. The photochemical pathway of energy use was more effective in shallow plants due to higher light availability, but these plants needed more investment in photoprotection and photorepair, requiring higher translation and protein synthesis than deep plants. The genetic differentiation between deep and shallow stands suggests the existence of locally adapted genotypes to contrasting light environments. The depth-specific diel rhythms of photosynthetic and respiratory processes, from molecular to physiological levels, must be considered in the management and conservation of these key coastal ecosystems.