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Abstract Globally, the western subarctic Pacific is known as the region with the largest seasonal drawdown in the partial pressure of CO 2 due to biological activity, i.e., high spring primary production and particulate organic carbon flux. These distinctive features are mainly caused by intense spring diatom blooms in coastal Oyashio (COY) and Oyashio (OY) waters. Although phytoplankton assemblages in OY waters are rather well studied, little is known about COY waters. In this study, photophysiological properties and phytoplankton community composition in COY waters were investigated during the pre-bloom and bloom periods from March to April 2015. Next-generation sequencing targeting the 18S rRNA gene revealed that the diatom Thalassiosira generally dominated the phytoplankton community and showed distinct differences in the diatom communities in shelf and offshore waters of the COY. Additionally, the relative contribution of Thalassiosira to the total diatom assemblages showed a positive correlation with maximum photosynthetic rates (P B max) occurring throughout this study. Chlorophyll a concentration and primary productivity were also positively correlated with sea surface temperature, suggesting that temperature was a critical factor for bloom development. Short-term on-deck incubation experiments were carried out to examine the role of temperature in determining planktonic photosynthetic processes. Our results showed an increase in P B max with rising temperature in assemblages from the shelf COY waters. Similarly, transcription levels of the diatom-specific rbcL gene, which encodes the large subunit of RuBisCO, also increased with rising temperature in the shelf assemblages. In contrast, temperature had little effect on the maximum photochemical quantum efficiency (F v / F m) of photosystem II. The results suggested that the transcription activity of the diatom-specific rbcL gene was upregulated by the increase in temperature, and that led to the higher P B max values and the spring diatom bloom in the shelf COY region. [ABSTRACT FROM AUTHOR]

Factors governing phytoplankton community composition and production in tropical estuaries remain mostly unknown. We aimed to quantify phytoplankton biomass, production, and community composition seasonally in 2 tropical estuaries with different levels of nutrient concentrations and turbidity, and we compared them with an offshore control site on the western coast of central Taiwan for two years. Phytoplankton biomass and production varied with season and site. Annual integrated primary production showed that these three sites were mesotrophic systems. Spearman rank correlations showed that phytoplankton biomass and production were positively correlated with water temperature, but negatively correlated with turbidity. The threshold of turbidity was 12 Nephelometric Turbidity Units (NTU), above which phytoplankton chlorophyll a concentrations were <0.5 mg m −3 , and gross production rate was <100 mg C m −3 d −1 . The results of nonmetric multidimensional scaling (MDS) showed that the community was primarily structured by season and secondarily by site. The functional traits further showed that turbidity, water temperature, and SiO 2 concentration were governing factors for the variations in the community. In summary, turbidity was the main factor governing phytoplankton biomass and production, whereas water temperature and SiO 2 concentration had both a direct effect on production and an indirect effect by changing community composition. [ABSTRACT FROM AUTHOR]

Calcifying coralline algae are functionally important in many ecosystems but their existence is now threatened by global climate change. The aim of this study is to improve our understanding of coralline algal metabolic functions and their interactions by assessing the respiration, photosynthesis and calcification rates in an articulated (geniculate) coralline alga,Ellisolandia elongata. Algal samples selected for this case study were collected from an intertidal rock-pool on the coast of Brittany (France). Physiological rates were assessed in summer and winter by measuring the concentration of oxygen, dissolved inorganic carbon and total alkalinity fluxes at five irradiance levels and in the dark using incubation chambers. Respiration, photosynthetic and calcification rates were strongly affected by seasonal changes. Respiration increased with temperature, being ten-fold higher in summer than in winter. Photosynthetic parameters of the photosynthesis-irradiance (P-E) curve,Pgmax, PnmaxandEk, were two- to three-fold higher in summer relative to winter. Photoinhibition was observed under high irradiance indicating an acclimation ofE. elongatato low irradiance levels. Parameters of the calcification-irradiance (G-E) curve,GmaxandEk, were approximately two-fold higher in summer compared with winter. In summer, calcification rates were more strongly inhibited under high irradiance than photosynthetic rates, suggesting a dynamic relationship between these metabolic processes. By inhabiting intertidal rock pools,E. elongataexhibits tolerance to a dynamic physico-chemical environment. Information on respiration, photosynthesis and calcification rates in a calcifying coralline alga inhabiting such dynamic environments in terms of pH and temperature is important in order to better understand how ocean acidification and warming will affect coralline algae in the future. [ABSTRACT FROM AUTHOR]

We investigated the photoacclimation state and photosynthetic rate of cells in the highly eutrophic upper Gulf of Thailand (UGOT), using fast repetition rate (FRR) fluorometry. Observations revealed differences in photosystem II (PSII) parameters: the maximum photochemical quantum efficiency of PSII (Fv/Fm), the functional absorption cross-section of PSII (σPSII) and the rate of reoxidation of the primary PSII electron acceptor (1/τQa), which were dependent on the hydrographic structure of the water column. FRR-derived parameters were used to estimate the chlorophyll a-normalized, photosynthetic rate (PB); the photosynthesis vs. irradiance (P–E) curves were derived from in situ PB profiles. The P–E parameters differed markedly between the upper stratified waters and the mixed water column; that is, the maximum photosynthetic rate $P_{{\rm max}}^{\rm B} $ and the light saturation parameter (Ek) were higher in the upper stratified waters, while the initial slope of the P–E curve (α) was higher in the mixed waters. This indicates that cells acclimated to relatively bright light dominated the upper stratified waters, while cells acclimated to lower light dominated the mixed waters. A significant, positive relationship was found between the average PB in the euphotic zone and surface photosynthetically available radiation, from all profiles at both sampling sites, which suggests that phytoplankton photosynthesis in the UGOT was controlled primarily by irradiance. Furthermore, as stress from nutrient-limitation is unlikely in the UGOT, cells might realize their photosynthetic potential by means of photoacclimation, even under the different light regimes present in the UGOT. [ABSTRACT FROM PUBLISHER]

The article presents a study which investigates the factors that influence the temporal and geographical variations in the photosynthesis of diatoms in the spring bloom in the Western North Pacific Region. It mentions the use of photosynthesis-irradiance (P-E) curve to indicate the relationship of light intensity with the rate of the photosynthetic physiology of phytoplanktons in Oyashio and Transition regions in Hokkaido, Japan. The results show that the rate of photosynthesis is not correlated with light intensity as well as the growth of algae. Meanwhile, the covariation in photosynthesis and light intensity was affected by water temperature.

Abstract: Temporal changes in the abundance, community composition, and photosynthetic physiology of phytoplankton in surface waters were investigated during the second in situ iron (Fe) fertilization experiment in the NW subarctic Pacific (SEEDS-II). Surface chlorophyll a concentration was 0.75mgm−3 on the day before the first Fe enrichment (i.e. Day 0), increased ca. 3-fold until Day 13 after two Fe additions, and thereafter declined with time. The photochemical quantum efficiency (F v/F m) and functional absorption cross-section (σ PSII) of photosystem II for total phytoplankton in surface waters increased and decreased inside the Fe-enriched patch through Day 13, respectively. These results indicate that the photosynthetic physiological condition of the phytoplankton improved after the Fe infusions. However, the maximum F v/F m value of 0.43 and the maximum quantum yield of carbon fixation (φ max) of 0.041molC (molphoton)−1 during the development phase of the bloom were rather low, compared to their theoretical maximum of ca. 0.65 and 0.10molC (molphoton)−1, respectively. Diatoms, which were mainly composed of oceanic species, did not bloom, and autotrophic nanoflagellates such as cryptophytes and prasinophytes became predominant in the phytoplankton community inside the Fe-enriched patch. In ferredoxin/flavodoxin assays for micro-sized (20–200μm in cell length) diatoms, ferredoxin was not detected but flavodoxin expressions consistently occurred with similar levels both inside and outside the Fe-enriched patch, indicating that the large-sized diatoms were stressed by Fe bioavailability inside the Fe-enriched patch even after the Fe enrichments. Our data suggest that the absence of a Fe-induced large-sized diatom bloom could be partly due to their Fe stress throughout SEEDS-II. [Copyright &y& Elsevier]

In Antarctica ozone depletion is highest during spring, coinciding with the reproduction of many seaweed species. Propagules are the life-stage of an alga most susceptible to environmental perturbations. Therefore, fertile thalli of Iridaea cordata (Turner) Bory (Rhodophyta) were collected in the eulittoral of King George Island (Antarctica) to examine spore susceptibility to ultraviolet radiation (UVR). In the laboratory, freshly released tetraspores were exposed to photosynthetically active radiation (PAR) (400–700 nm), PAR+UV-A (320–700 nm) or PAR+UV-A+UV-B (280–700 nm). Photosynthetic efficiency was measured during 1–8 h of exposure and after 48 h of recovery. Additionally, mycosporine-like amino acids (MAAs) and DNA damage were determined. Saturating irradiance of photosynthesis of freshly released tetraspores was 57 µmol photons m−2 s−1. Exposure to increasing fluence of PAR reduced photosynthetic efficiency. UVR further decreased the photosynthetic efficiencies of the tetraspores but spores were able to recover completely after UVR exposure and 2 days post-cultivation under low PAR. DNA damage was minimal and lesions were effectively repaired under photoreactivating light. Concentrations of the MAAs shinorine and palythine were higher in tetraspores treated with UVR than in spores only exposed to PAR. Generally, the tetraspores show a good UV tolerance. This flexible response of the tetraspores of this species to changing radiation conditions enables the alga to grow along a considerable depth gradient from the sublittoral to the eulittoral where they can be exposed to enhanced UVBR under conditions of stratospheric ozone depletion. [ABSTRACT FROM AUTHOR]

This study investigated the variation in the relationship between photosynthesis and ambient light ( P- E curves) for turf algal communities on a temperate reef off the coast of South Australia, analyzing the integrated effects of ambient light and standing biomass. The photophysiology of turfs was studied in situ on a seasonal basis, examining algal communities growing on artificial substrate (plates) at depths of 4 m and 10 m. P- E curves and estimates for the photokinetic parameters ( Pm, Rd, α, Ek, and Ec) were obtained through oxygen evolution methods, using an automated underwater respirometer. Photoacclimation responses to changes in ambient light were strongly affected by the biomass of the community. Pm showed an inverse relationship to standing biomass, irrespective of depth and season, which was considered to be a response to self-shading and boundary layer effects. Biomass effects imposed a high variance on estimates for all photosynthetic parameters, overshadowing differences observed for season and depth. Biomass also affected photoinhibition on turf communities, where significant afternoon depression of photosynthesis was observed in sparse turf patches when compared to denser patches. High areal productivity rates were maintained across all seasons with a significant decrease only being observed during winter. [ABSTRACT FROM AUTHOR]

Biomass of N. spumigena is distributed within the dynamic photic zone that changes in both light quantity and quality. This study was designed to determine whether nutrient status can mitigate the negative impacts of experimental radiation treatments on the photosynthetic performance of N. spumigena. Cyanobacterial suspensions were exposed to radiation consisting of photosynthetically active radiation (PAR=400–700 nm), PAR+UV-A (=PA, 320–700 nm), and PAR+UV-A+UV-B (=PAB, 280–700 nm) under different nutrient media either replete with external dissolved nitrate (N) and orthophosphate (P; designated as +N/+P), replete with P only (−N/+P), or replete with N only (+N/−P). Under low PAR (75 μmol photons m−2 s−1), nutrient status had no significant effect on the photosynthetic performance of N. spumigena in terms of rETRmax, α, and Ek. Nodularia spumigena was able to acclimate to high PAR (300 μmol photons m−2 s−1), with a corresponding increase in rETRmax and Ek. The photosynthetic performance of N. spumigena cultured with supplemental nitrogen was more susceptible to experimental PAR irradiance. Under UVR, P-enrichment in the absence of additional external N (−N/+P) induced lower photoinhibition of photosynthesis compared with +N/−P cultures. However, the induction of NPQ may have provided PSII protection under P-deplete and PAR+UVR conditions. Because N. spumigena are able to fix nitrogen, access to available P can render them less susceptible to photoinhibition, effectively promoting blooms. Under a P-deficient condition, N. spumigena were more susceptible to radiation but were capable of photosynthetic recovery immediately after removal of radiation stress. In the presence of an internal P pool in the Baltic Sea, which may be seasonally available to the diazotrophic cyanobacteria, summer blooms of the resilient N. spumigena will persist. [ABSTRACT FROM AUTHOR]

Haploid tetraspores and diploid carpospores from Antarctic Gigartina skottsbergii were exposed in the laboratory to photosynthetically active radiation (400-700 nm = P), P + ultraviolet (UV)-A radiation (320-700 nm = PA) and P + UV-A + UV-B radiation (280-700 nm = PAB). Photosynthetic performance, DNA damage and repair, spore mortality, and an initial characterization of the UV-absorbing mycosporine-like amino acids (MAAs) were studied. Rapid photosynthesis vs irradiance (E) curves of freshly released spores showed that both tetraspores and carpospores were low-light adapted (Ek = 44 ± 2 and 54 ± 2 mmol photons m-2 s-1, respectively). The light-harvesting and photosynthetic conversion efficiencies were similar (α = 0.13), whereas photosynthetic capacity in terms of optimum quantum yield (Fv/Fm) and relative electron transport rate (rETRmax) were significantly higher in carpospores. Photoinhibition and recovery of photosynthesis were not significantly different between spore ploidy but were significantly affected by radiation and exposure time treatments. Accumulation of DNA damage was UV-B dose dependent and significantly higher in tetraspores than in carpospores. After 2 days postcultivation, DNA lesions were completely repaired in spores exposed to UV-B dose less than 1.2 × 104 J m-2. The dynamic recovery of photosynthetic capacity as well as effective DNA repair mechanism contributed to the relatively low spore mortality (4-14%). A substantial amount of UV-screening MAAs shinorine and palythine were observed for the first time in spores of Gigartinales. This study on stress and physiological characterization of seaweed propagules is important to understand recruitment dynamics and life history phase dominance in the field. [ABSTRACT FROM AUTHOR]

Many laboratories have solely used the Wilson isolate to physiologically characterize the harmful algal bloom (HAB) dinoflagellate Karenia brevis (C. C. Davis) G. Hansen et Moestrup. However, analysis of one isolate may lead to misinterpretations when extrapolating measurements to field populations. In this study, pulse-amplitude-modulated chlorophyll fluorometer (PAM-FL) relative electron transport rate (ETR), F v/ F m, and chl were compared with traditional techniques, such as 14C photosynthesis versus irradiance (P–E) curves, DCMU [3-(3′,4′-dichlorophenyl)-1,1-dimethyl urea] F v/ F m, and extracted chl. The DCMU and PAM-FL values of F v/ F m ( r2 = 0.51) and chl ( r2 = 0.58) were in good agreement. There was no correlation between 14C and PAM-FL α, Pmax, and β parameters because PAM-FL ETR was only a relative measurement. The PAM-FL techniques were then used to investigate P–E curves, quantum yield of PSII ( F v/ F m), and chl from 10 K. brevis isolates to determine whether one or all isolates would better represent the species. Comparisons were made with a radial photosynthetron, which allowed for controlled conditions of light and temperature. Isolate α, Pmax, and β varied between 0.097 and 0.204 μmol e− · m−2 · s−1 · (μmol quanta · m−2 · s−1)−1, 80.41 and 241 μmol e− · m−2 · s−1, and 0.005 and 0.160 μmol e− · m−2 · s−1 · (μmol quanta · m−2 · s−1)−1, respectively. Either carbon limitation and/or bacterial negative feedback were implicated as the cause of the P–E parameter variability. Furthermore, these results directly contradicted some literature suggestions that K. brevis is a low-light-adapted dinoflagellate. Results showed that K. brevis was more than capable of utilizing and surviving in light conditions that may be present on cloudless days off Florida. [ABSTRACT FROM AUTHOR]

The photophysiology of turf algal communities was studied in situ on a temperate reef off the coast of South Australia. Algal communities were grown on artificial substrate at depths of 2, 4, and 10 m. To investigate the response of the algal communities to changing light environments in both the short and long term, reciprocal transplantation experiments were conducted among these depths on a seasonal basis. The extent of photoinhibition was assessed every 3 h for the first 2 days following transplantation and then on a daily basis for 16 days after transplantation. Photosynthetic acclimation was assessed using photosynthesis–light curves obtained from transplanted and non-transplanted turfs after the acclimation period. Transplanted turfs responded very quickly to the light shift. Algae acclimated to low light (10 m depth) were highly susceptible to photoinhibition and photodamage, having greater decreases in maximum and effective quantum yields than turfs from shallower depths. Yield recovery and acclimation usually occurred very rapidly in algae from all depths (3–5 days), but were faster in spring and summer compared with winter. Changes in photosynthetic capacity (across seasons, depths, and after transplantation to a different depth) were accompanied by changes in respiration, so that the ratio of net to gross photosynthetic capacity ( Pmnet : Pmgross) remained high and constant over the whole range of light levels. We discuss the possible acclimation strategies of turfs, taking into account the balance between photoacclimation, production, and growth strategy. [ABSTRACT FROM AUTHOR]

The light-saturated maximum value ( P B max) and initial slope (α) of the photosynthesis-irradiance (P-E) curve were examined in a warm streamer, a cold streamer and a warm core ring off the Sanriku area in the subarctic western North Pacific Ocean during an ADEOS/OCTS Sanriku field campaign in early May 1997. Both P B max and α were within the ranges of temperate populations. A regional difference was apparent in P B max: populations in the warm streamer tended to show higher value ranging between 1.92 and 4.74 mgC (mgChl a)−1h−1 than those in the cold streamer and the warm core ring (1.35–2.87 mgC (mgChl a)−1h−1). A depth variation was also observed in α in both the warm streamer and the warm core ring: shallow populations tended to have lower α than deep populations. The depth variations in both P B max and α resulted in a lower light intensity of the light saturation in a deeper population than that of a shallower one. These depth-related variations in the P-E parameters were likely a manifestation of “shade-adaptation” of photosynthesis. Photoinhibition was not observed over in situ surface light intensity varying below ca 1600 μmol photon m−2s−1. Water-column primary productivity was biooptically estimated to be 233 to 949 mgC m−2d−1 using vertical distributions of the P-E parameters, chlorophyll a, phytoplankton light absorption and underwater irradiance. Applicability of surface data sets for estimation of water-column productivity is discussed. [ABSTRACT FROM AUTHOR]