Fast Repetition Rate Fluorometer Research Articles

Measuring Photophysiology of Attached Stage of Colacium sp. by a Cuvette-Type Fast Repetition Rate Fluorometer.

Fast repetition rate fluorometer (FRRf) is a beneficial method for measuring photosystem II (PSII) photophysiology and primary productivity. Although FRRf can measure PSII absorption cross-section (σPSII), maximum photochemical efficiency (Fv/Fm), effective photochemical efficiency (Fq'/Fm'), and non-photochemical quenching (NPQNSV) for various eukaryotic algae and cyanobacteria, almost all FRRf studies to date have focused on phytoplankton. Here, the protocol describes how to measure PSII photophysiology of an epizoic alga Colacium sp.Ehrenberg 1834 (Euglenophyta), in its attached stage (attached to zooplankton), using cuvette-type FRRf. First, we estimated the effects of substrate zooplankton (Scapholeberis mucronata O.F. Müller 1776, Cladocera, Daphniidae) on baseline fluorescence and σPSII, Fv/Fm, Fq'/Fm', and NPQNSV of planktonic Colacium sp. To validate this methodology, we recorded photophysiology measurements of attached Colacium sp. on S. mucronata and compared these results with its planktonic stage. Representative results showed how the protocol could determine the effects of calcium (Ca) and manganese (Mn) on Colacium sp. photophysiology and identify the various effects of Mn enrichment between attached and planktonic stages. Finally, we discuss the adaptability of this protocol to other periphytic algae.

Diel quenching of Southern Ocean phytoplankton fluorescence is related to iron limitation

Abstract. Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, Fv∕Fm, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ “capacity” of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower Fv∕Fm than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in Fv∕Fm, decreasing as Fv∕Fm increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern–Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders.

Time‐series observations of photosynthetic oxygen production in the subtropical western North Pacific by an underwater profiling buoy system

AbstractWe conducted time‐series observations in the northwestern part of the North Pacific subtropical gyre (30°N, 145°E) from July 2012 to March 2013 using a profiling buoy system equipped with a fast repetition rate fluorometer and dissolved oxygen (DO) sensor in order to understand vertical and temporal variations in gross oxygen production (GOP) by phytoplankton and its contribution to the oxygen cycle in the upper ocean. Under stratified conditions (July–November), daily GOP slightly exceeded 2 mmol O2 m−3 d−1 and only in near‐surface waters. However, during periods of vertical mixing (December–March) when phytoplankton blooms occurred, daily GOP increased in the upper 30 m and often exceeded 5 mmol O2 m−3 d−1. The depth‐integrated daily GOP within the euphotic layer (∫GOPEL) was relatively low (84.0 ± 23.6 mmol O2 m−2 d−1) during stratification, but increased gradually with vertical mixing and reached 460 mmol O2 m−2 d−1 on 17 March 2013. Additionally, during stratified conditions, a subsurface oxygen maximum (SOM) formed below the mixed‐layer depth (MLD) because the steep density gradient constrained upward diffusion of oxygen produced below the MLD. During the period of vertical mixing, the SOM disappeared, and DO concentrations within the upper 100 m increased through both increasing ∫GOPEL and atmospheric oxygen uptake. Using our buoy observations and air–sea gas flux model, we estimated that 24% ± 7% of ∫GOPEL was emitted to the atmosphere during the stratification period, and ∫GOPEL during the mixing period was about 2.4 times the rate of oxygen uptake by the ocean from the atmosphere.

Chlorine toxicity to Navicula pelliculosa and Achnanthes spp. in a flow-through system: The use of immobilised microalgae and variable chlorophyll fluorescence

Chlorination is a widely used antifouling method for freshwater and marine applications. Chlorine added to seawater reacts to form oxidants that are toxic to biofouling organisms. Further, the oxidants that result are short-lived, but may nevertheless affect non-target species in waterbodies receiving the antifouling effluent. This study evaluated the toxicity of chlorinated seawater (e.g. following sodium hypochlorite addition) on two different species of marine benthic diatoms (Achnanthes spp., and Navicula pelliculosa), which are representative of microphytobenthos communities – an important component in coastal habitats that may be exposed to chlorinated seawater. To evaluate the growth inhibition over a 72 h period, algae were immobilised in alginate beads and exposed to different levels of chlorination in a flow through system. Growth rates and physiological condition of the microalgae were evaluated using a Fast Repetition Rate fluorometer (FRRf). To determine whether alginate influenced the sensitivity of algal response, studies were also conducted in a static test system (without renewal of test solutions) using both free cells and immobilised cells with initial chlorine added to achieve a similar range of concentrations as those used in the flow-through study. Within the first hour of the exposure period there was an indication that, for both species, the free algal cells in the static system were more sensitive to exposure to chlorinated seawater than were alginate-immobilised cells in the flow through system. Immobilised cells in a static system with a single addition of chlorine were also less sensitive to chlorination than free algal cells. However, for periods of 24 h or more due to decay of TRO in the static system the exposure of immobilised algae in the flow through system had a greater impact and hence lower effect concentrations. For the flow-through studies Achnanthes spp. was the most sensitive after 72 h exposure with a potential no effect concentration EC10 value of 0.02 mg l−1 as Cl2 equivalents expressed as total residual oxidants (TRO) compared 0.04 mg l−1 TRO for N. pelliculosa. Immobilisation of algal cells in alginate was found to be an effective means of determining the impact of chlorination and is likely to be effective for other non-persistent substances. Based on the data produced, the extent and significance of ecological effects of chlorination upon algal species typical of microphytobenthos are likely to be limited providing discharges comply with a maximum allowable concentration of 0.01 mg l−1 TRO at the edge of an agreed mixing zone.

Physiological response of Prorocentrum lima (Dinophyceae) to varying light intensities.

The benthic dinoflagellate Prorocentrum lima is among the most common toxic morphospecies with a cosmopolitan distribution. This study explored if strains from different environments and different morphotypes, isolated from three locations in the Atlantic Iberian Peninsula and two from the Mediterranean Sea, showed different responses to varying light regimes, after confirming that all strains belonged to the same ribotype. Growth rates and photosynthetic parameters such as Fo, Fv/Fm, and rETRmax were analysed with a Coulter counter, a water-PAM and a fast repetition rate fluorometer. The photosynthetic properties were investigated in a high light stress experiment using strains acclimated to low light (LL) and high light (HL). The highest growth rate was 0.23 day-1 at 80 and 100 μmol photons m-2 s-1 for strains Dn150EHU and Dn60EHU, originated from different locations. Under control conditions (18°C and 90 μmol photons m-2 s-1), growth rate was on average 0.10 day-1. The HL stress exposure induced photodamage to all strains and the recovery period was not sufficiently long for full recovery of Fv/Fm. However, cells acclimated to HL showed a better recovery than the LL acclimated ones. Furthermore, some assumptions are discussed in relation to strains' original location.

Basin-scale spatio-temporal variability and control of phytoplankton photosynthesis in the Baltic Sea: The first multiwavelength fast repetition rate fluorescence study operated on a ship-of-opportunity

This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (Fv/Fm) and functional absorption cross section (σPSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of Fv/Fm and σPSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in Fv/Fm and σPSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σPSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σPSII(593) values were observed later and longer than high σPSII(458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, Fv/Fm variations were similar after excitation at 458nm or 593nm suggesting that the adjustment of Fv/Fm in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.

Effect of biofilm on fluorescence measurements derived from fast repetition rate fluorometers

This study evaluates, for the first time, the influence of biofilms on single and double optical window (SOW and DOW, respectively) fast repetition rate fluorometer (FRRF) measurements of microalgal photosystem-II initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv = Fm – F0), quantum yield (Fv/Fm) and functional absorption cross section (σPSII)]. Biofilms with chlorophyll > 0.1 μg cm−2 and > 0.3 μgcm−2 on SOW and DOW, respectively, produced a substantial increase in fluorescence. However, the relative magnitude of biofouling effects depended on sample chlorophyll concentrations, being more critical at concentrations < 1 mg m−3. In DOW-FRRF, biofilms affected F0 (increased) and Fv/Fm (decreased) but not Fv and σPSII, whereas in SOW-FRRF, biofilms increased fluorescence and showed a variable effect on Fv/Fm and σPSII, because only biofilms on SOW attained actual Fm. As a result, the biofilm effect was substantial on SOW-FRRF measurements. On the other hand, the neutral-density filters (representing non-chlorophyll containing biofilms) with different transmission levels reduced the fluorescence signal. Correction procedures for the above photosystem-II parameters are proposed here.

Performance of Fast Repetition Rate fluorometry based estimates of primary productivity in coastal waters

Capturing the variability of primary productivity in highly dynamic coastal ecosystems remains a major challenge to marine scientists. To test the suitability of Fast Repetition Rate fluorometry (FRRf) for rapid assessment of primary productivity in estuarine and coastal locations, we conducted a series of paired analyses estimating 14 C carbon fixation and primary productivity from electron transport rates with a Fast Repetition Rate fluorometer MkII , from waters on the Australian east coast. Samples were collected from two locations with contrasting optical properties and we compared the relative magnitude of photosynthetic traits, such as the maximum rate of photosynthesis ( P max ), light utilisation efficiency (α) and minimum saturating irradiance ( E K ) estimated using both methods. In the case of FRRf, we applied recent algorithm developments that enabled electron transport rates to be determined free from the need for assumed constants, as in most previous studies. Differences in the concentration and relative proportion of optically active substances at the two locations were evident in the contrasting attenuation of PAR (400–700 nm), blue (431 nm), green (531 nm) and red (669 nm) wavelengths. FRRF-derived estimates of photosynthetic parameters were positively correlated with independent estimates of 14 C carbon fixation ( P max : n = 19, R 2 = 0.66; α: n = 21, R 2 = 0.77; E K : n = 19, R 2 = 0.45; all p < 0.05), however primary productivity was frequently underestimated by the FRRf method. Up to 81% of the variation in the relationship between FRRf and 14 C estimates was explained by the presence of pico-cyanobacteria and chlorophyll- a biomass, and the proportion of photoprotective pigments, that appeared to be linked to turbidity. We discuss the potential importance of cyanobacteria in influencing the underestimations of FRRf productivity and steps to overcome this potential limitation. • We assessed primary productivity in coastal waters using fluorometry (FRRf) and 14 C. • FRRf estimates of P max , α and E K were strongly correlated with 14 C estimates. • Primary productivity was underestimated by the Chl- a fluorescence method. • Cyanobacteria were important in driving variability between FRRf and 14 C estimates.

NITROGEN FIXATION, HYDROGEN CYCLING, AND ELECTRON TRANSPORT KINETICS IN TRICHODESMIUM ERYTHRAEUM (CYANOBACTERIA) STRAIN IMS101(1).

This study describes the relationships between dinitrogen (N2 ) fixation, dihydrogen (H2 ) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H2 produced:N2 fixed (H2 :N2 ) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 μmol photons · m(-2) · s(-1) , the rate of N2 fixation, as measured by acetylene reduction, saturated at light intensities of 200 μmol photons · m(-2) · s(-1) . In contrast, net H2 production continued to increase with light levels up to 1,000 μmol photons · m(-2) · s(-1) . The H2 :N2 ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N2 fixation and net H2 production, while the H2 :N2 ratio increased with increasing level of PQ pool reduction. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N2 fixation and H2 cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H2 :N2 ratio and modulate net H2 production.

Phytoplankton productivity in the western subarctic gyre of the North Pacific in early summer 2006

We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m−2 in the middle of June and remained in the 30–40 mg Chl a m−2 range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m−2 day−1 and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface ocean in the western subarctic Pacific.

Monitoring copper toxicity in natural phytoplankton assemblages: application of Fast Repetition Rate fluorometry

Four experiments were conducted with natural coastal phytoplankton assemblages exposed to [Cu] within the range 5–80μgL−1. The effect of Cu on several biological variables such as chlorophyll a concentration, particle size distribution, O2-production and fluorescence variables recorded by a Fast Repetition Rate fluorometer was monitored during 72h. Variable fluorescence (Fv) was the most sensitive and rapid among all the variables tested. This work contributes to reinforce the use of fluorescence endpoints in ecotoxicological studies by proving their ecological relevance through relationships found between fluorescence and population-level responses as growth rate and gross O2 production. The lowest calculated EC10 was 2.65μgL−1, concentration commonly exceeded in polluted waters.

Use of fluorimetry to evaluate atrazine toxicity to phytoplankton communities

Toxicity of atrazine was determined for natural phytoplankton communities in lake water samples from Missisquoi Bay (Lake Champlain, CA, US) at monthly intervals from May to August 2005 in order to assess how this herbicide could affect phytoplankton dynamics. Atrazine was added at 0, 5, 20, and 50 μ g L− 1 in 14 L treatments and incubated under simulated ambient light conditions (43 μ mol m− 2 s− 1). Phytoplankton community composition changes in the treatments were followed using a phytoplankton-specific fluorometer (FluoroProbe) and size fractionated filtration and analysis of extracted chlorophyll-a. Phycocyanin-rich Cyanobacteria decreased with increasing atrazine concentration in June and July and increased with atrazine concentration in August. Further experimentation utilizing a fast repetition rate fluorometer revealed that atrazine impacts on phytoplankton autofluorescence can impair FluoroProbe measurements over the short term (1 h to &amp;lt; 7 days).

Assessment of carbon- and fluorescence-based primary productivity in Ariake Bay, southwestern Japan

A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by 13C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r 2 > 0.90) and daily (r 2 = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. 13C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to 13C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate ( P B ) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR– P B relationship) was found to be linear for FRRF and curvilinear for 13C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR– P B relationships, a combined and/or instantaneous PAR– P B relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF.

Use of Fast Repetition Rate Fluorometry on Detection and Assessment of PAH Toxicity on Microalgae

Cultures of the flagellate Isochrysis galbana were used to carry out the ecotoxicological evaluation of four PAHs [(naphthalene, phenanthrene, pyrene (Pyr) and fluoranthene (Flu)] by monitoring growth rate and the fluorescence variables F 0, F m, F v and F v/F m, determined with a fast repetition rate fluorometer. The results presented in this investigation showed that F v was a suitable endpoint in acute ecotoxicological tests with marine phytoplankton. The derived effective concentrations followed the known narcotic mechanism of toxicity and showed sensitivity levels comparable to marine invertebrate embryo-larval bioassays. Pyr and Flu showed the lowest EC10, which ranged between 168–279 and 189–697 nM, respectively.

In situ diel cycles of photosynthesis and calcification in hermatypic corals

Diel cycles of photosynthesis, respiration, and calcification were studied in situ on two hermatypic corals, Acropora eurystoma and Favia favus, using a submerged respirometer deployed at 5‐m depth in the Gulf of Eilat, Israel. A fast‐repetition‐rate fluorometer (FRRF) was placed in front of one coral in each incubation. Net photosynthesis (PN) and calcification were positively correlated with photosynthetically available radiation (PAR). A hysteresis phenomenon occurred in both photosynthesis and calcification relative to PAR: rates were higher in the afternoon than in the morning. This hysteresis is reversed (counterclockwise) compared to that observed in other photosynthetic organisms (plants and algae); however, the quantum yield (∆F′ : Fm′) and the rate of photosynthetic electron transport per PSII reaction center (Pf) showed a regular (clockwise) hysteresis. The photosynthetic compensation point (Ic) was significantly higher in the morning than in the afternoon, ~900 and ~300 µmol photons m−2 s−1, respectively. We suggest that PN, reversed hysteresis, and lower morning compensation points are caused by higher respiration in the morning than in the afternoon. This may be a result of higher predation rates by the corals during the night, when plankton is more abundant, followed by higher respiration during the digestion of the prey. Calcification counterclockwise hysteresis was observed during high‐PAR periods (&gt;400 and 200 µmol photons m−2 s−1 for A. eurystoma and F. favus, respectively). We suggest that high morning respiration may induce a decrease in internal tissue pH, causing lower calcification rates.

Estimating phytoplankton primary production in Lake IJsselmeer (The Netherlands) using variable fluorescence (PAM-FRRF) and C-uptake techniques

In this paper we compare measured rates of C-fixation obtained using in situ deployment of a fast repetition rate fluorometer (FRRF) applying two different calculation protocols and a waterPAM fluorometer. The measurements were carried out in the large, shallow Lake IJsselmeer (The Netherlands). Turbidity appears to be the most important factor in explaining photosynthetic parameters. Non-photochemical quenching (NPQ) in the antenna was observed, and the degree of NPQ was positively correlated with the irradiance and mixing conditions. However, NPQ did not affect the functional cross-section. Conversion of photosynthetic electron transport rates (ETR) into rates of carbon fixation requires knowledge of two or three parameters (depending on the protocol and instrument used) to calculate C-fixation from ETR: the electron yield (Φe, i.e. the reciprocal of the quantum requirement of PSII), the photosynthetic quotient (PQ) and the number of PSII (nPSII). Using normally assumed values for these three parameters resulted in overestimation of the measured rate of C-fixation but, in all cases, ETR was linearly related to it. The degree of overestimation was rather constant, despite considerable changes in phytoplankton composition. Spectral correction of fluorescence data caused a reduction of 30% or an increase of 44% in the estimated C-fixation, depending how C-fixation was estimated. We describe a method that allows estimation of the Φe/PQ ratio based on a comparison of the quantum efficiencies for C-fixation and PSII and show that, with a single and realistic value for this ratio, primary production could be accurately predicted at different times of the year.

Photosynthetic community responses to upwelling in mesoscale eddies in the subtropical North Atlantic and Pacific Oceans

In this paper we summarise the photo-physiological responses of phytoplankton to upwelling of macronutrients in mesoscale eddies in the subtropical North Atlantic (EDDIES project, Sargasso Sea) and subtropical North Pacific (E-FLUX project, Hawaii). The observations, obtained on two sets of cruises over 2 years, occupied six cyclonic eddies and two mode-water eddies. The photosynthetic physiological parameters were measured using a bench-top fluorescence induction and relaxation (FIRe) system and a submersible in situ fast repetition rate fluorometer (FRRF) deployed on an undulating towed vehicle. Both of these instruments were used to provide highly sensitive and well-resolved data on community responses. The responses are dependent on both the type of eddy and its stage of development. Our results indicate that, while cyclonic eddies in the Atlantic and Pacific can increase primary photosynthetic production early in their development, mode-water eddies in the subtropical North Atlantic can support patchy blooms of large diatoms for long periods of time (more than 3 months).

In situ observation of phytoplankton productivity by an underwater profiling buoy system: use of fast repetition rate fluorometry

To gain a better understanding of variability in phytoplankton productivity in the oceans, we developed an underwater profiling buoy system that uses a fast repetition rate (FRR) fluorometer. We used the profiling buoy system to observe phytoplankton productivity in Sagami Bay, Japan, from 15 April to 10 May 2005. During the observation period, chlorophyll a (chl a) con- centration increased gradually, peaking at > 5 mg chl a m -3 at a depth of 10 m, indicating the occur- rence of phytoplankton blooms. Gross oxygen production (PO2), as determined by FRR fluorometry, increased with the development of phytoplankton blooms and peaked at 49.4 mmol O2 m -2 h -1 on 2 May 2005, when both the chl a concentration and surface irradiance were high. To validate FRR- based PO2, the light-utilization efficiency of a water column (ψO2) was calculated and compared with previous values determined for this location by the oxygen evolution method. The ψO2 derived from FRR fluorometry showed good agreement with those by the oxygen evolution method, suggesting that FRR fluorometry was able to roughly estimate in situ daily PO2. Our profiling buoy system has potential benefits for the measurement of oceanic phytoplankton productivity at a high resolution.

Artifacts in measurements of chlorophyll fluorescence transients, with specific application to fast repetition rate fluorometry

A theoretical framework was developed to describe how instrument and sample artifacts affect measurements of variable fluorescence transients in phytoplankton. This framework identified the proper procedure for correcting for common artifacts in the transients measured with a widely used instrument, the Fasttracka fast repetition rate fluorometer. The impulse response of this fluorometer can be substantial, requiring correction for a dynamic instrument artifact in addition to the static artifacts that can be assessed using traditional “blanks.” In a low‐biomass region of the North Pacific, approximately one‐third of the fluorescence transient measured with this instrument represented such artifacts. Correcting for these using filtered seawater blanks only, and not accounting for the instrument's own response, failed to remove errors as high as 22% in estimates in the photochemical yield and as much as −16% to +22% in estimates of the functional cross section of Photosystem II. This analytical framework and the corrective procedure are generalized and can be used to determine how a wide range of artifacts affect measured variable fluorescence transients, including those characteristic of fluorometers other than the Fasttracka or those more relevant in meso‐ or eutrophic regions of the ocean.

Differences in photosynthetic activity between coral sections infested and not infested by boring spionid polychaetes

A SCUBA-based fast repetition rate fluorometer (FRRF) was used to study differences in the functional absorption cross-section of Photosystem II (σPSII) between areas of a coral colony of Astreoporamyriophthalma that were infested with spionid polychaetes vs areas lacking worms. The mean value of σPSII in infested areas (mean±SD=347.62±30.67 Å2) was significantly higher than in the areas that were not infested (316.32±17.49 Å2; P&lt;0.0001). Several physiological mechanisms are discussed that may contribute to the observed differences.