Soluna Salles

Involvement of solar UV-B radiation in recovery of inhibited photosynthesis in the brown alga Dictyota dichotoma (Hudson) Lamouroux

Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.

Photosynthetic oxygen production and PAM fluorescence in the brown algaPadina pavonica measured in the field under solar radiation

The effects of solar radiation on photosynthetic oxygen production, pulse amplitude-modulated (PAM) fluorescence and pigmentation were measured in the Mediterranean brown macroalgaPadina pavonica (Linnaeus) Lamouroux under field conditions and natural sunlight. Exposure of thalli to solar radiation for 1 h caused a dramatic decrease of their photosynthetic quantum yield, which recovered to initial levels after they had been placed in the shade for 3 h. Photoinhibition also occurred at the natural growth site ofP. pavonica during the hours of maximal solar irradiance. Photosynthetic oxygen production was also affected by high levels of solar radiation both in algae harvested from the surface and from 6 m depth; oxygen production started to decrease after a few minutes of exposure, and negative values were found after 1 h of solar exposure. Chlorophylla content inP. pavonica also decreased during the hours of maximal solar irradiation. These results suggest that photoinhibition ofP. pavonica occurs during part of a typical summer day on Mediterranean coasts.

EFFECTS OF SOLAR RADIATION ON PHOTOSYNTHESIS AND PHOTOINHIBITION IN RED MACROPHYTES FROM AN INTERTIDAL SYSTEM OF SOUTHERN SPAIN

The effects of solar radiation on photosynthesis, chlorophyll content and photoinhibition of the red macrophytes Asparagopsis armata, Gelidium sesquipedale, Plocamium cartilagineum and Feldmannophycus rayssiae from an intertidal system of southern Spain were estimated by means of pulse amplitude modulated fluorometer (PAM), by measurement of the O2 exchange, and by quantification of the chlorophyll content of the thalli. The effective quantum yield ( / ^) decreased in all the experimental organisms after 60 min of exposure to solar radiation; moreover, photoinhibition seemed to be more pronounced and long-lasting in shade-type plants. Secondly, all macrophytes from this study suffered more or less pronounced photoinhibition during some hours of the day at their natural living site. Photoinhibition was maximal around noon and the early afternoon, but almost complete recovery of photosynthesis was achieved by dusk. Similarly, oxygen production and chlorophyll a content were minimal around noon. The ratio (l-qP)/qN was lower in shade than in sun algae indicating a lower electron flow rate, and a lower rate of protective energy dissipation in shade than in sun-grown algae. This ratio is suggested as a good indicator of light stress, to compare different algal species with different pigment content, i. e. sunand shade-type algae.

Relationship between bio-optical characteristics and photoinhibition of phytoplankton

The relationship between the bio-optical properties of different microalgae and photoinhibition after short-term exposure (15 and 30 min) to solar radiation was analyzed. Photoinhibition was determined as the decrease in oxygen production and in the in vivo-induced chlorophyll fluorescence. Microalgae with different chlorophyll concentrations, cell size and volume were used. Both photoinhibition and recovery of oxygen production and quantum yield were higher after 30 than after 15 min exposure to solar radiation. Photoinhibition was reduced when UV-A and UV-B radiations were eliminated from the solar radiation. The decrease of effective quantum yield and oxygen production was not dependent on cell size, biovolume or chlorophyll concentration in the algal cultures. It was, however, related to the bio-optical property of the cultures. manifested as the specific attenuation coefficient (Kc). As a general response, the inhibition of

Pulse amplitude modulated fluorescence in the green macrophytes, Codium adherens, Enteromorpha muscoides, Ulva gigantea and Ulva rigida, from the Atlantic coast of Southern Spain

Abstract The effect of ambient and enhanced solar radiation on the photosynthetic apparatus in four marine green macroalgae on the Southern coast of Spain (Strait of Gibraltar) was investigated using pulse amplitude modulation (PAM) fluorescence. The dependence of the fluorescence parameters on the irradiance of the actinic light was determined for all four species. It showed that maximal fluorescence after light adaptation ( F m ′), photochemical quenching ( q P ) and the photosynthetic quantum yield decreased in Enteromorpha muscoides with irradiance while non-photochemical quenching ( q N ) rose continuously. In Ulva rigida the photosynthetic quantum yield dropped at irradiances above 4 W m −2 but q P did not decrease with increasing light. q N quenching rose sharply above 37 W m −2 , and maximal fluorescence dropped above 1 W m −2 . In Ulva gigantea the yield dropped to zero at irradiances of 37 W m −2 , as did q P at 53 W m −2 . q N started from an intermediate level and increased to a maximum at the highest irradiances. In Codium adherens , the yield and q P behaved similarly as in U. rigida , while q N rose at much lower irradiances. All investigated algae suffered from photoinhibition even at their natural sites of growth when the sun is at high angles. The hypothesis that algae with flat thalli suffer more than those with massive ones was confirmed. Photoinhibition was less pronounced in U. rigida and C. adherens than in the other two species. After 1 h of exposure to solar radiation at the surface, the photosynthetic quantum yield decreased substantially in the surface algae E. muscoides and U. rigida . In both macroalgae, recovery of the photosynthetic quantum yield was almost complete after 2–3 h in the shade. Two other green algae from shaded habitats ( U. gigantea and C. adherens ) did not show complete recovery of the yield from photoinhibition. This confirms the second hypothesis that sun-adapted algae recover faster from photoinhibition than those adapted to shaded sites.

Interactive Effect of UVR and Phosphorus on the Coastal Phytoplankton Community of the Western Mediterranean Sea: Unravelling Eco-Physiological Mechanisms.

Some of the most important effects of global change on coastal marine systems include increasing nutrient inputs and higher levels of ultraviolet radiation (UVR, 280–400 nm), which could affect primary producers, a key trophic link to the functioning of marine food webs. However, interactive effects of both factors on the phytoplankton community have not been assessed for the Mediterranean Sea. An in situ factorial experiment, with two levels of ultraviolet solar radiation (UVR+PAR vs. PAR) and nutrients (control vs. P-enriched), was performed to evaluate single and UVR×P effects on metabolic, enzymatic, stoichiometric and structural phytoplanktonic variables. While most phytoplankton variables were not affected by UVR, dissolved phosphatase (APAEX) and algal P content increased in the presence of UVR, which was interpreted as an acclimation mechanism of algae to oligotrophic marine waters. Synergistic UVR×P interactive effects were positive on photosynthetic variables (i.e., maximal electron transport rate, ETRmax), but negative on primary production and phytoplankton biomass because the pulse of P unmasked the inhibitory effect of UVR. This unmasking effect might be related to greater photodamage caused by an excess of electron flux after a P pulse (higher ETRmax) without an efficient release of carbon as the mechanism to dissipate the reducing power of photosynthetic electron transport.

A new regional algorithm for estimating chlorophyll-a in the Alboran Sea Mediterranean Sea from MODIS-Aqua satellite imagery

ABSTRACT The utility of three different algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS-Aqua is tested in the northern Alboran Sea. The available global algorithm to calculate chlorophyll-a from reflectance of MODIS-Aqua (OC3M) overestimates the surface chlorophyll-a in the study area. Another regional algorithm specifically developed for the Mediterranean Sea (MedOC3) improves the estimates although the best outcome is obtained with OC5, which was developed for Atlantic coastal waters. The three tested algorithms perform worse at in situ chlorophyll-a concentrations higher than 1 mg m−3 and exhibit uncertainty levels higher than 35% for this range of concentrations. A new algorithm (ALBOC3) is proposed which produces a good estimation of the in situ chlorophyll-a for the whole range of concentrations normally registered in the study area (0.1–3.5 mg m−3). We hypothesize that the particular bio-optical features of the northern Alboran Sea phytoplankton explain the poor functioning of the published algorithms that have been tested in this work.

Seasonal changes in the distribution and abundance of marine cladocerans of the Northwest Alboran Sea (Western Mediterranean), Spain

The annual cycle of marine cladocerans was studied over six years from 1994 to 1999 within the frame of the monitoring Project ECOMALAGA at a nine stations in the NW of the Alboran Sea, with the aim of assessing seasonal patterns and interannual trends in distribution and abundance of marine cladocerans. Seven species (Penilia avirostris, Evadne nordmanni, Evadne spinifera, Pseudoevadne tergestina, Pleopis polyphemoides, Podon leuckarti and Podon intermedius) were detected in the northwest Alboran Sea. Total cladoceran relative abundance varied from 0 to 89 % of the total cladocerans. The abundance of cladocerans was higher in summer-autumn than in winter-spring (7012 - 4711.100 and 743 - 217.100m-3 , respectively). The species composition was very different in terms of seasonality. P. polyphemoides, P. leuckarti and P. intermedius appeared mostly during the spring. P. tergestina, E. spinifera and E. nordmanni predominantly occurred during the winter. P. avirostris occurred mostly during the summer and autumn.

Tendencias estacionales y espaciales en la comunidad mesozooplanctónica en una serie temporal plurianual en el noroeste del Mar de Alborán, España

El ciclo anual del mesozooplancton se estudio a lo largo de nueve anos, desde 1992 a 2000, en nueve estaciones ubicadas en el noroeste del Mar de Alboran, con el objetivo de discernir patrones estacionales y tendencias interanuales en la biomasa, composicion y densidad. Las densidades maximas del zooplancton fueron observadas en verano y otono, mientras que los minimos del zooplancton fueron observados en invierno. Los copepodos fueron el grupo mas abundante en invierno, primavera y otono, mientras que en el verano los cladoceros fueron los dominantes seguido por los copepodos. El predominio de cladoceros en verano es basicamente debido a la alta abundancia de Penillia avirrostis. El estudio de tendencias demostro que la abundancia relativa de copepodos aumento en el periodo del estudio, aunque este aumento solamente ha sido significativo en las estaciones occidentales, donde es mas elevada la influencia del agua atlantica. A escala interanual, la biomasa y la densidad registraron una tendencia creciente a lo largo del periodo de muestreo. La diversidad de mesozooplancton mostro una tendencia decreciente. La densidad de Copepoda mostro una disminucion con la temperatura mientras que Cladocera mostro una correlacion positiva. A pesar de estas variaciones interanuales, las distintas fases del ciclo anual y la presencia de varias especies planctonicas fueron notablemente regulares.

New algorithms for estimating chlorophyll-a in the Spanish waters of the Western Mediterranean Sea from multiplatform imagery

ABSTRACT The utility of global and regional algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS (Moderate-Resolution Imaging Spectroradiometer) onboard Aqua and Terra Satellites, SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), MERIS (MEdium Resolution Imaging Spectrometer) and VIIRS (Visible Infrared Imaging Radiometer Suite) is tested in a wide region of the Western Mediterranean Sea, the Spanish Mediterranean. The comparison between chlorophyll-a concentration obtained from samples collected and satellite concentrations calculated with global and regional algorithms for this area demonstrates that satellites overestimate the surface chlorophyll-a. In this work, a set of new algorithms, namely SMED (Spanish MEDiterranean algorithms), are proposed to improve the estimations of surface chlorophyll-a in our study area. The SMED set of algorithms employs the linear function to fit the standard Maximum Band Ratios (MBR) to the in situ surface chlorophyll-a concentration (in logarithmic scale). The implementation of the SMED algorithms is simple, and the accuracy is as good as more complex algorithms like OC5 (5 band algorithms tuned for European Atlantic and tested successfully in the Mediterranean Sea). The improvement of SMED algorithms is important respect to MedOC (built based in data of the Mediterranean Sea) for all sensors, ranging 17%-37% in terms of the coefficient of determination (R2). In the case of OC algorithms (standard global algorithms currently operative for most ocean colour sensors), SMED also improves the estimates in 11%-22%, except in 4% for MERIS. Additionally, when comparing satellite estimates with in situ chlorophyll-a in log-log scale, SMED achieved the best correspondence, even with respect to OC5. During the calibration procedure MERIS remote sensing reflectances (RRS) showed a higher sensitivity to the presence of mineral aerosols, and therefore it is strongly recommended to include the value of Aerosol Optical Thickness (AOT) in the algorithms for chlorophyll in the region under study. A regional algorithm for VIIRS ocean colour sensor is also proposed based on a matchup database built from spatially and temporary distributed SMED chlorophyll-a values of MODIS-Aqua and VIIRS RRS. Our analysis suggests that SeaWiFS, MODIS-Aqua, and VIIRS based SMED algorithms can support generating a multiplatform time series in the region.