Ana Bartual

Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

Abstract The morphological and physiological differences between two morphotypes of Z. noltii Hornem. were studied in the intertidal meadows on the south-western Iberian Peninsula (Palmones river estuary and Ria Formosa). A small-leaved morphotype (SM) grows mainly at high intertidal sites, meadow edges or in recently deposited sandbanks, whereas a large-leaved morphotype (LM) generally thrives in well-structured beds or in deeper places. This study deals with the morphological, biochemical and physiological differences between these morphotypes as well as the ecological implications of the occurrence of different morphotypes in the same meadow. Shoot length, leaf width, rhizome internode length, roots per node, root length, leaf nutrient and pigment contents, and photosynthetic rates of both morphotypes were compared. The below-ground architecture (root and rhizome complex) of both morphotypes was more developed in sites characterized by higher hydrodynamics and/or a lower nitrogen content in sediments. Both morphotypes showed similar values for photosynthetic efficiency, dark respiration rate and compensation irradiance. On the other hand, the net photosynthetic capacity was much greater (5-fold) for the SM. This difference could explain the greater growth rate and faster leaf turnover rate of the SM compared with the LM. The occurrence of the SM in newly settled areas (and in the meadow edges) could be explained on the basis of its higher growth rate, which would allow a faster spreading of the meadow and/or better recovery after burial resulting from stormy weathers.

Physiological and Molecular Evidence that Environmental Changes Elicit Morphological Interconversion in the Model Diatom Phaeodactylum tricornutum

Over the last decades Phaeodactylum tricornutum has become a model to study diatom biology at the molecular level. Cells have the peculiarity to be pleiomorphic and it is thought that this character is triggered by culture conditions, although few quantitative studies have been performed and nothing is known at the molecular level. Our aim was to quantify the effect of growth conditions on cell morphology of different P. tricornutum strains by quantitative microscopy, cellular imaging, and non-targeted transcriptomics. We show that morphotype changes can be regulated by changing culture conditions, depending on the strain, and show a common trend of increased oval cell abundance as a response to stress. Examination of expressed sequence tags (ESTs) from triradiate cells infers the importance of osmoregulation in the maintenance of this morphotype, whereas ESTs derived from oval cells grown in hyposaline and low temperature conditions show a predominance of genes encoding typical components of stress pathways, especially in signaling, cell homeostasis and lipid metabolism. This work contributes to better understand the importance of the unique capability of morphotype conversion in P. tricornutum and its relevance in acclimation to changing environmental conditions.

Surface distribution of chlorophyll, particles and gelbstoff in the Atlantic jet of the Alboran Sea: from submesoscale to subinertial scales of variability

The surface distribution of light attenuation due to particles (c) as well as chlorophyll-a and gelbstoff fluorescence (Fch and Fcd, respectively) were recorded during an OMEGA (EU funded, MAST III project) cruise in the northwestern Alboran Sea through a high spatial (zonally separated by 10 km and virtually meridionally continuous) and temporal (about 3 days between each of the three repeated surveys made in the zone) resolution sampling design. The distributions obtained for these variables were tightly linked to the physical forcing at the different scales that the sampling design was able to resolve. Low values dominate the quasi permanent anticyclonic gyre occupying the western Alboran Sea, whereas the frontal zone directly affected by the entrance of the Atlantic jet depicts much higher records for c, Fch and Fcd. High geostrophic Froude numbers in the jet, and the subsequent increase in turbulence diffusion of nutrients towards the surface, cannot alone justify this spatial distribution. Instead, high phytoplankton concentration at the jet could also result from the entrainment and advection of water from the upwelling zone at the Spanish coast. However, T–S characteristics suggest that this is neither the most important process for the biological enrichment of the jet, so that other mechanisms such as vertical ageostrophic velocities at the edge of the gyre must also be considered. Due to the time needed for phytoplankton growth, the intense horizontal velocities associated to the jet can decouple the sectors where deep nutrient-rich waters reach the surface from sectors where high values of the recorded variables are observed. The decoupling hinders a differentiation of this fertilization mechanism from other possible alternatives as mixing at the sills in the Strait of Gibraltar. In the third survey, the spatial structure of surface warm waters in the gyre and cold waters in the front became less apparent. ADCP data show a southward migration of the jet in a fluctuation probably related to transient states in the Atlantic jet and western Alboran gyre system. The qualitative response of c, Fch and Fcd to these scales of variability was very similar and close to the changes observed in temperature. However, the values of Fcd varied in a much narrower range than c or Fch (a factor of 2 and 10, respectively), which indicates a distinct control for the abundance of Gelbstoff. This control dumps the range of variability in the western Alboran and its origin is discussed in the context of photobleaching or bacterial degradation of these substances.

Ring test for whole-sediment toxicity assay with a benthic marine diatom

This work presents the results of an interlaboratory proficiency exercise for whole-sediment toxicity assays with the benthic marine diatom Cylindrotheca closterium. An assay protocol was established and followed by all participating laboratories. Cell growth after 72 h exposure was the endpoint used. Four sediment samples of unknown toxicity were assayed. The main problem encountered during this exercise was the differences in the cell growth of algae exposed to reference sediment. Those differences may be associated with changes in the physiological status of the initial culture due to temperature changes during transport to the other laboratories. In general, the method proposed presented good replicability (precision between replicates) and reproducibility (interlaboratory precision). Around 80% (17 out of 21) of results obtained were classified as satisfactory (Z-scores <2). The whole-sediment assay with C. closterium presented here can be considered sufficiently successful for possible use as a standard toxicity test. The assay is simple to perform, the proposed species is ecologically relevant as an integral component of microphytobenthos, and is widely distributed around the world. These positive factors suggest that the whole-sediment assay with the benthic marine diatom C. closterium can be used as a reliable tool in marine sediment quality assessment.

Growth and Biochemical Composition of the Diatom Phaeodactylum tricornutum at Different pH and Inorganic Carbon Levels under Saturating and Subsaturating Light Regimes

Abstract The effects of pH and total dissolved inorganic carbon (DIC) availability on the growth and biochemical composition of Phaeodactylum tricornutum Bohlin acclimated to restricted and saturated light conditions have been investigated. Diluted, unbuffered and nutrient enriched batch cultures were grown at several pHs (different [CO2( aq )] for the same DIC) and various DIC conditions (different [CO2( aq )] for an equal pH) under saturating (150 μmol m−2 s−1) and subsaturating (30 μmol m−2 s−1) light levels. The growth rate was unaffected by pH treatments at saturating light. In contrast, under subsaturating light conditions, the growth rate was significantly reduced at pHs over 8.5 and also at low DIC levels to a similar extent. Biochemical composition revealed that the growth rate was limited by different resources. At natural DIC (DIC = 2.1 mM) and low light conditions, there was an increase of the C:N ratio under high pH (low [CO2( aq )]) associated with a reduction of nitrogen, chlorophyll a and total protein content, resembling the biochemical composition of a diatom cultured under nitrogen limitation. On the contrary, under low light and low DIC conditions, in which both [CO2( aq )] and [HCO3 −] are reduced, cellular carbon content decreased for a relatively constant nitrogen content, decreasing the C:N ratio. The results are discussed in terms of competition between carbon and nitrogen metabolism for energy, and showed that the imposition of different [CO2( aq )] by changing pH or DIC levels of seawater affected in different ways the final biochemical composition of Phaeodactylum tricornutum.

Polyunsaturated aldehydes from large phytoplankton of the Atlantic Ocean surface (42°n to 33°s).

Polyunsaturated aldehydes (PUAs) are organic compounds mainly produced by diatoms, after cell wounding. These compounds are increasingly reported as teratogenic for species of grazers and deleterious for phytoplanktonic species, but there is still scarce information regarding concentration ranges and the composition of PUAs in the open ocean. In this study, we analyzed the spatial distribution and the type of aldehydes produced by the large-sized (>10 μm) phytoplankton in the Atlantic Ocean surface. Analyses were conducted on PUAs released after mechanical disruption of the phytoplankton cells, referred to here as potential PUAs (pPUAs). Results show the ubiquitous presence of pPUA in the open ocean, including upwelling areas, as well as oligotrophic gyres. Total pPUA concentrations ranged from zero to 4.18 pmol from cells in 1 L. Identified PUAs were heptadienal, octadienal and decadienal, with heptadienal being the most common (79% of total stations). PUA amount and composition across the Atlantic Ocean was mainly related to the nitrogen:phosphorus ratio, suggesting nutrient-driven mechanisms of PUA production. Extending the range of trophic conditions considered by adding data reported for productive coastal waters, we found a pattern of PUA variation in relation to trophic status.

Potential polyunsaturated aldehydes in the Strait of Gibraltar under two tidal regimes.

Diatoms, a major component of the large-sized phytoplankton, are able to produce and release polyunsaturated aldehydes after cell disruption (potential PUAs or pPUA). These organisms are dominant in the large phytoplankton fraction (>10 µm) in the Strait of Gibraltar, the only connection between the Mediterranean Sea and the Atlantic Ocean. In this area, the hydrodynamics exerts a strong control on the composition and physiological state of the phytoplankton. This environment offers a great opportunity to analyze and compare the little known distribution of larger sized PUA producers in nature and, moreover, to study how environmental variables could affect the ranges and potential distribution of these compounds. Our results showed that, at both tidal regimes studied (Spring and Neap tides), diatoms in the Strait of Gibraltar are able to produce three aldehydes: Heptadienal, Octadienal and Decadienal, with a significant dominance of Decadienal production. The PUA released by mechanical cell disruption of large-sized collected cells (pPUA) ranged from 0.01 to 12.3 pmol from cells in 1 L, and from 0.1 to 9.8 fmol cell−1. Tidal regime affected the abundance, distribution and the level of physiological stress of diatoms in the Strait. During Spring tides, diatoms were more abundant, usually grouped nearer the coastal basin and showed less physiological stress than during Neap tides. Our results suggest a significant general increase in the pPUA productivity with increasing physiological stress for the cell also significantly associated to low nitrate availability.

Temperature differentially affects the persistence of polyunsaturated aldehydes in seawater

Environmental context Diatoms, unicellular algae that live suspended in the water column, can undergo periods of rapid growth, called blooms. When these algal blooms die, organic compounds including polyunsaturated aldehydes are released to the surrounding water with currently unknown ecological effects. Here we demonstrate that temperature differentially affects the persistence of three major polyunsaturated aldehydes produced by diatoms, and we quantify the removal rates from seawater of these compounds. Abstract Polyunsaturated aldehydes (PUAs) are volatile compounds commonly released into the environment by different fresh and seawater phytoplankton species. Diatoms are among the main producers of these metabolites in seawater. The release of these metabolites in seawater is known to be wound-activated as a consequence of predation or cell lysis. Hence, the interaction of phytoplankton species that produce PUAs with other marine organisms is being thoroughly investigated. However, the stability of these compounds in seaweater once they are released and their persistence under different environmental conditions have never been quantified. In this work, we reveal an important effect of seawater temperature on the persistence of dissolved 2E,4E/Z-decadienal (DECA), 2E,4E/Z-octadienal (OCTA) and 2E,4E/Z-heptadienal (HEPTA) in seawater at the nanomolar scale. These three aldehydes were more persistent at 10°C than at either 15 or 20°C. Half lives of OCTA and HEPTA were reduced from 200h at 10°C to 80h at 15°C and 60h at 20°C. In addition, DECA was consistently more persistent than OCTA and HEPTA at the three temperatures assayed. This dependence of the persistence of dissolved PUAs on seawater temperature could determine a differential effect of equivalent PUA concentrations on the diversity and plankton community’s structure at different water depths, seasons or latitudes.

Phenotypic response of the diatom Phaeodactylum tricornutum Bohlin to experimental changes in the inorganic carbon system

The physiology and biochemistry of Phaeodactylum tricornutum have been extensively studied, and some aspects of its biology are well known. Phenotypic plasticity is probably one of its most remarkable features. Two basic morphotypes, fusiform and triradiate, can be found in natural liquid environments. Although the transformation from one morphotype to the other has been previously reported, ecological causes and consequences of such transformation remain unknown. Here, we report changes in the relative abundance of the two morphotypes of Phaeodactylum associated with changes in the inorganic carbon system. The relative abundance of the triradiate morphotype increased in cultures grown at either high pH or high dissolved inorganic carbon, and markedly so under subsaturating illumination for growth. At high pH, this increase was strongly correlated with a decrease in the overall culture growth rate. At the individual (cell) level, there was a larger increase in the surface area of the triradiate morphotype (resulting in a higher surface-to-volume ratio) than in the fusiform morph under subsaturating illumination for growth. These results provide new insights into the biology of this diatom, mainly related to the performance (fitness) of the two basic morphotypes under contrasting illumination for growth and different inorganic carbon conditions.

Enhancement of photosynthesis in post-disturbance resprouts of two co-occurring Mediterranean Erica species

The higher growth rates of resprouting shoots compared with those of mature plants in resprouter woody species are supported by higher rates of photosynthesis and transpiration. In this contribution we hypothesize that species with higher resprouting vigour will show a larger enhancement of photosynthesis in resprouting shoots. We test this hypothesis by comparing gas exchange and leaf parameters between resprouting and mature plants in Erica scoparia and E. australis. These two Erica species co-occur in Mediterranean heathlands of the Strait of Gibraltar. Erica scoparia has a higher rate of post-disturbance starch recovery than E. australis, which makes it more resistant to recurrent disturbance. We tested the hypothesis that enhancement of photosynthesis and water use characteristics of resprouting shoots compared with mature plants should be more pronounced in E. scoparia. In both species, resprouts had higher efficiency in the use of light and higher maximum net photosynthesis than mature shoots. However, contrary to expectations, differences in the photosynthetic performance between resprouts and mature plant shoots were larger in E. australis. Higher root to shoot ratios in resprouting E. australis plants, determined by their slower above-ground recovery, together with stronger demand from carbon sinks might explain this result.