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  • 1
    Electronic Resource
    Electronic Resource
    Photo-inhibition and seasonal photosynthetic performance of the seaweed Laminaria saccharina during a simulated tidal cycle: chlorophyll fluorescence measurements and pigment analysis (2002)
    Oxford, UK : Blackwell Science, Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Laminaria saccharina (Lamouroux) form the largest, most abundant and conspicuous seaweed populations along the French coast of the eastern English Channel. As they are located in the intertidal zone, they are exposed to considerable irradiance variations, mainly related to tidal cycles. The response of these macro-algae to light variations over a simulated daily tidal cycle was investigated in the laboratory during spring, autumn and winter using chlorophyll fluorescence and pigment analysis. The maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm) and the operating PSII efficiency (ΦPSII) showed clear daily cycles according to the irradiance variation throughout the 12 h simulated tidal cycle, whereas the pattern of the relative photosynthetic electron transport rate (rETR) was not so obvious. The algae reacted to the light increase by developing photoprotective mechanisms able to dissipate the excess energy reaching PSII by the de-epoxidation of violaxanthin into zeaxanthin. Because of their better acclimation to strong irradiance, spring populations were less affected by this light treatment than were winter populations. In particular, L. saccharina showed more pigments of the xanthophyll cycle in spring to cope with strong irradiance exposure. Alternatively, they developed their antenna complexes in winter to harvest a maximum of light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00869.x
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon-dioxide production and metabolic parameters in the ophiurid Ophiothrix fragilis (1997)
    Springer
    Marine biology 127 (1997), S. 699-704 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract As part of the evaluation of fluxes between the water column and a rich benthic community of the Dover Strait (Eastern English Channel), laboratory measurements of oxygen consumption were carried out on a common ophiurid, Ophiothrix fragilis (Abildgaard), from February 1993 to February 1995. The mean O2-consumption rate was evaluated at 0.31 mg O2 g−1 h−1 (ash-free dry weight). Simultaneous measurements of O2 consumption and CO2 production using the pH-alkalinity method revealed an average respiratory quotient of 0.69 proved suitable for converting oxygen demand to carbon flux. A seasonal trend in respiration data was demonstrated by sinusoidal curves fitted to O2-uptake and CO2-release data as a function of time. The influence on respiration rate of two seasonal parameters (temperature and food availability) is discussed; linear regression indicated a highly significant relationship between O2 consumption (or CO2 production) and temperature; both O2-consumption and CO2-production rates decreased with starvation. The average O:N ratio was estimated at 8.46, close to the theoretical value when proteins constitute the catabolic substrate. The annual carbon respired by the O. fragilis community examined and the estimated annual primary production by phytoplankton indicate that the respiration of the O. fragilis community could supply 35% of phytoplankton carbon requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050060
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  • 3
    Electronic Resource
    Electronic Resource
    Ammonium excretion by the ophiuridOphiothrix fragilis as a function of season and tide (1991)
    Springer
    Marine biology 111 (1991), S. 425-429 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ammonium excretion of a dense population (~1 500 individuals m−2) of the ophiuridOphiothrix fragilis (Abildgaard) was measured in the Dover Straits (French coast) between May 1989 and March 1990: the excretion rate varied from 4.8 µg N g−1 dry wt h−1 in November to 12.8 µg N g−1 dry wt h−1 in June. Mean individual ammonium excretion,E, wasE=0.019⋅t +1.26 (whereE=µg N individual−1 andt=time in min;r=0.80;N=81). Variations in the ammonium excretion rate during a tidal cycle appeared to arise from variations in the duration of the suspension-feeding activity ofO. fragilis, which was governed by the strength of the tidal current. During short-term starvation, excretion was low (E=0.009⋅t+1.47;r=0.91;N=17), increasing with increasing length of starvation [E=4.62⋅lnt−2.5;r=0.95;N=17], as observed for other echinoderms; this could be due to catabolism of tissue. The daily ammonia flux from thisO. fragilis population to the water column was estimated at 41 mg N m−2 d−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319414
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  • 4
    Electronic Resource
    Electronic Resource
    Multi-scale heterogeneity in a macrobenthic epifauna community (1995)
    Springer
    Hydrobiologia 300-301 (1995), S. 375-381 
    Details
    ISSN: 1573-5117
    Keywords: benthos ; multi-scale heterogeneity ; biomass ; scuba diving ; sampling strategy ; suspension-feeders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A quantitative study, based on monthly samples taken by divers with 0.1m2 quadrats, was conducted on a benthic community settling coarse sediments in an area exposed to strong water currents. The richness of the community was high both in terms of biomass (270±107 g m−2 in ash-free dry weight) and diversity (ten zoologicals groups for a total of 98 species). Three suspension feeding species were dominant: Ophiothrix fragilis, Urticina felina and Alcyonium digitatum accounted for more than 95% of the total biomass at all sampling periods. Spatial heterogeneity analysis confirmed the role of these three dominant species. Heterogeneity revealed at a scale of 0.1 m2 by dendrograms (qualitative similarity index) or by Factor Correspondence Analysis (FCA) (on biomasses) was due to the strong dispersion of rare species. The influence of the observation scale was visualised by building Rank-Frequency Diagrams using progressively aggregated replicates. The distribution of relative biomasses and the rank of the dominant species always stabilized at scale of 0.4 or 0.5 m2. The three dominant species were overdispersed at a scale of 0.1 m2 compared with a Poisson distribution. Spatial competition among the three species was suggested by their dispersion in the plane of the FCA. Calculation of a multiple linear regression (at the scale of 0.8 m2) showed negative relationships among these dominant species. Temporal homogeneity was indicated (at a scale of 0.8 m2) by dendrograms of species similarities among samples and by FCA performed on total biomasses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024478
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  • 5
    Electronic Resource
    Electronic Resource
    Physiological reactions to a change in light regime in cultured Skeletonema costatum (Bacillariophyta): implications for estimation of phytoplankton biomass (1996)
    Springer
    Hydrobiologia 333 (1996), S. 87-94 
    Details
    ISSN: 1573-5117
    Keywords: biomass determination ; light ; phytoplankton ; pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The marine planktonic diatom Skeletonema costatum (Cleve) was grown in batch culture under a 12 h light: 12 h dark (LD) regime for several generations before the experiment. At Time 0, half of the culture was transferred to continuous light (CL). Particulate organic carbon (POC), nitrogen (PON), and photosynthetic pigments (measured by spectrophotometry and high performance liquid chromatography) were monitored for 7 to 9 days in the two cultures. Under CL, POC and PON production were always lower. In addition, we measured a much higher proportion of chlorophyll degradation products (as chlorophyllid a, phaeophytin a and phaeophorbid a (PrD)). These indicate different physiological conditions between the two cultures, as reflected also be the lower POC/PON and chlorophyll a/POC ratios. Under CL illumination cells appear stressed, probably due to the total quantity of light to which cells are exposed. In fact, a higher proportion of the two xanthophylls diadinoxanthin and diatoxanthin in the CL culture indicates a photoprotective reaction of the cells. In contrast with the LD culture, parameters measured were not significantly inter-correlated in the CL culture. The lack of correlation between chlorophyll a and POC in CL does not encourage the use of the chlorophyll a/POC ratio as a biomass estimator. On the opposite, the ratio of total pigment content to POC did not vary much as a function of the light condition of the culture, remaining near 0.040 in both light regimes. Although further observations are needed, this index seems to be a reliable indicator of phytoplankton carbon biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017571
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  • 6
    Electronic Resource
    Electronic Resource
    Spatio-temporal variability in the gonad growth of Ophiothrix fragilis (Echinodermata: ophiuroidea) in the English Channel and estimation of carbon and nitrogen outputs towards the pelagic system (1999)
    Springer
    Hydrobiologia 414 (1999), S. 25-34 
    Details
    ISSN: 1573-5117
    Keywords: Echinodermata ; ophiuroidea ; reproduction ; gonad index ; carbon and nitrogen production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ophiothrix fragilis forms dense aggregations (up to 2000 individuals. m-2) and represents more than 60% of the biomass on the pebbles of the sessile epifauna community in the Dover Strait (eastern English Channel). This population shows a relative stability (in terms of density and magnitude of benthic recruitment) which contrasts with the variability of influx and of local hydrodynamical conditions. Gonadal change was studied in the Dover Strait during 1995 and 1996 and for another population offshore Roscoff (western English Channel) in 1996. Gonadal growth appeared to be cyclical, with higher gonad indices in June and July and a resting phase between September and February for the population of the English Channel. This change showed little inter-annual variability for the population of the Dover Strait, but a high spatial variability between populations of the English Channel. The population offshore Roscoff had lower gonad indices; this difference could be linked to lower temperature and lower food availability (phytoplanktonic production). However, whatever the gonadal growth pattern was, the main spawning of July was synchronous for females and males in both areas. Carbon and nitrogen production towards the pelagic system during the spawning period was very important (up to 20 g C. m-2 and 5 g N. m-2) and was up to 16% and 13% of the annual carbon and nitrogen production of the population in the Dover Strait. After the spawning period, larvae are brought under strong hydrodynamic conditions during ca. four weeks before metamorphosis and settlement. This is probably the most important period for the understanding of the stability of the population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003827532385
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  • 7
    Electronic Resource
    Electronic Resource
    Long-term changes (1979–1990) in three benthic communities (eastern English Channel): Use of factor analysis and rank-frequency diagrams for studying structural developments (1993)
    Springer
    Aquatic ecology 27 (1993), S. 415-426 
    Details
    ISSN: 1573-5125
    Keywords: benthos ; long-term series ; factor analysis ; rank-frequency diagrams ; trophic structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Long-term variations (1979–1990) of three benthic communities (Eastern Channel, France) were analysed by means of factor correspondence analysis (FCA), a multivariate method of ordination in reduced space, and rank-frequency diagrams (RFD). FCA distinguished periods of relative homogeneity and periods of strong variations in the structure of the communities. Two communities, the pebbles community and a rich and diverse mussel (Mytilus edulis) bed, showed great variations in the abundance of the main species (Ophiothrix fragilis in the first one, andM. edulis in the second one) which generated the enrichment of the community by their suspension-feeding behaviour. Beyond the multi-annual cycle induced by these variations, both communities seemed to be quite stable as no continuing trends could be seen. The third community, established on heterogeneous sand, also showed a multi-annual cycle linked to granulometric variations of the sediment. As passive supplies of detritus were not important and suspension feeders could hardly live in these conditions, the community stayed poor and was dominated by carnivores and deposit-feeders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02334803
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  • 8
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    Metabolic responses to temperature stress under elevated pCO2 in Crepidula fornicata (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-25
    Description: In the current context of environmental change, ocean acidification is predicted to affect the cellular processes, physiology and behaviour of all marine organisms, impacting survival, growth and reproduction. In relation to thermal tolerance limits, the effects of elevated p CO 2 could be expected to be more pronounced at the upper limits of the thermal tolerance window. Our study focused on Crepidula fornicata , an invasive gastropod which colonized shallow waters around European coasts during the 20th century. We investigated the effects of 10 weeks' exposure to current (380 µatm) and elevated (550, 750, 1,000 µatm) p CO 2 on this engineer species using an acute temperature increase (1 °C 12 h –1 ) as the test. Respiration rates were measured on both males (small individuals) and females (large individuals). Mortality increased suddenly from 34 °C, particularly in females. Respiration rate in C. fornicata increased linearly with temperature between 18 and 34 °C, but no differences were detected between the different p CO 2 conditions either in the regressions between respiration rate and temperature or in Q 10 values. In the same way, condition indices were similar in all the p CO 2 treatments at the end of the experiment, but decreased from the beginning of the experiment. This species was highly resistant to acute exposure to high temperature regardless of p CO 2 levels, even though food was limited during the experiment. Crepidula fornicata appears to have either developed resistance mechanisms or a strong phenotypic plasticity to deal with fluctuations of physicochemical parameters in its habitat. This suggests that invasive species may be more resistant to future environmental changes than its native competitors.
    Print ISSN: 0260-1230
    Electronic ISSN: 1464-3766
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    The stability of European rocky shore assemblages: variation across a latitudinal gradient and the role of canopy-forming macroalgae. (2012)
    Wiley-Blackwell
    In:  EPIC3Oikos, Wiley-Blackwell
    Details
    Publication Date: 2014-04-17
    Description: Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting the temporal stability of natural communities. Using the model of European intertidal rocky shore assemblages and collating 17 datasets, we investigated how the strength of these stability-enhancing mechanisms varies with latitude and how it can be altered by the loss of habitat-formers (e.g. canopy-forming macroalgae). Community stability decreased with increasing latitude, mostly as a consequence of a greater synchronization of species fluctuations. Statistical averaging and overyielding (i.e. richness effects) promoted stability, but their strength did not vary with latitude. The experimental removal of macroalgal canopies caused a strengthening of the statistical averaging effect that was consistent across the latitudinal gradient investigated. Nonetheless, the loss of canopies depressed stability by enhancing the synchronization of species fluctuations on southernmost shores, while it had weak effects on shores at higher latitudes. Variation in life-history traits among canopy-forming species and/or in prevailing environmental conditions across a gradient of latitude could underlie variable effects of habitat-formers on species fluctuations. Our study shows i) that the stability of intertidal assemblages and strength of compensatory dynamics varies with latitude, ii) that canopy-forming macroalgae, exerting a strong control on understorey species, can influence the strength of compensatory dynamics and iii) that biological forcing (i.e. facilitation) can be as important as environmental forcing in enhancing the synchronization of species fluctuations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
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    Status, trends and drivers of kelp forests in Europe: an expert assessment. (2016)
    Springer
    In:  EPIC3Biodivers Conserv, Springer, pp. 1-30
    Details
    Publication Date: 2016-06-16
    Description: A comprehensive expert consultation was conducted in order to assess the status, trends and the most important drivers of change in the abundance and geographical distribution of kelp forests in European waters. This consultation included an on-line questionnaire, results from a workshop and data provided by a selected group of experts working on kelp forest mapping and eco-evolutionary research. Differences in status and trends according to geographical areas, species identity and small-scale variations within the same habitat where shown by assembling and mapping kelp distribution and trend data. Significant data gaps for some geographical regions, like the Mediterranean and the southern Iberian Peninsula, were also identified. The data used for this study confirmed a general trend with decreasing abundance of some native kelp species at their southern distributional range limits and increasing abundance in other parts of their distribution (Saccharina latissima and Saccorhiza polyschides). The expansion of the introduced species Undaria pinnatifida was also registered. Drivers of observed changes in kelp forests distribution and abundance were assessed using experts’ opinions. Multiple possible drivers were identified, including global warming, sea urchin grazing, harvesting, pollution and fishing pressure, and their impact varied between geographical areas. Overall, the results highlight major threats for these ecosystems but also opportunities for conservation. Major requirements to ensure adequate protection of coastal kelp ecosystems along European coastlines are discussed, based on the local to regional gaps detected in the study.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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