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  • 1
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    Annual assessment of the predation of Mnemiopsis leidyi in a new invaded environment, the Kiel Fjord (Western Baltic Sea): a matter of concern? (2009)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 31 (7). pp. 729-738.
    Details
    Publication Date: 2019-09-23
    Description: The sudden occurrence of the ctenophore Mnemiopsis leidyi has been reported recently from different regions of the Baltic Sea and it has been suggested that the species has invaded the whole basin. Here we provide the first set of quantitative data of seasonal diet composition and life history traits of M. leidyi and its predatory role in the pelagic ecosystem of the Western Baltic Sea. The size structure of the species appeared to be dominated by small size classes and only a few adults were as large as those reported in the native region of the species and in other invaded areas. We show that the species has a high preference for small-sized and slow swimming prey, mainly during the winter low temperature period. Barnacle nauplii appeared to be the main source of carbon for the over-wintering population of M. leidyi. A preference for copepods was only found during August when these prey contributed up to 20% of the gut composition. In summer, planula larvae of the jellyfish Aurelia aurita were the most abundant prey in the gut content (feeding rate of 621 ind. ctenophore−1day−1). We further found that at highest densities of the species, in summer, a significant predation on its larvae occurs, this being the major carbon source of adults. Overall, these results are discussed in the context of trade-offs M. leidyi faces in the new environment and adverse environmental conditions, which are likely forcing the species toward reduced sizes and also probably reducing its potential predatory impact in the Baltic Sea.
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  • 2
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    Linking fisheries, trophic interactions and climate: threshold dynamics drive herring Clupea harengus growth in the central Baltic Sea (2010)
    Inter Research
    In:  Marine Ecology Progress Series, 413 . pp. 241-252.
    Details
    Publication Date: 2018-06-19
    Description: How multiple stressors influence fish stock dynamics is a crucial question in ecology in general and in fisheries science in particular. Using time-series covering a 30 yr period, we show that the body growth of the central Baltic Sea herring Clupea harengus, both in terms of condition and weight-at-age (WAA), has shifted from being mainly driven by hydro-climatic forces to an inter-specific density-dependent control. The shift in the mechanisms of regulation of herring growth is triggered by the abundance of sprat, the main food competitor for herring. Abundances of sprat above the threshold of ~18 × 1010 ind. decouple herring growth from hydro-climatic factors (i.e. salinity), and become the main driver of herring growth variations. At high sprat densities, herring growth is considerably lower than at low sprat levels, regardless of the salinity conditions, indicative of hysteresis in the response of herring growth to salinity changes. The threshold dynamic accurately explains the changes in herring growth during the past 3 decades and in turn contributes to elucidate the parallel drastic drop in herring spawning stock biomass. Studying the interplay between different stressors can provide fundamental information for the management of exploited resources. The management of the central Baltic herring stock should be adaptive and take into consideration the dual response of herring growth to hydro-climatic forces and food-web structure for a sound ecosystem approach to fisheries.
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  • 3
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    Pelagic population dynamics of Aureliasp. in French Mediterranean lagoons (2015)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 37 (5). pp. 1019-1035.
    Details
    Publication Date: 2017-05-02
    Description: The pelagic dynamics of the cosmopolitan scyphozoan Aurelia sp. was investigated in three French Mediterranean lagoons, Thau, Berre and Bages-Sigean, which harbour resident populations. The annual cycles showed a common univoltine pattern in all lagoons where the presence of pelagic stages in the water column lasted ∼8 months. Field observations showed a release of ephyrae in winter time followed by pronounced growth between April and July, when individuals reached the largest sizes, before disappearing from the water column. Maximum abundance of ephyrae and medusae were registered in Thau. Medusae abundance attained a maximum of 331 ind 100 m-3 in Thau, 18 ind 100 m-3 in Berre and 7 ind 100 m-3 in Bages-Sigean lagoons. Temperature and zooplankton abundance appeared as leading factors of growth, where Bages-Sigean showed the population with higher growth rates (2.66 mm day-1) and maximum size (32 cm), followed by Thau (0.57-2.56 mm day-1; 22.4 cm) and Berre (1.57-2.22 mm day-1; 17 cm). The quantification of environmental windows used by the species showed wider ranges than previously reported in the Mediterranean Sea, which suggests a wide ecological plasticity of Aurelia spp. populations in north-western Mediterranean lagoons.
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  • 4
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    Reconsidering evidence for Mnemiopsis invasion in European waters: reply (2010)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 32 (1). pp. 97-98.
    Details
    Publication Date: 2018-06-05
    Description: In their comment, Gorokhova and Lehtiniemi (Gorokhova and Lehtiniemi, 2010) raise doubts about the accuracy of the taxonomic identification of Mnemiopsis leidyi which has recently invaded the Baltic Sea. They question the conclusions of Javidpour et al. (Javidpour et al., 2009) that the observed feeding of adult M. leidyi on tentaculate ctenophore larvae indicates cannibalism, because the prey might also be larvae of other ctenophore species. We agree that morphotaxonomic distinction of M. leidyi-larvae from some other ctenophores species is difficult and molecular assays should be considered as a helpful tool besides taxonomic keys. The importance of molecular evidence has recently been emphasized for wider plankton studies by McManus and Katz (McManus and Katz, 2009). When we first observed the occurrence of M. leidyi in the Baltic Sea, we confirmed the morphological taxonomic identification by …
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  • 5
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    Synergistic effects of fishing-induced demographic changes and climate variation on fish population dynamics (2011)
    Inter Research
    In:  Marine Ecology Progress Series, 426 . pp. 1-12.
    Details
    Publication Date: 2018-06-22
    Description: The synergistic effects of fishing, climate and internal dynamics on population fluctuations are poorly understood due to the complexity of these interactions. In this paper, we combine time series analysis and simulations to investigate the long-term dynamics of an overexploited population in the Mediterranean Sea, and its link with both fishing-induced demographic changes and hydroclimatic variability. We show that the cyclicity of the catch per unit of effort (CPUE) of European hake Merluccius merluccius (EH) vanished in the 1980s, while the correlation between the CPUE and a local environmental index increased. Using simulations, we then show that the cyclicity observed in the EH biomass before the 1980s can have an internal origin, while that its disappearance could be due to the fishing-induced erosion of the age structure. Our results suggest that fishing can trigger a switch from internally generated to externally forced population fluctuations, the latter being characterised by an increasing dependency of the population on recruitment and ultimately on environmental variability. Hydroclimatic modifications occurring in the Mediterranean in the early 1980s could have enhanced these changes by leading to a mismatch between early life stages of EH and favorable environmental conditions. Our conclusions underline the key effect of the interaction between exploitation and climate on the dynamics of EH and its important consequences for management and conservation.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 6
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    Decadal changes in water temperature and ecological time-series in Lake Geneva, Europe - detecting relationships with the subtropical Atlantic climate variability (2007)
    Inter Research
    In:  Climate Research, 34 (1). pp. 15-23.
    Details
    Publication Date: 2019-01-21
    Description: We investigated connections between subtropical Atlantic climate variability, atmospheric conditions in the European Alpine region (45 to 47° N and 5 to 8° E) and the interannual variability of the thermal conditions in the largest body of freshwater in Western Europe (Lake Geneva). The long-term water temperature was related to climate variability by means of a multivariate regression model. Results revealed atmospheric connections that have been elusive so far, and showed that over the period from 1959 to 2000, summer thermal conditions in Lake Geneva appear tightly linked to the long-term variability of the subtropical Atlantic climate. The multivariate model revealed high skills and tight correlations, which suggest the possibility of assessing future thermal changes in Lake Geneva from the Atlantic climate variability. The implications of such climatic forcing on the functioning of the pelagic ecosystem in Lake Geneva were illustrated by analysing the long-term changes in abundance of the summer-dominant carnivorous cladocerans Bythotrephes longimanus and Leptodora kindtii during the period 1974 to 2000. Again, the multivariate model revealed high skills and excellent correlations between the interannual changes in abundance of these species and the variability of summer climate. Our approach provides a general understanding of the interrelations between large- and regional-scale climates, local environmental conditions and the ecological responses in Lake Geneva during summer, and is therefore applicable to other retrospective studies.
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  • 7
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    Dominance of the planktonic diatom Thalassiosira minima in recent summers in the Bahia Blanca Estuary, Argentina (2012)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 34 (11). pp. 995-1000.
    Details
    Publication Date: 2018-06-06
    Description: The diatom Thalassiosira minima was first recorded in the Baha Blanca Estuary in 1992. In 19921993 it exhibited a broad seasonal occurrence. A recent survey (20062007) showed a seasonal appearance restricted mainly to summer together with a greater relative abundance within the phytoplankton. A close connection was found with warmer, more saline and highly turbid conditions experienced in recent summers in the estuary. Whether these changes will impact the estuary trophic dynamics remains an open question.
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  • 8
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    Seasonal and interannual variability of cladoceran communities in two peri-alpine lakes: uncoupled response to the 2003 heat wave (2010)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 32 . pp. 913-925.
    Details
    Publication Date: 2018-06-05
    Description: Seasonal and interannual dynamics of cladoceran species were analyzed during the period 1995–2003 in two deep peri-alpine lakes morphologically different but subjected to similar regional climatic forcing. The seasonal succession of cladoceran species was characterized and the impact of extreme climatic events on the annual pattern of species succession was assessed. Using a multivariate method, we show that the cladoceran species display marked seasonality patterns that differed in the two lakes. The differences observed between the lakes were driven by their trophic state, the plankton species composition and the abundance of predators. We show that the sensitivity of the annual pattern of species succession to extreme weather changes, illustrated by the 2003 heat wave, differs markedly in these two lakes. In Lake Annecy, the annual pattern of cladoceran succession observed in 2003 is not different from the one usually observed. In contrast, in Lake Geneva, the annual pattern recorded in 2003 is unusual and characterized by the maintenance of herbivorous cladocera during summer. These findings underline the need to consider the morphology of lakes and trophic state in the assessment of ecological responses to global warming. Our results contribute to the debate about the predictability of the impacts of climate change on aquatic ecosystems, and their extrapolation from one site to another.
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  • 9
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    Quantifying top-down control and ecological traits of the scyphozoan Aurelia aurita through a dynamic plankton model (2018)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 40 (6). pp. 678-692.
    Details
    Publication Date: 2021-02-08
    Description: Aurelia aurita (Linneaus, 1758) is a cosmopolitan scyphozoan, probably the most investigated jellyfish in temperate and highly productive coastal ecosystems. Despite a prominent top-down control in plankton food webs, a mechanistic understanding of A. aurita population dynamics and trophic interactions has been barely addressed. Here we develop a food web dynamic model to assess A. aurita role in the seasonal plankton dynamics of the Kiel Fjord, southwestern Baltic Sea. The model couples low trophic level dynamics, based on a classical Nutrient Phytoplankton Zooplankton Detritus (NPZD) model, to a stage-resolved copepod model (referencing Pseudocalanus sp.) and a jellyfish model (A. aurita ephyra and medusa) as consumers and predators, respectively. Simulations showed the relevance of high abundances of A. aurita, which appear related with warm winter temperatures, promoting a shift from a copepod-dominated food web to a ciliate and medusa dominated one. The model captured the intraspecific competition triggered by the medusae abundance and characterized by a negative relationship between population density and individual size/weight. Our results provide a mechanistic understanding of an emergent trait such as size shaping the food web functioning, driving predation rates and population dynamics of A. aurita, driving its sexual reproductive strategy at the end of the pelagic phase.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 10
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    Trade-offs of the copepod Eurytemora affinis in mega-tidal estuaries: insights from high frequency sampling in the Seine estuary (2008)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 30 (12). pp. 1329-1342.
    Details
    Publication Date: 2018-06-05
    Description: Zooplankton trade-offs to maximize fitness in highly dynamic environments such as estuaries have long been a question of central importance for understanding the ecology and evolution of estuarine populations. We present here the first comprehensive data set on the population dynamics of the copepod Eurytemmora affinis obtained from 50 h high-frequency sampling in the Seine estuary during spring. Maximum densities of E. affinis were associated with low salinities (0.5–10) and recorded during the ebb in the bottom layer. Vertical variations in population structure were observed between ebb and flood, as well as the spatial distribution of developmental stages. Nauplii were concentrated in the low salinity zone just above salinity 5, and copepodids and adults distributed more widely relative to salinity than nauplii in bottom waters, whereas the opposite pattern was observed in surface waters. The sex-ratio and the proportion “ovigerous females:non-ovigerous females” appeared to be related to tidal cycle and depth, with higher relative densities of non-ovigerous females in bottom waters and around low tide. The vertical variations noticed during the tidal cycle suggest a strategy by the species to avoid flushing by surface currents, although it may incur a cost due to the greater presence of predators in bottom waters.
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