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Linking climate and anthropogenic stress to life histories of three pelagic populations of the Mediterranean Sea

2010Plankton variability in the Mediterranean sea. Insights from crustacean and gelatinous zooplanktonLOPEZ LOPEZ Lucia (Spain)
Organisation:Christian Albrechts University, Kiel (DE)Supervisor :Dr. Sommer & Dr. Mounero
Summary: Global Changes (i.e. climate change, eutrophication, overfishing, habitat alteration) have a wide range of effects on European marine ecosystems, and have also widespread economic implications. The assessment, forecast and possible mitigation of such consequences require a prior understanding of how the adaptive abilities of marine populations response to the rate of change of stress factors, and ultimately on the limits of population persistence. In recent years, growing evidence has shown marked changes in the Mediterranean Sea including mass mortality events of benthic fauna, long term changes in deep sea food webs, conspicuous modifications in species distribution, phenology of plankton, and a regime change in the middle 1980s. Such changes may be exacerbated in scenarios of global change, which may have substantial implications for conservation biology and resources management in the Mediterranean Sea. Although plankton populations are recognized as sentinels of marine ecosystem change because they are crucial mediators in the biophysical coupling: environment – primary production - fish production, attempts to link the life history of plankton species with Global Change have been scarce. In this work we aim at integrating biological time-series of three pelagic populations to address the adaptive ability of key species belonging to main functional groups in the pelagic food web: Centropages typicus (pelagic copepod), Pelagia noctiluca (gelatinous carnivore), and Engraulis encrasicolus (small pelagic fish). In fact, copepods support most of the marine food web, jellyfish are key drivers of the top-down control on plankton, as well as eggs and fish larvae, whereas anchovy is highly sensitive to bottom up forces (plankton changes) and further undergoes a heavy fishing pressure in the Mediterranean Sea. Here, we have mined a large dataset covering three decades of species abundance, that has been analysed in a meta-analysis framework. Examination of biological time series and demography of species in regards to climate variability allows to identify and quantify the strength of the link, while the comparison between different locations and combination of the results in a statistically robust way will allow to draw a theoretical framework for climate plankton interaction. The preliminary results of the research carried out on C. typicus in the Ligurian Sea are presented here. We first characterized the long term variations in hydroclimatic conditions in the Mediterranean Sea throughout the period 1948-2009. We identified a hydroclimatic shift in the beginning of the 80s and assessed its possible consequences for the C. typicus. Attending to the functional responses of this copepod, we found that a temperature window between 15-16.5 °C maximise the fitness of the species, whereas temperatures under 10°C and over 20°C substantially reduce its fecundity and growth rate. Our analysis identify a jellyfish abundance threshold (0.49 ind/m3) under which the population of C. typicus is not significantly affected by predation, suggesting that the predator-prey link evolves in a nonstationary way. The analysis of population stability based on spectral decomposition indicates a close dependence of this with population abundance. At lower abundances the population of C. typicus might not be able to buffer climate forcing, increasing the sensitivity to climatic intermittences and the risk of entering a dynamic with a higher extinction risk. Our study highlights the need of an integrated approach to investigate population dynamics, combining concepts of niche ecology and population theory, which allows determining critical ranges of environmental change for this species. Ultimately, our results stress the need of experimental studies in order to determine genetic variability and species plasticity.