Trends in Ecology & Evolution
ReviewClimate change effects on a miniature ocean: the highly diverse, highly impacted Mediterranean Sea
Section snippets
The Mediterranean: a miniature model of the world's oceans
The Mediterranean is a peculiar sea, a product of a tormented geological history, where continents collide and water masses come and go, a crossroads of biogeographical influences between cold temperate biota and subtropical species (see Box 1). During the Mesozoic, it also united the Atlantic and Pacific realms through a large ocean known as the Tethys. The legacy of the Tethys and later geological events have produced a marine life that is unusually diverse for such a small enclosed sea; it
Physical evidence of changes in the Mediterranean
The Mediterranean Sea displays a specific hydrology, with well-identified water masses in each sub-basin (Figure 1) and at different depths. One peculiarity is a homogeneous deep-water layer below ∼250 m that does not get colder than 12–13 °C. The general thermohaline circulation of the Mediterranean is determined by the flux of incoming Atlantic water by the Gibraltar Straits and by the sinking of waters formed at the three coldest areas of the sea: the Gulf of Lions, the northern Adriatic and
Towards homogenisation of the Mediterranean biota?
The Mediterranean marine biota has historically been divided into three biogeographical provinces (the western and eastern basins, and the Adriatic Sea; Figure 1), each subdivided along latitudinal patterns [30]. Species of sub-tropical origin are therefore more abundant in southern parts of these provinces whereas temperate species dominate the northern parts (Box 1). Climate change, through long-term temperature increase and a higher frequency of short-term extreme events, is undoubtedly
Recurrence of diseases leads to increased stress levels
Heat stress is recognised to trigger diseases at sea, with the frequency of these events clearly increasing over the last two decades 53, 54. Recent extreme temperature events are likely to have disturbed the normal functioning of biological systems. Species present a ‘natural’ range of thermal tolerance and respond to natural temperature fluctuations by physiological, biochemical and molecular adaptations. Acute physiological stress, leading to diseases and mass mortality, appears when
Effects of climate change on ecosystem functioning
Adaptive responses to large-scale perturbations such as climate change affect all biological levels. They initially take place at the individual levels but are integrated and translated to upper levels [75]. Environmental parameters, individual organism responses and species interactions, constitute the framework of the ecosystem's dynamic equilibrium. Any change in these parameters must have functional consequences, especially when they involve structuring, key and/or engineer species.
Conclusions
The spectacular alterations described above will drive the Mediterranean into uncharted territory, and human interactions with marine life will probably be severely affected. The effects that climate change will have on this region should serve as an example of what could happen globally. We must take the opportunity of an increasing awareness on all sides of this miniature ocean to establish a solid network of observatories that will serve a global purpose, beyond the Mediterranean. Regional
Acknowledgements
This paper is dedicated to the memory of L. Laubier, colleague, mentor, a great naturalist and an inspirational human being. We are deeply indebted to the many colleagues and co-authors of previous works who in some way have participated to the genesis of this review, and particularly to: D. Bellan-Santini, N. Boury-Esnault, B. De Ligondes, J. Garrabou, R. Graille, J.G. Harmelin, M. Harmelin-Vivien, J.C. Romano, S. Ruitton, J. Vacelet, M. Verlaque and H. Zibrowius. Special thanks to I. Olivieri.
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