Vulnerability of stream biota to climate change in mediterranean climate regions: a synthesis of ecological responses and conservation challenges

Abstract

Freshwater species worldwide are experiencing dramatic declines partly attributable to ongoing climate change. It is expected that the future effects of climate change could be particularly severe in mediterranean-climate regions (med-regions), which host many endemic species already under great stress from the high level of human development. In this article, we review the climate and climate-induced changes in streams of med-regions and the responses of stream biota, focusing on both observed and anticipated biological responses.We also discuss current knowledge gaps and conservation challenges. Expected climate alterations have already been observed in the last decades, and include: increased annual average air temperatures; decreased annual average precipitation; hydrologic alterations; and an increase in frequency, intensity, and duration of extreme events, such as floods, droughts, and fires. Recent observations, which are concordant with forecasts built, show stream biota of med-regions when facing climate changes tend to be displaced towards higher elevations and upper latitudes, communities tend to change their composition and homogenize, while some life-history traits seem to provide biota with resilience and resistance to adapt to the new conditions (as being short -lived, small, and resistant to low streamflow and desiccation). Nevertheless, such organism's responses may be insufficient to cope with current and future environmental changes. Accurate forecasts of biotic changes and possible adaptations are difficult to obtain in med-regions mainly because of the difficulty of distinguishing disturbances due to natural variability from the effects of climate change, particularly regarding hydrology. Long-term studies are needed to disentangle such variability and improve knowledge regarding the ecological responses and detection of earlywarning signals to climate change. Investments should focus on taxa beyond fish and macroinvertebrates, and in covering the less studied regions of Chile and South Africa. 3Scientists, policy makers, and water managers must be involved in the climate change dialogue because the freshwater conservation concerns are huge.

Mediterranean-climate streams and rivers: geographically separated but ecologically comparable freshwater systems

“…Species will face a trade-off between adaptation to new conditions or migration to new 856 habitats, although the particular life-history traits of species in med-rivers might allow 857 them to cope with climate changes up to a certain threshold (Filipe et al, 2013). In any 858 event, med-rivers will experience shifts in community richness and composition, 859 modifications of life-history traits, and, most likely will suffer local and regional 860 extinctions (Filipe et al, 2013).…”

“…In any 858 event, med-rivers will experience shifts in community richness and composition, 859 modifications of life-history traits, and, most likely will suffer local and regional 860 extinctions (Filipe et al, 2013). To avoid human disturbances, organisms in med-rivers may be able to find and 892 use refuges as they do with natural disturbances (Robson et al, 2013).…”

“…This is because salinization is a landscape-level disturbance whereashuman disturbances ultimately depends on the tolerance of species to a particular 899 disturbance (i.e., endurance strategies), their ability to find refuges during the 900 disturbance (i.e., avoidance strategies), and the presence of nearby non-disturbed 901 However, these models are still far from realistic because they usually overpredict 1007 species distributions. The incorporation of elements such as dispersal abilities, biotic 1008 interactions, long-term population or community variability, or complementary data on 1009 environmental requirements of species from laboratory experiments is necessary to 1010 provide more reliable results for management purposes (Filipe et al, 2013). The 1011 problem, in any case, is that climate change will favor species with higher temperature 1012 and pollution tolerance, and enable the establishment of new species introductions.…”

International Perspectives on the Effects of Climate Change on Inland Fisheries

“…A general reduction of annual discharge in the southern regions and an increase in the northern and higher altitude regions are anticipated. The duration, frequency, and intensity of floods and droughts will be exacerbated in the south (Figure 2), and runoff increases in winter and flow decreases in spring will be more frequent in northern and higher altitude areas (Arnell 1999;Christensen and Christensen 2003;Filipe et al 2013a).…”

“…Fishes are expected to be affected strongly by climate change, tending toward local extirpations or displacements to higher elevations and more northern latitudes (Filipe et al 2013a;Pletterbauer et al 2016). This implies a decrease in local species richness and major changes in the structure of assemblages for some regions, with the most favored species being those that are alien or common and having low conservation or commercial importance (Buisson et al 2008).…”