Advances in Mountain and Mediterranean Wetlands Conservation

It is well known that wetlands are one of the most threatened ecosystems in the world, being also considered as environments with great natural, economic, and socio-cultural values. The impacts on these ecosystems are clearly evident in the Mediterranean region, where water is a limited resource. In this sense, since ancient times, Mediterranean wetlands have been exposed to the pressure of human activities. The existence of a wide variety of resources, such as water supply for agriculture or livestock, fishing or hunting, among others, did not go unnoticed by ancient civilizations [1]. These impacts continued throughout history, reaching the present day. However, it is from the Industrial Revolution, as a result of the mechanization and the demographic growth, when these impacts became more evident.

The importance of these ecosystems from a global perspective is highlighted in this Special Issue, in the manuscript of de Vicente [2]. This author highlights the high provision of wetland ecosystem services, indicating that wetlands are considered as the “hotspot” for biogeochemical transformation worldwide. In a scenario of global change, the hydrological regime and therefore the biogeochemical processes will be altered, an aspect that is evident in Mediterranean wetlands. In this context, this study shows the role of sediments in the biogeochemistry of wetlands, analyzing the effect of hydrological changes in phosphorus dynamics—one of the major nutrients limiting production in freshwater ecosystems—and greenhouse gas emissions.

In this context of global and climate change, Mediterranean wetlands will be even more exposed to uneven hydroperiods with high intra- and interannual oscillations in their environmental conditions—it is important to note that many of them are temporary wetlands—. These fluctuations in limnological features will also be responsible for changes in the structure and dynamics of the biotic communities. The manuscript of Gilbert et al. [3] explores precisely this aspect in a set of Mediterranean wetlands, indicating which drivers are controlling the seasonal replacement of zooplankton species; in this case specifically being mainly the concentration of chlorophyll-a, water transparency, total nitrogen concentration, and some morphological variables such as depth and surface area. These authors, like many zooplanktologists, remark the necessity to monitor the zooplankton community to evaluate the effect of anthropogenic activities on aquatic ecosystems in the future. In the same sense, Reul and collaborators [4] present a case study in an extreme Mediterranean wetland (sulfide-rich thermal spring), evaluating the triggers controlling the annual cycle of cyanobacterium Oscillatoria sp. These authors highlight that, contrary to the classic accepted model of ecological succession in the phytoplankton community of epicontinental waters, neither nutrients nor light, but one selective agent (sulfide) positively triggers the proliferation of Oscillatoria sp. in the summer season.

The role of plankton communities as bioindicators is evaluated in two papers included in this Special Issue. Borrego-Ramos et al. [5] used benthic diatoms, a well-known bioindicator community proposed by European legislation, and compared their use under two different approaches: (i) the traditional microscopy and morphological identifications, and (ii) metabarcoding approaches. The validation of DNA-based methods, with similar results in 59% of the studied ponds, represent an important goal for the monitorization of Mediterranean ponds. On the other hand, Souissi and Souissi [6] promote in their manuscript the use of sentinel specimens in the water column, specifically through the use of body size and the fertility of the egg-bearing calanoid copepods. This new ecological indicator (quality index QI)—that could be generalized to different aquatic ecosystems and reflect perfectly the stress provoked by sudden changes in hydro-climatic conditions—represents a development of this sentinel species methodology that has been more widely applied in benthic organisms and cladocerans.

However, it is important to note that the anthropogenic impacts have not been the same throughout the territory, with greater consequences in wetlands located in coastal areas, valleys or countryside—in which agriculture and urban growth have drastically transformed the structure and functioning of these unique ecosystems—and minor ones in the middle and high mountain areas. Aquatic ecosystems located in mountain areas were traditionally well preserved, but today also suffer the impact of human activities. All of these impacts are diverse, ranging from those derived from global or climate change to others of a diverse nature generated at a local scale that cause serious environmental problems such as the loss of biodiversity and wetlands, the alteration of hydroperiod, or the deterioration of water quality.

The problem with these mountain wetlands is increased by (i) their small size that leaves many of them out of inclusion in wetland inventories; (ii) the limited knowledge that the scientific community has of them—many of them are even unknown to most of civil society—; and (iii) the scarce information that exists on its limnological features and biotic communities due to the previously mentioned lack of knowledge and by the hard access that makes its study difficult. This aspect is clearly demonstrated in the recent literature where new species have been discovered for science in Mediterranean mountain ponds [7,8,9], as well as in the manuscript by Marrone et al. [10] where the presence of the calanoid copepod Metadiaptomus chevreuxi is mentioned for the first time in the Iberian Peninsula. The presence of a rich endemic biota in these ecosystems highlights the necessity to increase the knowledge of these ponds to discover this hidden diversity that would assign value many of these ecosystems.

In addition, one of the biggest problems that must be addressed in these ponds is related to the arrival or introduction of exotic species. These species can arrive naturally, as has recently been shown [11], in alpine ponds of the Sierra Nevada National Park (southern Spain), or by human introduction for commercial or recreational fishing purposes. This is the theme of the last manuscript of this Special Issue, in which Pastorino and collaborators [12] show the pressure exerted by the brook trout on the zooplankton and aquatic insect community in mountain wetlands of the Cottian Alps, highlighting the need for the extinction of these invasive fish populations.

Finally, it is necessary to show that under a global change scenario, the negative impact on wetlands will continue. Given this situation, it is clear that it is necessary to study and adopt measures to guarantee the conservation of these unique ecosystems [13]. Understanding these ecological problems is a key concern for conservation biology, as it is essential to do research into these threats in order to develop adequate management plans.