Mediterranean Temporary Ponds: values and threats

Fauna and flora of temporary ponds, including those of the Mediterranean areas (e.g., Gurney, 1909; Ghigi, 1921; Gauthier, 1928; Braun-Blanquet, 1936; Yaron, 1964) have been the subject of scientific interest since the beginning of the twentieth century (e.g., Murray, 1911; Mozley, 1932; Rzóska, 1961; Stout, 1964). However, the number of scientific publications on Mediterranean Temporary Ponds (MTPs) is not proportional to their ecological importance (Grillas et al., 2010) and only in recent years have they increased significantly (Boix et al., 2012) with the vegetation and fauna of Mediterranean wetlands being included in treatises of worldwide wetlands (e.g., Deil, 2005; Boix et al., 2016b). Also, the organization of specific scientific meetings (some of them listed in Box 1) and the release of research monographs or educational publications (examples in Box 2) from the end of the twentieth and beginning of the twenty first centuries reflects the growing interest in this habitat. All these efforts have highlighted the importance, abundance, functioning and biodiversity of MTPs and the need to develop conservation plans. MTPs have at least four characteristics that make the communities living in these environments interesting. Firstly, they are generally small, and ecological functioning of small waterbodies has been distinguished from those of large ones (Oertli et al., 2002; Søndergaard et al., 2005), e.g., their higher perimeter-to-area ratio enhances biogeochemical functions (Downing, 2010; Marton et al., 2015; Cohen et al., 2016). It is also noteworthy that small waterbodies on a global scale cover a total greater area than lakes (Downing et al., 2006), Secondly, as Mediterranean ecosystems, they are characterized by a combination of environmental features which imply a peculiar structure and dynamics of communities which show differences with respect to other temperate ecosystems (e.g., Coma et al., 2000; Peñuelas et al., 2007). Thirdly, they are included in the Mediterranean biome which covers a very small area, about 5% of the earth’s surface (Olson et al., 2001), but is identified as one of the worldwide biodiversity hotspots (Myers et al., 2000). Finally, they are associated with a highly distinctive (i.e., biodiversity value) flora and fauna (e.g., Giudicelli & Thiéry, 1998; Médail et al., 1998; Boix et al., 2001; Deil, 2005; Bagella & Caria, 2012), including some iconic or flagship taxa such as aquatic ferns, amphibians or large branchiopods and groups which achieved high species richness such as amphibious plant species, bryophytes, aquatic beetles or microcrustaceans (e.g., Ribera & Aguilera, 1996; Boix et al., 2008; Cogoni et al., 2009; Bagella & Caria, 2013).

Box 1 Workshops, symposia and conferences on (or including) MTPs
Full size table
Box 2 Special monographs or educational publications on MTPs
Full size table

From a global perspective, the conservation of the temporary aquatic environments is highly precarious, because their recognition has been historically neglected, and moreover, their degradation and disappearance have increased continuously during the last centuries (Brown, 1998; Rhazi et al., 2012). In MTPs, these issues are magnified due to the shallow water and the frequently small surface areas typical of these habitats (Boix et al., 2016b). Indeed, despite an improving public perception of wetlands over recent years, they are overlooked and exposed to perturbations or to total destruction (e.g., Grillas et al., 2004; Schwartz & Jenkins, 2000; Vendlinski, 2000) due to anthropogenic pressures, such as intensification of agriculture or land abandonment, overgrazing, hydrological perturbations, touristic/recreational uses, fires, introduction of exotic species and climate changes (Grillas et al., 2004; Zacharias et al., 2007). Over the years under these pressures, thousands of MTPs and entire pond landscapes have disappeared (Rhazi et al., 2012). Nevertheless, traditional land use is a key factor for MTP conservation. It is widely documented that plant diversity in these habitats has been maintained over the centuries by extensive human activities and land abandonment has negative effects on plant assemblages (Rhazi et al., 2001; Crosslé & Brock, 2002; Bagella et al., 2010b). Also, moderate disturbances by cattle are very important for plants (Bagella et al., 2010b) because they help to maintain diverse communities (Marty, 2005) and to control the colonization of shrubs and of opportunistic species from the surrounding areas (Rhazi et al., 2001; Ferchichi-Ben Jamaa et al., 2014). On the other hand overgrazing, particularly by cattle, causes water eutrophication, direct damage to the vegetation and physical disturbance (Bouahim et al., 2014). These perturbations also result in an impoverishment of the characteristic fauna of the habitat (e.g., Brown, 1998; Beja & Alcazar, 2003; Gascón et al., 2012).

The main threats connected with intensive agriculture are the drainage of lands, the pollution of water due to the use of pesticides and fertilizers and sediment deposition due to the ploughing in the catchment area (Lahr et al., 2000; Zacharias & Zamparas, 2010). Hydrological perturbations in MTPs are related not only to drainage for mosquitoes control, to gain new lands for urban development or agricultural activities, to collect water for irrigation, watering of livestock or domestic use (Aponte et al., 2010; Zacharias & Zamparas, 2010), but also to the extraction of raw materials which causes an increase in the duration of flooding (Grillas et al., 2004). MTPs are often stressed by inappropriate touristic/recreational uses such us horse riding, passage of cars and motorbike, establishment of car parking areas or even golf courses (Serrano & Serrano, 1996; Beja & Alcazar, 2003; Grillas et al., 2004; Serrano et al., 2006; Bouahim et al., 2010; Zacharias & Zamparas, 2010). The impact of fire is poorly studied. Certainly it favours perennial plant species with rhizomes or bulbs, whilst seed bank and animal populations could be positively or negatively affected (Grillas et al., 2004). The introduction of exotic plants contributes to the loss of habitat and sometimes seriously affects most low-altitude wetland areas (Grillas et al., 2004). Finally climate changes, resulting in modification of the seasonal and annual temperatures and in precipitation patterns and amounts, have a negative effect on MTPs. Indeed these climatic elements drive important hydrological processes which in turn control the ecology of MTPs (Dimitriou et al., 2009; Sim et al., 2013; Kneitel, 2014) and their modification, in the long term, puts the persistence plant and animal species at risk (Pyke, 2005).

PAULIS project: knowing biodiversity of Mediterranean Temporary Ponds

The opportunity for the organization of the International Symposium on MTPs was offered by the 3-year project “Vascular plants, bryophytes and aquatic fauna in Sardinian Mediterranean Temporary Ponds: biodiversity, ecology and conservation”, acronym PAULIS. The project, funded in 2012 by the local Administration of Sardinia (CRP-24943), was aimed at focusing interest on these neglected habitats through the implementation of scientific and educational products. The main objectives were: to quantify and characterize the taxonomical and functional diversity of vascular plants, bryophytes and aquatic fauna; to assess the main drivers of space–time variability of the habitat and the related biodiversity; to provide synthetic results to improve the effectiveness of conservation actions as well as to provide educational tools and products. The interdisciplinary team was formed from the Universities of Sassari (Italy), Cagliari (Italy) and Girona (Spain).

The prevalence of the toponym “paulis”, used in the Sardinian language to name MTPs, suggests that these habitats were formerly more abundant, with a strong perception at a local scale in the past. In spite of this, the lack of information on their ecology, biodiversity, temporal dynamics and spatial distribution on a regional scale has made their adequate consideration in conservation programmes more difficult. The opportunities provided by the Nature 2000 network was not adequately exploited because habitats 3110, 3120 and 3170*—to which MTPs could be referred—were rarely recognized inside the Sites of Community Importance and protected areas, or even left outside their boundaries. Moreover, the available scientific literature was scarce and difficult to access.

Almost 100 MTPs were monitored during the 3 years of the project (2012–2014). Three hundred and fifty species of vascular plants were found, of which 81 typical of MTPs (Bagella & Caria, 2012). Rare ferns, characteristic of the habitat were better represented than previously reported (Caria et al., 2013; Mascia et al., 2013; Bagella et al., 2015). Two hundred and twenty eight animal taxa were identified, of which 24% were referred to Diptera, 22% to Coleoptera, 14% to Branchiopoda and 8% to Ostracoda. Besides, some Turbellaria, Oligochaeta, Hirudinea, Gastropoda, Anostraca, Copepoda, Hydracarina, Ephemeroptera, Odonata, and Trichoptera were identified. Three species of amphibians were also found. Noteworthy records include the ostracod Paralimnocythere cf. messanai (first record from Sardinia); the corixid Cymatia rogenhoferi (third record for Italy), and the cladoceran Leydigia korovchinskyi (first record from Italy, J. Compte unpublished data). One hundred and thirty-nine bryophytes were also listed, of which two were new to Sardinia: Riccia huebeneriana Lindenb. and Hypnum revolutum (Mitt.) Lindb. var. revolutum.

Space–time variability of the habitat and the related biodiversity were evaluated at different spatial scales. The relevance of hydroperiod duration for the composition of vascular plant assemblages and species replacement throughout the season was emphasized (Bagella & Caria, 2013). The definition of the small-scale patterns of plant functional types and soil was one of the findings of the project: a positive correlation was found between Alfisols, aquatic and amphibious species, maximum water depth and hydroperiod and between Entisols, shallow water and terrestrial species (Caria et al., 2015). Differences in spatial and temporal patterns between plants and faunal groups in MTPs were only analyzed by a few studies in the past (see Rouissi et al., 2014; Ruhí et al., 2014). In contrast, this was one of the main goals of PAULIS project. Thus, variability of composition of plant assemblages was mainly related to space, whereas in the case of crustaceans, it was more related to time (Bagella et al., 2010b). Bryophyte distribution was instead controlled by hydroperiod and grazing livestock (Bagella, 2014; Marignani et al., 2015). Moreover, plants showed the lowest level of successional changes, coleopterans the highest and whilst in crustaceans this was intermediate (Bagella et al., 2011). Similarly, the effects of water, pond, and landscape variables on composition and taxa richness differed among phytoplankton, vascular plants, macroinvertebrates and amphibians, being environmental control group specific (Boix et al., 2016a). Datasets of Sardinian MTPs were also joined with those of a larger pond network in order to study general patterns in space and time. Basing on these data, Ballón et al. (2016) concluded that the environmental characteristics of MTPs are strongly influenced by their location, whereas their size has only a weak influence. Finally Ruhí et al. (2013) using a space-for-time substitution approach suggested that the invertebrate biodiversity embedded in MTPs could be affected by long-term climate changes.

MTPs are ideal habitats for engaging the public in practical actions, which could be strongly encouraged with the support of interactive identification guides. In the framework of the PAULIS project, an online interactive guide for the identification of plants growing in the MTPs http://dryades.units.it/stagnisardi_en/ was created. The guide, created with program FRIDA (FRiendly IDentificAtion), consists of two query interfaces: a multi-entry query permitting to specify several easily observable characters is followed by a richly illustrated dichotomous key to the species sharing those characters. Experts can also use the first interface to create keys to all species of a given taxon. The key is also available as a stand-alone application for Apple and Android mobile devices. The dissemination of the information and an increased awareness amongst the public, environmental managers and wardens is being promoted through the presentation of communications and posters in congress and seminars, the participation in public events, the engagement of students, the creation of a website http://paulisproject.jimdo.com/english/ and a Facebook community https://www.facebook.com/paulisproject?ref=hl, and the organization of the International Symposium on MTPs http://paulisproject.jimdo.com/english/international-symposium-sassari-april-15-16-17-2015/.

The International Symposium on Mediterranean Temporary Ponds

The International Symposium on MTPs, attended by 84 people from 14 countries, was aimed at offering an opportunity to researchers with different cultural backgrounds, students, practitioners, policy makers and other stakeholders for exchanging of experiences and information on the ecology, the biodiversity and the management of this type of habitat with the aim to promote effective practical conservation and to improve public awareness. The keynote presentations (4), oral (17) and poster contributions (44) were distributed among four sessions that covered the multi-faceted aspects of relevant knowledge about ponds in the fields of ecology and conservation issues, restoration and dissemination of the knowledge (Pisanu & Bagella, 2015). During the meeting, a public photo contest on MTPs involving 55 participants and 156 photos was also held http://paulisproject.jimdo.com/english/photo-contest/.

The results of an open questionnaire filled in the last day of the Symposium by the participants (Fig. 1) show the high level of cooperation between scientists, many of whom were young. At the same time, an urgency for effective conservation actions emerges, as well as the need to improve communication between science and society. The contents of communication and poster presentations, the papers published in the special issue, the key messages that emerged from the questionnaires and the results and deliverables of the PAULIS project suggest new challenges for the studies and the management of MTPs. Firstly, the scientific community focalized on the study of these habitats is very consistent, growing in the last years, distributed in several countries, and can rely on the contribution of the young generation. The cooperation for a multi-taxon approach also represents a strength and demonstrated a good attitude to interdisciplinarity of the scientists devoted to this habitat. The level of knowledge of taxonomic groups is unbalanced; nevertheless, specialists of neglected groups in the studies on MTPs, such as butterflies, flatworms, sponges and bryophytes, are now developing their researchers in this habitat (Pisanu & Bagella, 2015). All these aspects give high hopes for future cooperative research projects targeted to identify the key issues for their conservation, in order to provide tools for contrasting the high rate of disturbance which particularly affects non-European Mediterranean countries where the MTPs are not protected by legislation. Nevertheless, in matters of legislation, there is still much to do also in the European Union (Bagella, 2013). Indeed, the Habitats Directive (Council Directive 92/43/CEE) recognize only a small part of MTPs basing on the presence of target plant communities and excluding all the other ponds (Bagella et al., 2010a) which often host amphibians, macrocrustaceans and other organisms which need conservation measures. Moreover, the Water Framework Directive could represent a chance for the protection of MTPs in Europe, but unfortunately the local legislation of many states fixed 50 ha as the minimum size of a waterbody for its application. An answer to the destruction or degradation of ponds is offered by the creation of new ones, a relatively cheap and easy tool, as demonstrated by the Million Ponds Project http://freshwaterhabitats.org.uk/projects/million-ponds/. The difficulty to communicate with public and policy makers is another relevant barrier to the promotion of effective activities for conservation of MTPs, which requires a great effort for the dissemination of information and the increasing of awareness for the importance of this habitat. The sharing of some effective activities already launched is certainly a good starting point to reduce this gap.

Fig. 1
figure 1

Key messages for researchers and managers from the participants to the International Symposium on Mediterranean Temporary Ponds

Full size image

Special issue content

This special issue of Hydrobiologia contains a selection of 14 contributions presented during the conference. The precarious situation of conservation of temporary ponds in Mediterranean climate areas and the fact that temporary waters have been less studied than permanent, explain why this selection of papers contains manuscripts that focus on both management and research. Moreover, this selection also put in evidence the strong relationship between scientific researches and management in MTPs, since several of them include relevant information on both topics.

The effects of the existence of a dry phase make the temporary waters an excellent framework to study biotic adaptations of aquatic organisms, metacommunity dynamics and aquatic ecosystem functioning. In this sense, two papers, Manconi & Pronzato (2016) and Carta (2016), analyze the key adaptive strategies of sponges and the seed germination of plants in MTPs, respectively. At community level, four studies investigate the distribution and composition of assemblages, three of them taking crustaceans as the target group. Stoch et al. (2016) suggest that both dispersal limitation and species response to spatially structured environmental gradients might be involved in determining large branchiopod distribution in Tunisia. Alfonso et al. (2016) showed that in Apulia, crustaceans, in addition to macrophytes, can be used as an effective tool for identification of different pond types related to hydroperiod length. Similarly, Seminara et al. (2016) in Latium validated the use of crustaceans as an indicator of hydroperiod length, copepods being more effective in discriminating ponds with different wet phase duration. Cogoni et al. (2016) explain the influence of environmental variables on the distribution of a less-studied organism group in MTPs, bryophytes, and their tolerance to floods. Finally, at ecosystem level, Romo et al. (2016), Pinna et al. (2016) and Àvila et al. (2016) evaluated the differences in nutrient content between restored temporary and permanent dune ponds, the effect of summer droughts on leaf litter breakdown in temporary waters and the relative abundance of autotrophic and heterotrophic organisms in microbial food webs of temporary ponds located in the northeast of the Iberian Peninsula, respectively.

The effects of hydrology on community composition and adaptation and ecosystem functioning are included in several of the contributions referred to previously. However, two other papers of this selection focus on hydrology. Rodríguez-Rodríguez et al. (2016b) evaluated the temporal pattern of piezometric levels in a temporary playa lake in southern Spain, concluding that an urgent limitation of the ground water extraction from the carbonate aquifers is needed, and the usefulness of piezometric indicators in the management of MTPs. The use of hydrological models in the management of MTPs was also tested by Rodríguez-Rodríguez et al. (2016a), providing a result of a significant reduction of the hydroperiod under IPCC scenarios which, adding groundwater withdrawal within basin, predicts a high impact in the hydroperiod. Another example of human disturbance over MTPs located in Cape Town (Bird & Day, 2016) was also included in the selection. In this study, macroinvertebrates and microcrustaceans showed clear gradational changes in assemblage composition in relation to the surrounding cover of indigenous vegetation. Management proposals and tools were presented in two papers. Lumbreras et al. (2016) proposed a new tool to assess the conservation status of MTP based on 18 indicator species (including plants, large branchiopods and amphibians). A second proposal of a tool for monitoring long-term changes in plant community structure in Malta rock pools using phylogenetic patterns was done by Lanfranco et al. (2016). They proposed the calculus of some relatedness parameters for the early detection of long-term environmental changes.