Repercussions of the Abandonment of Mediterranean Saltpans on Waterbird Communities
WATERBIRDS, 25 (4): 492-498 (2002)
MARIANO PARACUELLOS 1,4, HERMELINDO CASTRO 2, JUAN CARLOS NEVADO 1, JOSÉ ANTONIO OÑA 3, JOSÉ JAVIER MATAMALA 1, LORENZO GARCÍA 3 AND GABRIEL SALAS 3
1 Department of Flora and Fauna, Consejería de Medio Ambiente, Junta de Andalucía, C. R. Oliveros, bl. Singular, 04071, Almería, Spain
2 Department of Vegetal Biology and Ecology, Almería University, Cañada de San Urbano, s/n, 04120, Almería, Spain
3 Department of Ecology of Arid Zones, Estación Experimental de Zonas Áridas, Consejo Superior de Investigaciones Científicas, C/ General Segura, 1, 04001, Almería, Spain
4 Internet: email@example.com
Abstract.- The richness and abundance of waterbird species were compared in active and abandoned saltpans in southeastern Spain. The effects of traditional methods of salt extraction in Mediterranean wetlands on the avian community were evaluated, as well as the effects of the abandonment of coastal salinas in Europe due to their present low profitability. Major changes in the waterbird community were found in disused saltpans, which were mainly due to environmental changes after salt production ceased. The diversity of bird species and the abundance of the diving species increased following abandonment, but the number of Greater Flamingo (Phoenicopterus ruber) and some shorebirds declined. Management measures required to improve the ornithological diversity in abandoned saltpans are proposed.
Key-words.- Community, conservation, ecological effects, morphology, salinas, saltpans, waterbirds.
Human exploitation during the 20th century has had major impacts on the ecological communities in wetlands (Finlayson et al. 1992; Yuma 1993; Montes et al. 1995; Barbosa 1997; Murias et al. 1997; Marques and Vicente 1999). One use of wetlands in Europe has been the precipitation and collection of marine salt in marshes or coastal salinae (Casado and Montes 1995; Bradley 1997). This utilisation, normally associated with modifications of the original characteristics of the aquatic systems, has usually favored those bird species dependent on saline or hypersaline habitats (Hidalgo 1991; Robledano et al. 1992; Castro 1993; Pérez-Hurtado and Hortas 1993; Barbosa 1997; Murias et al. 1997). Various authors agree that the abandonment of this industrial activity or its transformation to other uses have negative repercussions on the avifauna (Finlayson et al. 1992; Pérez-Hurtado et al. 1993; López Carrique et al. 1996; Bradley 1997; Viada 1999). However, during recent decades, the saltpan industry on European coasts has entered a phase of decline due to economic recession, with consequential changes in the use of the wetlands (Anonymous 1992; Castro 1993; Casado and Montes 1995; Montes et al. 1995). Thus in many regions, such as southeastern Spain, the majority of salinas have been permanently closed (Robledano et al. 1992; Matamala 1996). There is a need to evaluate the effects of this widespread abandonment of saltpans on their avian communities.
In the present study, we analyse the effects of the cessation of salt production in salinas in southeastern Spain on their waterbird community. We compare the avifauna before and after abandonment and contrast it with those found on other saltpans that remain active. Management strategies to improve the diversity and numbers of birds in the abandoned salinas are proposed.
STUDY AREA AND METHODS
We studied two saltpan complexes, Salinas de Cabo de Gata and Salinas de Cerrillos (CG and CE respectively). The former was still in use and the latter was abandoned in 1988. Both areas are now protected and considered of international importance to birds (Guirado et al. 1997; Viada 1999).
The two complexes are located in the Bay of Almería and separated by 40 km (Almería, southeast Spain; CG: 36º47’N, 2º14’W; CE: 36º44’N, 2º40’W). This region has low and seasonal rainfall, with the highest levels between September and February and lowest in July and August (Capel 1990).
These saltpan complexes were established in extensive natural coastal lowlands (Castro 1993; Sánchez and Molina 1996). Until 1988, both sites were in full working order, introducing seawater to a series of different types of pools (evaporators, heaters and crystallisers). Evaporation loss, decanting of iron oxides, carbonates and gypsum occurred, until water reached the precipitation pans or crystallisers, where the salt was harvested (principally sodium chloride; Vieira 1989; Castro 1993). This traditional method, still in use at CG, was responsible for the characteristics of the shallow and euhaline-hypersaline wetlands with high and permanent levels of flooding. At the end of the 1980s, the direct entry of seawater was stopped at CE when salt production ceased. As a consequence, lagoons in this wetland returned to something approaching their original state.
While the ecological characteristics of CG remain the same, those of CE have been altered as follows (Table 1): i) the area of shallow and saline water was reduced by about 50%, becoming seasonal and dependent on rainfall; ii) given the lack of the control of water-level, underground water from local aquifers (supersaturated and contaminated by nutrients over the years) increased the water depth in some of the pools; iii) the salinity was lowered in such zones; iv) the cessation of seawater inflow, and the input of subterranean water increased the primary productivity of these flooded areas; v) the loss of salinity favored the increase of helophyte cover on the banks of such pools (for further information, see Sánchez and Molina 1996; Ortega et al. 2000).
With the aim of evaluating the possible variations in the waterbird community at CE in relation to the change of use after 1988, CG and CE were monitored simultaneously from 1979 onwards with the former acting as a control where no transformations had occurred.
Table 1. The main environmental characteristics of Salinas de Cabo de Gata and Salinas de Cerrillos after 1988 (citing values from 1997). Surface area: total size of the wetland; Flooding level: average proportion of the area flooded in the winter (November-February) and summer (July-September) with respect to the total surface; Depth: the maximum water depth; Salinity: the average salinity over 12 months; pH: average pH value; PO4-3: average concentration of the phosphates; NO3-: average concentration of the nitrates; Chlorophyll-a, the average concentration of Chlorophyll-a; Helophyte coverage, the proportion of the total perimeter of the shore occupied by helophytes. Some data from Ortega et al. (2000).
The study was carried out during the two periods of the year, winter (November to February) and summer (July to October), when the birds made a more intense use of the wetlands (Paracuellos 2001).
The counts of waterbirds made at CE before and after its abandonment were compared, as well as at CG for the same periods (1979-1988 and 1990-2000 respectively). The average value of the species richness and abundance of the bird species was calculated for the winter and summer seasons, for the periods before and after 1988.
For a community-scale study, only the waterbird species which used the salinas principally for feeding were taken into account. The species selected were divided into four guilds, according to their food searching behavior (Perrins and Ogilvie 1998): i) wading birds: Ardeidae, Threskiornithidae, Ciconiidae, Phoenicopteridae and Gruidae; ii) shorebirds: Rallidae except Common Coot (Fulica atra), Haematopodidae, Recurvirostridae, Charadriidae and Scolopacidae; iii) dabblers: Anserini, Tadornini and Anatini; iv) divers: Podicipedidae, Aythyni, Oxyurini and Common Coot. Moreover, to carry out the analysis for each site and for each period (before or after 1988), only those species with an average of at least 20 individuals in one or both areas were considered (Tables 2 and 3).
The relationship between the percentage change in numbers of the principal species of shorebirds before and after 1988 (Tables 2 and 3; ((ai – bi) x bi-1) x 100; where bi and ai were the average values of the abundance of the species i in the periods before and after 1988 respectively) and the average lengths of their respective tarsi and bills (sizes according to Perrins and Ogilvie 1998) were also considered.
Differences in average values were tested for statistical significance using the Mann-Whitney U test, and the G test for frequencies. The analysis of relationships between pairs of variables were made using the Spearman rank correlation (Siegel and Castellan 1988).
During the study period, 53 and 66 waterbird species used the salinas for feeding at CG and CE respectively. When comparing the average values of the number of observed species, there were no important changes in the species richness at CG before and after 1988, but at CE there was a significant increase in richness (Fig. 1). This increase was mainly due to the addition of diving species not previously observed in the area (six new diving species against three wading birds, one shorebird and two dabblers).
The wading birds and the shorebirds were always the most abundant species in the CG community (Fig. 2). Although at CE the latter group were also dominant before its disuse, from 1988 the diving bird guild contributed a greater proportion to the total number of individual birds, and shorebirds shortly decreased in number (Fig. 2).
Table 2. Average abundance (± SD) during winter of the main waterbird species at Salinas de Cabo de Gata and Salinas de Cerrillos before and after 1988. Statistical differences (Mann-Whitney U test) between both intervals are indicated: n.s., not significant; *, P < 0.05; **, P < 0.01. N, sample size (number of years). Guilds: o, wading birds; ●, shorebirds; +, dabblers; □, divers.