Detecting drought induced environmental changes in a Mediterranean wetland by remote sensing.

1.
The coastal area of Valencia (Spain) in the Western Mediterranean is rich in freshwater and brackish wetlands. These areas are mostly protected for bird conservation but are also highly affected by human impacts. Six shallow lakes located in Ramsar wetland sites of this area were studied in order to assess past and present ostracod biodiversity and relate it to the status of the lakes, taking into consideration the indicator value of these easily fossilizable crustaceans.

2.
In all the wetlands studied, ostracod taphocoenoses showed much higher species richness than the corresponding biocoenoses. This is expected from the time accumulative character of the taphocoenosis, but the trend is clearly evident in the most disturbed sites which indicated loss of ostracod diversity owing to human impacts.

3.
By considering the ecology of most frequent species, multivariate ordination of both tapho- and biocoenoses showed trends within and between lakes in their limnological status, which were related mainly to water chemistry, and also to temporality and eutrophication to a certain extent. Some lakes have apparently lost most of their past ostracod community owing to an increasing trophic status in some cases and to modifications of the hydrological regime in others.



Copyright © 2007 John Wiley & Sons, Ltd.

Loss of Ostracoda biodiversity in Western Mediterranean wetlands

The hatching of diapausing eggs from sediment samples of ponds and lakes is a fast, easy, and economical technique proven useful for the assessment of diversity and abundance of zooplankton in permanent habitats. Here, we extend and optimize this approach for temporary brackish ponds which may experience great within-year variation in salinity conditions. We studied the species and numbers of rotifers emerging from the sediments of several brackish ponds and saline lakes from Eastern Spain incubated at the full range of salinity conditions observed at the study sites. On average, 82 % of the total observed species in weekly sampling for one year were detected in a single sample of both the sediments and water column. No statistical difference was found between both methods. However, some rotifer species were only observed in the water column samples, but not in sediment hatchlings, and vice versa. We concluded that both methods are not exhaustive by themselves but are complementary. Salinity affected the estimation of both rotifer richness and the density of individuals of each rotifer species that emerged from the incubated sediments. Differences in the density of emerging animals were also found among sites and among combinations of sites and salinities. The latter result indicates that in order to obtain an estimate of the emergence rate for each rotifer species present at a site, it is necessary to incubate sediments at salinity conditions close to their local values.

Assessing rotifer diapausing egg bank diversity and abundance in brackish temporary environments : an ex situ sediment incubation approach

We studied the Cladocera in four shallow brackish lakes at El Hondo and Salinas de Santa Pola in Mediterranean Spain from February 1999 to June 2000, sampling each month. We recorded five species : Daphnia magna, D. pulex, D. longispina, Simocephalus exspinosus and Moina brachiata. D. magna was the most abundant species and the only one present all year round. Total abundance of Cladocera varied significantly between wetlands and months, and was highest in the largest, deepest, least saline wetlands. For a given wetland and month, abundance increased at points of greater depth or lower salinity. Species richness of Cladocera was highest in those seasons and lakes where salinity was lowest, and in those seasons and lakes where cladoceran abundance was highest. These wetlands hold a particularly high number of waterbird species, but a very low number of Cladocera species. Ready dispersal via waterbirds does not appear to promote cladoceran diversity in this system, owing to local conditions such as high salinity. We suggest that the conservation value of wetlands for birds is not a good predictor of value for Cladocera.

/pdf/factors-influencing-cladoceran-abundance-and-species-25gxav9oum.pdf

Factors influencing cladoceran abundance and species richness in brackish lakes in Eastern Spain

Benthic Chironomidae were studied in two shallow, brackish, eutrophic wetlands in Alicante province in eastern Spain (Levante lake in El Hondo Natural Park and Murtulas ponds in Santa Pola Natural Park). Core samples were taken monthly from eight points in each site from March to August 1999. Levante was more eutrophic, less saline, and held more and larger chironomid larvae than Murtulas. Larvae of six taxa were identified at Levante and five at Murtulas. Chironomus aprilinus and C. salinarius morphotypes dominated at Levante, whereas Tanytarsus spp. and C. salinarius dominated at Murtulas. In generalized linear models, there were significant effects of site, month, and site X month interactions on larval size at both family and taxon levels. On average, C. salinarius larvae were larger at MUR, probably due to a lower proportion of smaller instars and lower growth rates. Although the overall trend was for a reduction in mean larval size over time in both wetlands, mean size peaked in March at Levante and in May at Murtulas.

Seasonal variation in species composition and larval size of the benthic chironomid communities in brackish wetlands in southern alicante, spain

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31-49 mS cm -1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation-flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorophyll content indicated that EP was eutrophic and WP mesotrophic. Phytoplanktonic species richness and diversity were low in both ponds. Algal assemblages, in terms of biovolume, were mainly dominated by Dinophyceae in EP and by Cryptophyta in WP. The zooplankton community was dominated by Rotifers (Brachionus and Hexarthra), although Copepods and Ciliates were also important. Different water inputs to the ponds, partial drying in EP during the warm season with the subsequent higher increment of salinity, and the presence of dense populations of submerged macrophytes in WP, explain the differences in plankton communities found between the two ponds.

Environmental variables and planktonic communities in two ponds of El Hondo Wetland (SE Spain)

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Environmental variables and planktonic communities in two ponds of El Hondo Wetland (SE Spain)