Saline inland and coastal waterbodies are valuable habitats that deserve attention for the protection of their unique submerged macrophyte beds that render the water clear, stabilize sediments and provide a habitat for high biomasses of invertebrates as food for waterfowl. The 'continental seagrass' Ruppia has the widest salinity tolerance among the submerged macrophytes and occurs in a wide variety of saline saltmarsh pond and lagoon systems. Although two cosmopolitan species Ruppia maritima and Ruppia cirrhosa are recognized in Europe and Ruppia drepanensis in the western Mediterranean, their diversity and distribution are not well known. This previously held traditional idea that there are only two widespread Ruppia species suggests a uniform and very homogenized population structure following the hypothesis of long-distance-dispersal through strong bird-mediated dispersal events. Therefore, the Ruppia chloroplast DNA diversity was investigated along a more than 1,000 km transect of the Iberian Peninsula. We studied 492 individuals from 11 wetland areas (17 ponds) and sequenced a 1,753-bp length of seven chloroplast introns. Eight haplotypes represented at least four distinct groups or taxa which is higher than commonly accepted. Six wetland areas contained more than one haplotype and within-pond diversity occurred within distances as small as 30 m (5 out of 17 cases). This underlines the importance of single waterbodies for harbouring haplotypic diversity in Ruppia. Unique haplotypes were observed in four wetland areas and R. maritima was detected only from a low salinity pond, suggesting the species might be more rare than previously accepted. The present results tend to minimize an overall effect of strong bird-mediated dispersal. This emphasizes the role of regional pond habitat diversity for the preservation of Ruppia taxa and their unique haplotype diversity in extreme saline habitats.
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