Abstract
During recent decades, over 40% of Japanese estuarine tidal flats have been lost due to coastal developments. Local populations of the saltmarsh sesarmid crab Clistocoeloma sinense, designated as an endangered species due to the limited suitable saltmarsh habitat available, have decreased accordingly, being now represented as small remnant populations. Several such populations in Tokyo Bay, have been recognised as representing distributional limits of the species. To clarify the genetic diversity and connectivity among local coastal populations of Japanese Clistocoeloma sinense, including those in Tokyo Bay, mitochondrial DNA analyses were conducted in the hope of providing fundamental information for future conservation studies and an understanding of metapopulation dynamics through larval dispersal among local populations. All of the populations sampled indicated low levels of genetic diversity, which may have resulted from recent population bottlenecks or founder events. However, the results also revealed clear genetic differentiation between two enclosed-water populations in Tokyo Bay and Ise-Mikawa Bay, suggesting the existence of a barrier to larval transport between these two water bodies. Since the maintenance of genetic connectivity is a requirement of local population stability, the preservation of extant habitats and restoration of saltmarshes along the coast of Japan may be the most effective measures for conservation of this endangered species.
Highlights
Many estuarine ecosystems worldwide have been severely disrupted by human activities, such as overexploitation, pollution and land reclamation [1]
Because the genetic structures of populations at the limits of geographical distribution are generally characterized by increased genetic isolation and differentiation [10], the conservation of such populations requires an understanding of gene flow among edge and central populations, and their connectivity through larval transport
Low Genetic Diversity All populations of the endangered sesarmid crab Clistocoeloma sinense in estuarine saltmarshes located from central Honshu to Kyushu showed low levels of genetic diversity, as measured by haplotype and nucleotide diversities, compared with those of other intertidal brachyuran crabs (Table 5)
Summary
Many estuarine ecosystems worldwide have been severely disrupted by human activities, such as overexploitation, pollution and land reclamation [1]. In Japan, more than 40% of tidal flats, including estuarine in saltmarshes, have been lost, mainly during the latter half of the 20th century [2]. The destruction of estuarine mudflats and saltmarshes by land reclamation have resulted in the reduction of local populations of many mudflat/saltmarsh-specific species [3]. Large-scale reclamation of tidal flats and saltmarshes along the entire coastline of Tokyo Bay, conducted during the late 1960s and early 1970s [4], resulted in the loss of most of the saltmarshes in the high intertidal zone by the end of the 1970’s. Most mudflat/saltmarsh-specific benthic species in Tokyo Bay have since become extinct or endangered [5]. Tokyo Bay, representing the northern and easternmost limits of the species geographical distribution, is separated by a distance of ca. Because the genetic structures of populations at the limits of geographical distribution are generally characterized by increased genetic isolation and differentiation [10], the conservation of such populations requires an understanding of gene flow among edge and central populations, and their connectivity through larval transport
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