Comparing the diversity of interstitial crustaceans at natural and artificial/degraded beaches in Okinawa

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Okinawa, a subtropical island in southern Japan, is well-known for its unique biodiversity, but relatively few studies have been conducted to monitor the effects of anthropogenic disturbances on marine ecosystems. Recent work has shown that disturbed artificial beaches have lower numbers and diversity of interstitial amphipods and isopods when compared to natural beaches. In this study, we collected interstitial crustaceans from six different sandy beaches around Okinawa-jima Island in May 2018, including heavily disturbed beaches near reclaimed land, artificial tourist beaches (=disturbed environment), and undisturbed, natural beaches far away from anthropogenic disturbances (=control) in order to more fully explore the range of diversity across a full spectrum of environments. We additionally utilized 18S ribosomal DNA barcodes and Automatic Barcode Gap Discovery (ABGD) to identify specimens to operational taxonomic units (OTUs). DNA barcodes showed 34 OTUs, and the method was more efficiently able to identify to the species-level, while morphological identifications often were only efficient to the genus or family level. In comparison with former data from 2015 in Okinawa, the overall numbers and diversity of amphipods and isopods were lower. Similar to previous results, natural beaches showed higher diversity in comparison with artificial/disturbed beaches. These results suggest that disturbances cause reductions in interstitial crustacean diversity.