The potential role of temperate Japanese regions as refugia for the coral Acropora hyacinthus in the face of climate change

Aki Nakabayashi,Yuko F Kitano,Hiroaki Aizawa,Akira Iguchi,Hiroya Yamano,Nina Yasuda,Satoshi Nagai,Kosuke M Teshima,Takehisa Yamakita,Sylvain Agostini,Takashi Nakamura

doi:10.1038/s41598-018-38333-5

Abstract

As corals in tropical regions are threatened by increasing water temperatures, poleward range expansion of reef-building corals has been observed, and temperate regions are expected to serve as refugia in the face of climate change. To elucidate the important indicators of the sustainability of coral populations, we examined the genetic diversity and connectivity of the common reef-building coral Acropora hyacinthus along the Kuroshio Current, including recently expanded (<50 years) populations. Among the three cryptic lineages found, only one was distributed in temperate regions, which could indicate the presence of Kuroshio-associated larval dispersal barriers between temperate and subtropical regions, as shown by oceanographic simulations as well as differences in environmental factors. The level of genetic diversity gradually decreased towards the edge of the species distribution. This study provides an example of the reduced genetic diversity in recently expanded marginal populations, thus indicating the possible vulnerability of these populations to environmental changes. This finding underpins the importance of assessing the genetic diversity of newly colonized populations associated with climate change for conservation purposes. In addition, this study highlights the importance of pre-existing temperate regions as coral refugia, which has been rather underappreciated in local coastal management.

Highlights

Coral reef ecosystems harbour high biodiversity, supporting almost 30% of marine coastal species[1]
Population connectivity and relatively high genetic diversity are crucial for a population to expand and persist under climate change[7]; these characteristics are important for the populations in potential refugia
Because we are interested in the genetic connectivity and diversity of the lineages that have recently expanded in temperate regions, we focused on one lineage found in both temperate and subtropical regions

Summary

Introduction

Coral reef ecosystems harbour high biodiversity, supporting almost 30% of marine coastal species[1]. Winter water temperature has risen by 1.45 °C over the last 100 years in the temperate Kuroshio Current region in Japan (http://www.data.jma.go.jp/gmd/kaiyou/data/shindan/a_1/japan_warm/japan_warm.html), causing coral expansion and producing potential coral refugia at the edges of their distribution ranges[3]. While such temperate region can be potential coral refugia, temperate peripheral populations may suffer from reduced genetic diversity due to small population sizes and isolation[8]. A. hyacinthus is one of the key reef-building species on tropical reefs[14] and can represent as much as 36% of the coral coverage in some high-latitude areas[15] These ecological features of this species are suitable for comparing the genetic diversity and connectivity of populations among temperate and subtropical regions. The region was split along this line because the biogeography of this region is often split between Yakushima and the Amami Islands, and the Kuroshio Current passes through this region

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