Abstract
The east Taiwan Strait is largely fringed by sandy and muddy habitats. However, a massive algal reef made of crustose coralline algae has been found along the coast off Taoyuan city in northwestern Taiwan. The porous structure of Taoyuan Algal Reef harbors high abundance and diversity in marine organisms, including the ferocious reef crab, Eriphia ferox. Such a pivotal geographic location and unique ecological features make Taoyuan Algal Reef a potential stepping stone connecting biotic reefs in the east Taiwan Strait, South China Sea to the south, and even the high latitude of Japan to the north. In this study, we examined the population connectivity and historical demography of E. ferox by analyzing mitochondrial cytochrome oxidase I (COI) fragments of 317 individuals sampled from 21 localities in the northwestern Pacific. Our analyses of haplotype network and pairwise FST comparisons revealed a lack of phylogeographical structure among E. ferox populations, implying the existence of a migration corridor connecting the South and East China Seas through the east Taiwan Strait. Multiple lines of evidence, including significant values in neutrality tests, unimodally shaped mismatch distributions, and Bayesian skyline plots elucidated the rapid population growth of E. ferox following the sea-level rise after Last Glacial Maximum (ca. 2–10 Ka). Such demographic expansion in E. ferox coincided with the time when Taoyuan Algal Reef started to build up around 7,500 years ago. Coalescent migration analyses further indicated that the large and continuous E. ferox population exclusively found in Datan Algal Reef, the heart of Taoyuan Algal Reef, was a source population exporting migrants both northward and southward to the adjacent populations. The bidirectional gene flow should be attributed to larval dispersal by ocean currents and secondary contact due to historical population expansion. Instead of serving as a stepping stone, our results support that Taoyuan Algal Reef is an essential population source for biotic reef-associated species along the east Taiwan Strait, and highlight the importance of conserving such a unique ecosystem currently threatened by anthropogenic development.
Highlights
The Taiwan Strait, bounded between southeastern China and Taiwan, is a shallow passage bridging the South China Sea (SCS) and the East China Sea (ECS)
We analyzed 317 partial mtCOI sequences of the ferocious reef crab Eriphia ferox collected from 21 sites, spanning nearly 4,500 km (Euclidean distance) within the northwestern Pacific
Our analyses of the haplotype network and pairwise FST comparisons demonstrated a lack of phylogeographical structure in E. ferox populations, implying the existence of a migration corridor connecting the South and East China Seas (SCS and ECS) through the east Taiwan Strait
Summary
The Taiwan Strait, bounded between southeastern China and Taiwan, is a shallow passage bridging the South China Sea (SCS) and the East China Sea (ECS). The interplay of paleoclimate and distinct topographical features of the Taiwan Strait has subsequently shaped the distribution patterns and genetic diversity of extant marine organisms in the northwestern Pacific (Ni et al, 2014 and references therein). During glacial periods throughout the Pleistocene (2.6 Ma– 11.7 ka), the recurrent desiccation and exposure of land mass in the Taiwan Strait culminated in transient disconnections between SCS and ECS basins (Wang, 1999; Kimura, 2000; Ludt and Rocha, 2015). As our current understanding of marine phylogeography in the northwestern Pacific exclusively relies on studies conducted along the Chinese coast (reviewed in Ni et al, 2014), such cross-strait divergence highlights the necessity to explore the role of the uninvestigated west coast of Taiwan
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