A DNA barcode library for mangrove gastropods and crabs of Hong Kong and the Greater Bay Area reveals an unexpected faunal diversity associated with the intertidal forests of Southern China

Abstract

Background Mangroves are tropical and subtropical intertidal forests colonising sheltered coasts across the world. They host a unique faunal community, dominated by brachyuran crabs and gastropods. These invertebrates strongly contribute to the functionality of the entire forest. The reliable assessment of mangrove faunal diversity is, thus, a crucial step for efficient management and conservation plans, but it is hindered by difficulties in species identification. Here we provide a verified DNA barcode library for brachyuran crabs and gastropods inhabiting the mangroves of the Greater Bay Area, Southern China. In particular, we collected and morphologically identified 1100 specimens of mangrove associated brachyuran crabs and gastropods. The partial sequences of the mtDNA cytochrome oxidase subunit I gene were obtained from 275 specimens. Barcode sequences were then used to delineate Molecular Operational Taxonomic Units (MOTUs), employing three different delimitation methods: the automatic barcode gap discovery (ABGD) method, the general mixed Yule coalescent (GMYC) model and a Bayesian implementation of the Poisson tree processes (bPTP) model. Results By integrating DNA barcodes with morphology, we identified 44 gastropod species and 58 brachyuran species associated with Hong Kong mangroves, with five and seven new records, for gastropods and crabs, respectively, for the Greater Bay Area. The delineation of MOTUs based on barcode sequences revealed a strong congruence between morphological and molecular identification for both taxa, showing the high reliability of the barcode library. Conclusions This study provides the first reference barcode library for mangrove-associated macrobenthic fauna in the Greater Bay Area and represents a reliable tool to management and conservation plans. Our molecular analyses resolved long lasting taxonomic misidentifications and inconsistencies and updated the knowledge on the geographical distribution of Asian mangrove associated fauna, ultimately highlighting a level of biodiversity higher than previously thought for Southern China.

The Coral Triangle and Strait of Malacca are two distinct hotspots of mangrove biodiversity

“…Following the clustering of specimens based on analyses of mitochondrial and nuclear DNA sequences, anatomical examinations of each species were done, and additional museum specimens could be identified. Geographic records from China and Japan are included in the geographic distributions of species based on GenBank sequences that cluster with the taxa identified in our taxonomic studies 101 – 104 . Geographic distributions of the onchidiids outside the Indo-West Pacific are detailed in Goulding et al 46 .…”

Species-specific gill’s microbiome of eight crab species with different breathing adaptations

“…Our six intertidal model brachyuran species belong to three families characterized by different breathing adaptations. Tubuca arcuata is a fiddler crab that inhabits the intertidal areas sheltered by the canopy of mangrove trees, while the ghost crab Ocypode ceratophthalmus digs deep burrows on muddy-sandy beaches 46 . Both species belong to the family Ocypodidae, they are active in air at low tide and evolved a branchiostegal lung, an area of improved blood circulation that lines the branchiostegal chamber where their blood can exchange oxygen with air 11 , 13 .…”

Barcoding a glass eel migration: a snapshot of taxa migrating upstream in the Palu River, Central Sulawesi, Indonesia

“…One reason for this knowledge gap is that the early stages of many diadromous taxa recruiting to freshwater are hard to identify to species level, and sometimes even to higher taxonomic levels, based on morphological methods alone. This is the case for anguillid glass eels [15] and other fishes [18,19] as well as invertebrates such as crustaceans [20] and molluscs [21,22].…”

“…The advances over recent decades in molecular biology include the development of DNA barcoding techniques, enabling identification of a specimen from the nucleotide sequence of a molecular marker; this is a specified region of the genome (barcode) which is highly conserved within a given taxon (ideally species) but differs between taxa [23,24]. This method is increasingly used for identifying specimens that are challenging or impossible to identify based on morphology, such as cryptic species and larval or juvenile stages [18][19][20][21][22]25], including anguillid glass eels [15]. The main limitation of DNA barcoding is that identification depends on the availability of a reference sequence for the taxon being identified in the public nucleotide sequence databases [24].…”