ITS DNA Barcoding Reveals That Halophila stipulacea Still Remains the Only Non-Indigenous Seagrass of the Mediterranean Sea

Catalina A García-Escudero,Eugenia T Apostolaki,Vasilis Gerakaris,Costas S Tsigenopoulos,Alexandros Tsakogiannis

doi:10.3390/d14020076

Catalina A García-Escudero, Eugenia T Apostolaki + Show 3 more

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https://doi.org/10.3390/d14020076

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Abstract

Non-indigenous species (NIS) are one of the major threats to the native marine ecosystems of the Mediterranean Sea. Halophila stipulacea was the only exotic seagrass of the Mediterranean until 2018, when small patches of a species morphologically identified as Halophila decipiens were reported in Salamina Island, Greece. Given the absence of reproductive structures during the identification and the taxonomic ambiguities known to lead to misidentifications on this genus, we reassessed the identity of this new exotic record using DNA barcoding (rbcL, matK and ITS) and the recently published taxonomic key. Despite their morphologic similarity to H. decipiens based on the new taxonomic key, the specimens showed no nucleotide differences with H. stipulacea specimens (Crete) for the three barcodes and clustered together on the ITS phylogenetic tree. Considering the high species resolution of the ITS region and the common morphological variability within the genus, the unequivocal genetic result suggests that the Halophila population found in Salamina Island most likely corresponds to a morphologically variant H. stipulacea. Our results highlight the importance of applying an integrated taxonomic approach (morphological and molecular) to taxonomically complex genera such as Halophila, in order to avoid overlooking or misreporting species range shifts, which is essential for monitoring NIS introductions.

Highlights

The natural ranges of species are inherently dynamic, but in recent decades globalization and climate change have accelerated the pace of change by facilitating the introduction of species outside their natural ranges [1,2,3]
Based on the compiled information of the current taxonomic key of the genus Halophila (Kuo, 2020) [62] and the two previous keys, Phillips & Mehez (1988) [66] and Kuo & Den Hartog (2001) [63], the vegetative morphological characters of the specimens found in Salamina Island (Halophila sp.) match better with H. decipiens’s diagnostic characters than to those of H. stipulacea, especially regarding the low number and type of cross-veins and the structure of the scales (Table 2 and Figure 1)
The Halophila specimens from Salamina Island, morphologically described as H. decipiens (Halophila sp.) [39], did not show any nucleotide differences in the three DNA barcodes (ITS, rbcL, and matK) when compared to the H. stipulacea specimens from Crete, a population established in the Mediterranean Sea many years ago, suggesting that the specimens belong to the same species

Summary

Introduction

The natural ranges of species are inherently dynamic, but in recent decades globalization and climate change have accelerated the pace of change by facilitating the introduction of species outside their natural ranges [1,2,3]. The vast majority occur in the eastern subregion and probably entered the basin through the Suez Canal, which since 1869 connects the Mediterranean Sea with the IndoPacific region [10,11,12] This artificial passage, combined with the high volume of shipping routes, aquaculture, aquarium trade [12,13], and recent warming of Mediterranean waters due to climate change, makes the basin vulnerable to the introduction of NIS [14,15]. M.C.; Barbieri, F.; Bianchi, C.N. New Record of the Alien Seagrass Halophila stipulacea (Hydrocharitaceae) in the Western Mediterranean: A Further Clue to Changing Mediterranean Sea Biogeography. Occurrence of the Seagrass Halophila stipulacea (Hydrocharitaceae) in the Southern Mediterranean Sea. Bot. Distribution of the Seagrass Halophila stipulacea: A Big Jump to the Northwestern Mediterranean Sea. Aquat.

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