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

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 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.

Validated Inventories of Non-Indigenous Species (NIS) for the Mediterranean Sea as Tools for Regional Policy and Patterns of NIS Spread

“…On the other hand, one characteristic example of a macroalgal species which was revised in the current inventory is Halophila decipiens. The seagrass H. decipiens was reported with a single population in Salamina, Greece in 2018 [97] but its identification was based only on vegetative morphological characters; a subsequent study employing DNA barcoding demonstrated that the Greek population actually corresponds to a morphologically variant H. stipulacea [98], hence H. decipiens was removed from the Greek national inventory and consequently from the Mediterranean baseline. Despite ongoing progress in elucidating the identity and origin of many macroalgal cryptic species [99], there is a clear need for more molecular and phylogeographic studies of this species group.…”

Tropicalization of seagrass macrophytodetritus accumulations and associated food webs

“…In Cannes harbor (NW Mediterranean Sea), H. stipulacea was probably introduced via big yachting coming by Suez Canal and are establishing stable population which could indicate that conditions are now more favorable for long-term population establishment (Thibaut et al, 2022). H. stipulacea is presently the only non-native seagrass in the Mediterranean Sea (Garcıá-Escudero et al, 2022). It generally colonizes habitats devoid of native seagrass, forms mixed meadows with C. nodosa (Winters et al, 2020), or colonizes dead matte of P. oceanica (Thibaut et al, 2022).…”