Delineating seagrass species in the genera Halodule and Halophila from Tanzanian coastal waters using ITS and rbcL DNA barcoding

Abstract

The seagrass species in Halodule and Halophila may for several reasons be considered as taxonomic complexes. They show close evolutionary relationships, morphological plasticity and share similar features making misidentifications likely when morphological identification is applied. In Tanzanian coastal waters, there is some uncertainty about the identity of members of Halodule, particularly the existence of Halodule wrightii and the species composition of the Halophila ovalis complex. This study used morphology as well as internal transcribed spacer (ITS1 and ITS2) and ribulose‐bisphosphate carboxylase (rbcL) DNA barcoding to identify species of Halodule and Halophila. Seagrass samples were collected during low spring tides, from Tanzania's coastal waters of Tanga, Dar es Salaam, Mtwara, Mafia Island and Unguja Island, from August 2020 to February 2022. Morphological diagnosis, phylogenetic analysis and evolutionary divergences inferred from the ITS gene supported the identification of five species, namely Halophila ovalis, H. minor and H. stipulacea, with the first two forming the H. ovalis complex; as well as Halodule uninervis and H. pinifolia. It is the first time that H. pinifolia is reported in Tanzania. This is the first study reporting the delineation of seagrass species in East African coastal waters using DNA barcoding coupled with morphology.