Diversity and phylogeny of seagrasses in Singapore

Abstract

Seagrasses are vital to the health of coastal marine ecosystems and are threatened with habitat destruction as well as other anthropogenic pressures, but their diversity and taxonomy remain poorly studied. Seagrasses can exhibit large morphological variation in response to environmental variables, resulting in field observations being unreliable for identification. Therefore, molecular phylogenetic approaches can be informative in delimiting and identifying seagrass species. In this study, molecular phylogenetic analyses and morphological examinations of nearly 100 seagrasses collected from six sites distributed across Singapore’s northern and southern coasts were integrated to assess their diversity and phylogeny. The nuclear ITS and plastid matK loci were amplified and sequenced for phylogenetic analyses. Our analyses and morphological examinations recovered 10 well-supported lineages corresponding to 10 seagrass species in Singapore (Thalassia hemprichii, Enhalus acoroides, Halophila beccarii, Halophila spinulosa, Halophila major, Halophila ovalis, Halodule uninervis, Oceana serrulata, Syingrodium isoetifolium, and Cymodocea rotundata), including one new local record of Halophila major. Although Halophila ovata, Halodule pinifolia and Halophila decipiens are reflected in historical local records, they were not found in the field, hence raising the possibility that these species could have been locally extirpated. The molecular markers used here, ITS and matK, could clearly delineate most seagrass species but some species-level clades within Halodule and Halophila remain unresolved. Continued work on seagrass phylogenetics will help resolve species complexes and provide more precise species richness estimates, which are critical for seagrass meadow conservation and management.