Researchers uncover hidden seagrass species in the northwest Pacific

Seagrasses, foundational species in coastal ecosystems worldwide, are surprisingly few in documented diversity – with only about 70 species identified globally, despite their widespread distribution and ecological importance. Their high phenotypic plasticity within species makes precise classification challenging.

Against this backdrop, a research team led by Prof. Zhou Yi from the Institute of Oceanology of the Chinese Academy of Sciences, in collaboration with researchers from Germany's GEOMAR Helmholtz Center for Ocean Research Kiel and other institutions, has discovered cryptic speciation within Nanozostera japonica – a seagrass species common across the Northwest Pacific. The findings were published in New Phytologist.

N. japonica is rare among seagrasses as it's able to thrive in both temperate and tropical-subtropical coastal zones. Native to the Northwest Pacific, it spread to North America's Pacific coast in the early 20th century via oyster shipments. Its phenotypes vary sharply across geographic regions, and prior research using microsatellite markers revealed striking genetic differences between northern and southern populations – hinting that what is currently classified as N. japonica might include multiple species.

The study also identified hybrids between the clades in their contact zone, all of which are first-generation diploids or triploids – with no evidence of higher-order hybrids. This pattern strongly indicates reproductive isolation, a key marker of distinct species.

This marks the first time cryptic seagrass species have been identified using comprehensive population genomics. The study suggests seagrass diversity may be significantly underestimated, underscoring the need for more extensive population genomic research on these ecologically vital organisms.

From a press release by Li Yali, Chinese Academy of Sciences.