Expansion of Halophila stipulacea in parallel with declines of native seagrasses in the eastern Mediterranean Sea

Abstract

Seagrasses native to the Mediterranean Sea are anticipated to be adversely affected by climate warming, while the invasive tropical seagrass species Halophila stipulacea is projected to proliferate and alter the region's underwater seascape. Despite the significant implications of this transition, it is surprisingly rare to include H. stipulacea in long-term monitoring programs across the Mediterranean. In July 2023, we conducted a follow-up study at a seagrass meadow in Limassol, Cyprus, which in 2017 was home to two native seagrass species, Cymodocea nodosa and Posidonia oceanica, alongside the invasive H. stipulacea. We assessed the seagrass cover of all present species and examined the characteristics of the H. stipulacea meadow, comparing our findings with data from 2017. Our results indicated a total loss of both native seagrass species, while H. stipulacea nearly doubled its coverage and exhibited substantial increases in shoot density, as well as above- and below-ground biomasses. Although our study is limited in scope, it supports earlier predictions regarding the anticipated transformations in the eastern Mediterranean's underwater landscape. This study highlights the urgent need to incorporate H. stipulacea into long-term seagrass monitoring efforts in the Mediterranean.