Marinomyxa marina presence in a Halophila stipulacea meadow near a fish farm in south Evoikos Gulf (Greece)

Abstract

Halophila stipulacea (Forsskål) Ascherson [Order: Alismates, Family: Hydrocharitaceae] is an autochthonous seagrass of the Indo-Pacific and Red Sea; however, it has invaded two distinct geographical areas: the Mediterranean and Caribbean Sea. It is a known carrier of a phytomyxean endosymbiont which forms galls in the petioles of the leaves. In the present study we investigated its presence in a H. stipulacea meadow located proximal to a fish farm in the Southern Evoikos Gulf (Aegean Sea, Greece). Seagrass samples were collected seasonally from July 2021 until May 2022 from three sites of the meadow. A seasonal pattern was observed with the highest infection rates in summer (July), fewer in autumn (October) and absence of the marine phytomyxean species during winter (January) and spring (May). Moreover, pressure posed from the fish farm seemed to interfere with the gall abundances as statistically important differences in the infection rates were obvious. Morphological and anatomical traits of the formed galls confirmed that mature resting spores inside the galls are arranged in dyads. Molecular and phylogenetic analysis confirmed that the phytomyxean endosymbiont belonged to Marinomyxa marina and suggested minimal evolutionary divergence between invasive M. marina populations. In the Aegean Sea this is northernmost record of this phytomyxean endosymbiosis following the expansion of H. stipulacea.