A Tight Interaction between the Native Seagrass Cymodocea nodosa and the Exotic Halophila stipulacea in the Aegean Sea Highlights Seagrass Holobiont Variations

Abstract

Seagrasses harbour bacterial communities with which they constitute a functional unit called holobiont that responds as a whole to environmental changes. Epiphytic bacterial communities rapidly respond to both biotic and abiotic factors, potentially contributing to the host fitness. The Lessepsian migrant Halophila stipulacea has a high phenotypical plasticity and harbours a highly diverse epiphytic bacterial community, which could support its invasiveness in the Mediterranean Sea. The current study aimed to evaluate the Halophila/Cymodocea competition in the Aegean Sea by analysing each of the two seagrasses in a zone where these intermingled, as well as in their monospecific zones, at two depths. Differences in holobionts were evaluated using seagrass descriptors (morphometric, biochemical, elemental, and isotopic composition) to assess host changes, and 16S rRNA gene to identify bacterial community structure and composition. An Indicator Species Index was used to identify bacteria significantly associated with each host. In mixed meadows, native C. nodosa was shown to be affected by the presence of exotic H. stipulacea, in terms of both plant descriptors and bacterial communities, while H. stipulacea remained almost unchanged. This study provided evidence of the competitive advantage of H. stipulacea on C. nodosa in the Aegean Sea and suggests the possible use of associated bacterial communities as a descriptor of native seagrass sustainability.

Undisturbed Posidonia oceanica meadows maintain the epiphytic bacterial community in different environments

“…Also, leaf total phenol content did not differ between the two sites and showed quite low values. Again, this indicates a healthy and comparable ecological status of the two meadows, as the phenol content is a seagrass descriptor is known to increase under stressed conditions (Dumay et al 2004 ; Migliore et al 2007 ; Rotini et al 2013a , 2013b ; Ceccherelli et al 2018 ; Mannino and Micheli 2020 ; Conte et al 2023 ). Plants from both Amathus and Akrotiri sites were found to contain half the total phenol content of their counterparts growing in the polluted area of the Limassol port (Conte et al 2021b ).…”

Impact of persistently high sea surface temperatures on the rhizobiomes of Zostera marina in a Baltic Sea benthocosms

“…Spirochaetacea are key degraders and decomposers of complex organic material commonly found in the seagrass rhizosphere (Wang et al., 2021). In the summer, Marinilabiliaceae were found to be the main degraders in Z. marina roots, as they can metabolize different forms of organic carbon (Conte et al., 2023; Tu et al., 2022). Unlike the ambient setup, that early temperature effect has also stimulated the sulfur cycle throughout the setup, with a stronger increase of sulfate reducers as temperature increases.…”

Decline of seagrass (Posidonia oceanica) production over two decades in the face of warming of the Eastern Mediterranean Sea

“…Similarly, the tropical seagrass H. stipulacea is expanding in the region facilitated by warming (Wesselmann et al ., 2021) and possibly faster than originally thought (Thibaut et al ., 2022). Although the species has not yet shown generalized signs of competition with P. oceanica (Winters et al ., 2020), the expansion of H. stipulacea at the expense of C. nodosa has been reported in Tunisia (Sghaier et al ., 2014) and the Aegean Sea (Conte et al ., 2023). Therefore, there is an imminent threat of further expansion and possible replacement of P. oceanica meadows of the Mediterranean Sea with other seagrass species that do not necessarily provide ecosystem services of similar magnitude (Campagne et al ., 2015; Mtwana Nordlund et al ., 2016).…”