Sediment microbial communities in a Cymodocea nodosa seagrass meadow

Markovski, Marsej (2025) Sediment microbial communities in a Cymodocea nodosa seagrass meadow. Doctoral thesis, University of Zagreb, Faculty of Science.

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Abstract

The presence of seagrass in marine environments influences surface sediments and creates specific environmental conditions that support diverse and abundant sediment microbial communities. However, the decline of seagrass meadows of various species has been documented worldwide, including that of Cymodocea nodosa, a common seagrass species in the Mediterranean Sea. In the Bay of Saline, located in the northern Adriatic Sea, a decline of a Cymodocea nodosa meadow was observed during its monthly status assessment from July 2017 to October 2018. To determine the response of sediment microbes to seagrass meadow decline, surface sediments were collected from two sites during that period, one without vegetation and one with the declining seagrass meadow. The microbial response was assessed by determining community composition and metabolic profile. In addition, the environmental conditions in the sediment were assessed and changes after the onset of meadow decline were detected, such as an accumulation of hydrogen sulphide. Despite these changes, no clear temporal succession of the microbial community in the sediment was observed. Instead, the communities were stratified by sediment depth and exhibited distinct community composition between sites. The bacterial community was mainly comprised of Desulfobacterota, Gammaproteobacteria, Bacteroidota, Chloroflexi, Planctomycetota, and Campylobacterota, while the archaeal community was dominated by Nanoarchaeota, Thermoplasmatota, Crenarchaeota, and Asgardarchaeota. Functional analysis based on microbial profiles revealed that these communities degrade complex sugars and proteins, producing acetate, formate, and ethanol by fermentation, thereby supporting dissimilatory sulphate reduction. Before the seagrass decline, notable differences in the metabolic profiles were observed between sites. However, during the decline, the profiles converged, with those of the nonvegetated site resembling the ones of the Cymodocea nodosa meadow sediment. These results indicate that while the microbial communities in the seagrass meadow sediments remain stable in composition and function during the decline, adjacent communities shift their metabolic profiles, highlighting the broader ecological influence of the decline of seagrass meadows.

Item Type:

Thesis (Doctoral thesis)

Uncontrolled Keywords:

sediment microbial communities; microbial community composition; microbial metabolic profile; Cymodocea nodosa; seagrass meadow decline; northern Adriatic Sea

Subjects:

NATURAL SCIENCES > Biology > Microbiology
NATURAL SCIENCES > Interdisciplinary Natural Sciences > Marine Science

Divisions:

Center for Marine Research

Projects: