Microbial diversity and its role in the resilience of large brown seaweeds

Master Thesis subject (30 ECTS)
Human activities are causing environmental and ecological changes of global significance. By a variety of direct and indirect mechanisms, anthropogenic pressures on ecosystems contribute to the loss of biodiversity, homogenization of biota and alteration of ecosystem processes, with profound consequences for ecosystem services and human economic and social activities. Coastlines are no exception to this global trend. Coastlines harbor some of the most ecologically and socio-economically significant ecosystems on the planet. They play a crucial role in maintaining the health of the planet's ecosystems and serve as a valuable current and future food source for humankind. Ironically, the great wealth of coastal areas, whether in terms of fishing, tourism, international trade, or natural resources, makes the seeds of their own destruction. Europe, with 86 % of its coasts at either high or moderate risk, ranks first of the regions whose coastal ecosystems are most threatened by degradation. Here we focus on microbial diversity associated with large brown algae, because the causes, patterns and consequences of changes in biodiversity at this level are still largely unexplored. Large, brown, canopy-forming seaweeds are foundation species that control structural complexity, productivity, nutrient cycling and high associated biodiversity in temperate rocky reefs. They constitute an important source of substrata for microbial colonization. Their three-dimensional structure offers critical surface area in benthic marine habitats and provides temporary or permanent shelters and sediment traps. They provide a protected micro-niche for microbial colonisation and reproduction and release exudates that may serve as source of carbon for heterotrophic bacteria living on their surface. In turn, bacteria can directly and indirectly affect the morphogenesis and growth of their host seaweeds. They produce plant growth-promoting substances, quorum sensing signalling molecules, and bioactive compounds that are responsible for normal development and growth of seaweeds. Also, bioactive molecules of associated bacteria determine the presence of other bacterial strains on seaweeds, and can protect the host from harmful entities present in the pelagic realm. Working with specimens of large brown seaweeds from the Mediterranean (namely retracting species of Cystoseira, Fucus virsoides), the student will describe the diversity of the microbial communities associated with model fucoid algae subject to different stress levels. You will compare the microbiome diversity of the algae under a variety of environmental and human pressures. The sampling will be replicated at different locations and sites along the coasts of Italy, selected to cover a range of different levels of stressors (i.e. highly urbanised sites where severe canopy regression is in progress vs more pristine sites with dense stable stands of Cystoseira) and will be designed to: 1) identify the diversity of species associated; 2) their spatial and temporal scales of variation; and 3) the relationships with important environmental (e.g. hydrodynamics) and anthropogenic (e.g. nutrient concentration, sediment levels, or other pollutants) stressors that could affect the microbial community both directly or indirectly, by influencing the physiological status of the seaweeds. Bacterial diversity analyses will be carried out using 16S rRNA gene amplicon sequencing using NGS platforms. The healthy status of the seaweeds will be quantified by measuring parameters such as density of fronds, growth, productivity and photosynthetic efficiency (by using PAM fluorometry). The information will allow developing testable models relating the microbial diversity with environmental conditions and pressures, to be tested in subsequent experiments.
interest in microbiology, marine ecology, basic phycology knowledge
Number of students: 
academic year: 
Contact person email: 
contact person first name: 
Olivier De Clerck
Other people involved: 
Laura Airoldi (Univ. Bologna)
Reference Number: RP-36322