Benthic deep-sea fungi in submarine canyons of the Mediterranean Sea

Abstract

Fungi are ubiquitous components of microbial assemblages in aquatic ecosystems, but their quantitative relevance, ecological role and diversity in benthic deep-sea ecosystems are still largely unknown. Here, we investigated patterns and drivers of benthic fungal abundance, biomass and diversity from 200 to 1000 m depth in three submarine canyons of the Mediterranean Sea (Tricase, Crotone and Squillace canyons). The Crotone and Squillace canyons, which are close to the coast and influenced by river inputs, showed significantly higher fungal abundance, biomass and diversity (as operational taxonomic units, OTUs) compared with the Tricase canyon that was far from the coast and without nearby estuaries. Fungal biomass, abundance and diversity increased with increasing concentrations of carbohydrates, which in deep-sea sediments represent one of the most refractory organic compounds. Overall, a total of 1742 fungal OTUs, belonging to all fungal phyla known to date, were found and Ascomycota represented the dominant phylum. However, only 36% of the reads belonged to known genera. In particular, Tricase and Crotone canyons hosted the highest proportion of unknown fungal taxa, suggesting that deep-sea sediments can harbour a high number of novel fungal lineages. Our findings also reveal that fungal assemblage composition in the investigated canyons was influenced by trophic and thermohaline conditions, which may promote a high turnover diversity of benthic deep-sea fungal assemblages. Overall results reported here indicate that the submarine canyons of the Mediterranean Sea can represent hot-spots of abundant and highly diversified fungal assemblages and pave the way for a better understanding of the ecological role of fungi in the largest ecosystem on Earth.

Fungal communities in sediments along a depth gradient in the Eastern Tropical Pacific

“…Other less frequent fungal groups observed in this ecosystem were, Blastocladiomycota, LKM11, LKM15, Mucoromycota, and Zoopagomycota ( Figure 2B ). These results are consistent with earlier results obtained in deep-sea sediments from several parts of the planet confirming the general dominance of Ascomycota in deep-sea sediments together with the presence of Basidiomycota and Chytridiomycota in lower proportions (Li et al, 2016, 2019; Xu et al, 2016, 2019; Zhang et al, 2016; Nagano et al, 2017; Barone et al, 2018; Wang et al, 2019).…”

“…Therefore, it is crucial to study fungal diversity and ecology in deep-sea waters, for which there is a paucity of studies compared to the rest of the ocean. Detailed knowledge of deep-sea fungi is required to understand better the overall fungal contribution to marine food webs and biogeochemical cycles at the global scale (Manohar and Raghukumar, 2013; Barone et al, 2018; Drake and Ivarsson, 2018; Grossart et al, 2019; Román et al, 2019; Hassett et al, 2020).…”

“…In recent years, there has been a growing interest in studying fungal communities in deep-sea environments using culture-dependent and, to an increasing extent, culture-independent methods. Abundant fungal populations have been observed in a variety of deep-sea locations such as asphalt seeps in Sao Paulo Plateau (Nagano et al, 2017), methane seeps in the Kuroshima Knoll (Takishita et al, 2006), hydrothermal vents in the Mid-Atlantic Ridge (Le Calvez et al, 2009; Xu et al, 2017), sediments of the Peru Trench (Edgcomb et al, 2011), the East Indian Ocean (Zhang et al, 2014), the High Arctic (Zhang et al, 2015), the Mariana Trench (Xu et al, 2016, 2018), the Yellow Sea (Li et al, 2016), the Mediterranean Sea (Barone et al, 2018), the Yap Trench (Li et al, 2019), and subsurface sediments in Suruga-Bay (Nagano et al, 2016).…”

Microbial Community Structure and Functionality in the Deep Sea Floor: Evaluating the Causes of Spatial Heterogeneity in a Submarine Canyon System (NW Mediterranean, Spain)

“…At the regional scale, submarine canyons are among the most pervasive and dynamic deep-sea habitats (Ramirez-Llodra et al, 2010) that play the role of preferential particle-transport conduits and therefore act as drivers of trophic characteristics. However, because of the difficulties in accessing the deep seafloor, there is a fragmented available knowledge regarding the processes ruling the microbial community composition in these systems (Barone et al, 2018;Rzeznik-Orignac et al, 2018).…”

“…Submarine canyons thus offer heterogeneous habitats that are proved to host highly diverse fauna at different spatial scales, which are subjected to complex natural and anthropogenic processes (Sardà et al, 2009;De Leo et al, 2014;Ismail et al, 2018). Despite the increasing research focusing over the last decades on canyon ecosystems and the associated environmental functioning, the microbial assemblages thriving under these circumstances are still being unveiled (Barone et al, 2018;Celussi et al, 2018;Rzeznik-Orignac et al, 2018), and their response to both canyons' natural and anthropogenic processes remains poorly known. Remarkably, very few studies have aimed at evaluating how different sedimentation conditions (e.g., OM accumulation) may alter the microbial communities, the first compartment of benthic food web, along submarine canyons (Danovaro et al, 2000;Goffredi and Orphan, 2010).…”