Ferrous iron‐ and ammonium‐rich diffuse vents support habitat‐specific communities in a shallow hydrothermal field off the Basiluzzo Islet (Aeolian Volcanic Archipelago).

Abstract

Ammonium- and Fe(II)-rich fluid flows, known from deep-sea hydrothermal systems, have been extensively studied in the last decades and are considered as sites with high microbial diversity and activity. Their shallow-submarine counterparts, despite their easier accessibility, have so far been under-investigated, and as a consequence, much less is known about microbial communities inhabiting these ecosystems. A field of shallow expulsion of hydrothermal fluids has been discovered at depths of 170-400 meters off the base of the Basiluzzo Islet (Aeolian Volcanic Archipelago, Southern Tyrrhenian Sea). This area consists predominantly of both actively diffusing and inactive 1-3 meters-high structures in the form of vertical pinnacles, steeples and mounds covered by a thick orange to brown crust deposits hosting rich benthic fauna. Integrated morphological, mineralogical, and geochemical analyses revealed that, above all, these crusts are formed by ferrihydrite-type Fe oxyhydroxides. Two cruises in 2013 allowed us to monitor and sampled this novel ecosystem, certainly interesting in terms of shallow-water iron-rich site. The main objective of this work was to characterize the composition of extant communities of iron microbial mats in relation to the environmental setting and the observed patterns of macrofaunal colonization. We demonstrated that iron-rich deposits contain complex and stratified microbial communities with a high proportion of prokaryotes akin to ammonium- and iron-oxidizing chemoautotrophs, belonging to Thaumarchaeota, Nitrospira, and Zetaproteobacteria. Colonizers of iron-rich mounds, while composed of the common macrobenthic grazers, predators, filter-feeders, and tube-dwellers with no representatives of vent endemic fauna, differed from the surrounding populations. Thus, it is very likely that reduced electron donors (Fe and NH ) are important energy sources in supporting primary production in microbial mats, which form a habitat-specific trophic base of the whole Basiluzzo hydrothermal ecosystem, including macrobenthic fauna.

Banded Iron Travertines at the Ilia Hot Spring (Greece): An interplay of biotic and abiotic factors leading to a modern Banded Iron Formation analogue?

“…This conclusion is supported by the presence of fabrics showing a close association of ferrihydrite with filamentous textures resembling sheaths formed by Zetaproteobacteria (Figures g and g,h). They are covered with ferrihydrite particles, and are strikingly similar to the structures described in other settings exhibiting the same organisms (Bortoluzzi et al., ; Handley et al., ; Takashima et al., ). In submarine or continental hydrothermal systems, ferrihydrite is interpreted as precipitated by sheathed or stalked iron oxidizers.…”

“…(); *4 = Bortoluzzi et al. () (DFS1); *5 = Kilias et al. () (NA014‐027 Champagne active mound‐2); *6 = Pichler and Veizer () (Vents 1–3); *7 = Athanasoulis et al.…”

“…Regarding iron, Ilia's hydrothermal fluid shows higher concentrations than the terrestrial hot springs of Japan (Takashima & Kano, ; Takashima et al., ) and the hydrothermal vent from Tutum Bay (Papua New Guinea; Pichler & Veizer, ). However, iron concentrations are lower when compared to the Basiluzzo Islet (Italy; Bortoluzzi et al., ) and Kolumbo (Greece; Kilias et al., ) submarine vents. Hence, Ilia hot spring shares some similar physicochemical characteristics with the fluids of the above‐mentioned areas.…”

“…Active hydrothermal iron-rich deposits are among the targets of this search. They can be found in terrestrial environments, that is, iron-rich thermogenic travertines (Kanellopoulos, Mitropoulos, Valsami-Jones, & Voudouris, 2017;Takashima & Kano, 2005;Takashima, Okumura, Nishida, Koike, & Kano, 2011) and in submarine hydrothermal environments (Bortoluzzi et al, 2017;Kilias et al, 2013;Pichler & Veizer, 1999). In these systems, the presence of microbial activity is most often identified at redox interfaces and has been suggested to play an active role in the formation of iron minerals such as iron oxides (Kappler & Newman, 2004;Konhauser, 1998;Widdel et al, 1993).…”

Why Is Crustal Underplating Beneath Many Hot Spot Islands Anisotropic?

“…This vented fluid has reducing chemistry, marked by ferrous‐iron Fe 2+ , that is metabolized by iron‐oxidizing Zetaproteobacteria to ferric‐iron Fe 3+ and deposited as iron‐oxyhydroxide layers where the vent fluids meet the O 2 ‐rich ambient seawater. Loihi is only one locale for Zetaproteobacteria; similar diffuse‐vent ecosystems have been discovered globally, proximal to hot sulfide‐rich vent systems (Emerson & Moyer, ), near hot spots (Johannessen et al, ), mid‐ocean ridges (Scott et al, ), and island arc volcanoes (Bortoluzzi et al, ; Ristova et al, ). Bach () estimates that Fe‐oxidizing bacteria represent roughly 10% of the sedimentary deep biosphere.…”