 Diffuse hydrothermal fluids are used to inoculate tubes and vials containing nine different kinds of growth media, which are incubated at four different temperatures (click images for full size) |
Julie Huber
Marine Biological Laboratory
While many of the scientists on the Thompson are focused on understanding how submarine eruptions work from a geological perspective, some are interested in the effects of such eruptive activity on biological communities. Previous studies at mid-ocean ridge hydrothermal vents have shown that eruptions are important sources of energy for life, especially microbial life. As a refresher, all of life on earth is divided into 3 domains- Bacteria, Archaea, and Eukarya. Bacteria and Archaea, also called microbes, are single celled organisms with no true nucleus, no membrane-bound organelles, and they divide by binary fission. They are very very small- invisible to the naked eye- whereas most eukaryotes tend to be bigger things, like humans, tigers, shrimp, and fish. We have scientists on board who are interested in both the big stuff and the small stuff, and for all organisms, their survival is intimately connected to the volcanic activity. Microbial communities in particular thrive from the combined input of heat, water, and chemical energy in volcanic rocks. Chemicals like sulfur and hydrogen are being created at NW Rota, and microbes are harnessing that energy to make a living. And from our previous expeditions to NW Rota, it is clear that the microbes are having no problem making a good living!
 White microbial biofilms bathed in vent fluids make their living from the chemicals in the warm water and can also use rust colored iron oxides (seen here) as an energy source |
Diverse microbial communities are found everywhere on the volcano, including in the warm acidic vent fluids and coating all sorts of surfaces like rocks and sediments in microbial mats or biofilms. The vents at NW Rota are teeming with microbes, both archaea and bacteria, despite the harsh dynamic conditions created by the eruptive volcano. In fact, the microbial communities at NW Rota are more diverse and variable than microbes we find at other types of underwater volcanoes, like mid-ocean ridges or hot spot volcanoes. We’re still trying to understand why, but one hypothesis is that places like NW Rota have really complex hydrothermal chemistry and because of the extremely dynamic nature of the eruptive cycle, a lot of different niches or habitats are created for diverse microbial communities to exploit.
 Without the ability to bring a high-powered microscope to sea our only indicator for growth of microbes is “turbidity”, or cloudiness, of the growth medium. The vial on the left will contain somewhere between 107-108 cells per ml of fluid. |
In addition, eruptions are a great way to also sample what is happening within the seafloor, or in the subseafloor, because the fluids are forced out of the seafloor and when collected, provide a glimpse into organisms that normally live in the crust. Eruptive events are a great source of novel organisms and so when we can, we try to catch these events to also catch the novel microbes. We’ll spend the next 2 weeks trying to capture these diverse microbial communities and try to figure out who they are, how they make a living, and how they interact with and are impacted by the eruptive volcano.
Various types of filamentous microbial mat wave in the current on a vertical cliff near the summit of NW Rota-1. (no audio) |
