Dr. Alexander Bochdansky | Old Dominion (hosted by Astrid Schnetzer)

Microbial ecology of deep-sea particles

Abstract:
The deep sea (> 1000 m depth) is by far the largest environment on Earth. Macroscopic particles in the water column (also termed marine snow) appear to play an important ecological role in overall ecosystem processes in the deep sea as they provide abundant resources for microbes in an otherwise desert-like water column.  Using a holographic microscope custom-made for the deep sea, we found that a large proportion (~30 % by numbers and more by volume) of marine snow is composed of transparent, loosely-packed particles containing a large amount of invisible and sticky organic material that holds smaller particles together. These loosely-packed amorphous particles seem to be neutrally buoyant or sink only slowly because they are exceedingly rare in deep-sea sediment traps, which in turn are dominated by dense, fast-sinking algal aggregates, and fecal pellets. We collected marine snow of the deep sea by gentle gravity filtration directly from Niskin bottles, which is a method unbiased by their respective settling velocities. In these particles, the composition of microbes was strikingly different from that of the surrounding water. The two main groups (i.e., the fungi and labyrinthulomycetes) are very different from bacteria and are known to be major decomposers of dead material.  These and many other findings during the last ten years challenge many traditional methods and models that have been employed in the deep sea.