Dragon kings of the deep sea: marine particles deviate markedly from the common number-size spectrum

Abstract

Particles are the major vector for the transfer of carbon from the upper ocean to the deep sea. However, little is known about their abundance, composition and role at depths greater than 2000 m. We present the first number-size spectrum of bathy- and abyssopelagic particles to a depth of 5500 m based on surveys performed with a custom-made holographic microscope. The particle spectrum was unusual in that particles of several millimetres in length were almost 100 times more abundant than expected from the number spectrum of smaller particles, thereby meeting the definition of “dragon kings.” Marine snow particles overwhelmingly contributed to the total particle volume (95–98%). Approximately 1/3 of the particles in the dragon-king size domain contained large amounts of transparent exopolymers with little ballast, which likely either make them neutrally buoyant or cause them to sink slowly. Dragon-king particles thus provide large volumes of unique microenvironments that may help to explain discrepancies in deep-sea biogeochemical budgets.

Eukaryotic microbes, principally fungi and labyrinthulomycetes, dominate biomass on bathypelagic marine snow

“…The variability in taxonomic composition of eukaryotic microbes was high in that study with much of the variance explained by water mass (Pernice et al, 2016). As the amount of deep-sea marine snow changes dramatically by water mass and location (Bochdansky et al, , 2016, some of the high variability in microbial eukaryotes is very likely due to the relative abundance and type of marine snow in these layers.…”

“…However, these sediment traps collect fast-sinking particles with much higher efficiency than slowly-sinking particles, while buoyant particles are not collected at all. Recently, we demonstrated that bathypelagic particles in a size range from 400 μm to several mm were more abundant than expected from the number spectrum of smaller particles (Bochdansky et al, 2016). Approximately 30% of these particles did not contain apparent ballast, such as fecal pellets or dense phytodetritus, but a large amount of transparent exopolymer particles (TEP, Alldredge et al, 1993), which led us to conclude that they are either neutrally buoyant or slow sinking (Bochdansky et al, 2016).…”

“…However, the bathypelagic ocean is beyond the reach of divers, and submersibles are prohibitively expensive to deploy over large ocean regions as encompassed in this study. In addition, marine snow less than a few millimeters is very difficult to collect from a submersible (Silver and Alldredge, 1981;Alldredge and Youngbluth, 1985) so that a large portion of relevant particles (4400 μm) is unaccounted for (Bochdansky et al, 2016). Although we concede some inefficiency in our sampling protocol, we are also confident that marine snow was retained by our method.…”

“…The high TEP content of deepsea macroscopic particles, especially those in the range of 400 μm to several mm in size, could contribute to that buoyancy (Atsetsu-Scott and Passow, 2004;Bochdansky et al, 2016). Slowlysinking and neutrally buoyant particles would allow sufficient time for complex eukaryotic microbial communities to form on the high organic nutrients available in particle matrix and pore water.…”

“…Recently, we demonstrated that bathypelagic particles in a size range from 400 μm to several mm were more abundant than expected from the number spectrum of smaller particles (Bochdansky et al, 2016). Approximately 30% of these particles did not contain apparent ballast, such as fecal pellets or dense phytodetritus, but a large amount of transparent exopolymer particles (TEP, Alldredge et al, 1993), which led us to conclude that they are either neutrally buoyant or slow sinking (Bochdansky et al, 2016). Neutrally buoyant or slowly-sinking marine snow has previously been suspected to contribute significantly to the metabolism of the deep sea, providing hotspots of microbial diversity and activity Burd et al, 2010).…”