Ecology of gel-like marine snow event in the northern Adriatic Sea

The development, aggregation, and senescence of amorphous marine snow aggregates in the northern Adriatic Sea off Rovinj, Croatia were investigated during an aggregation event from July to September, 1997. Aggregates and surrounding ambient water were sampled using SCUBA for bacterial and cyanobacterial abundance, dissolved oxygen, primary production, bacterial secondary production, dissolved organic carbon and dry weight measurements. Marine snow aggregates appear to be a rich protected environment that favors primary production and bacterial growth by making readily available marine organic moieties present in the gel's matrix. Aged aggregates form two separate zones: an outer well oxygenated almost transparent gel-like zone, and a dark almost-anoxic/anoxic central zone. The interstices of the aggregates contained high concentrations of dissolved organic carbon, especially in the central almost anoxic-anoxic zone, which can be correlated to microbial activity. When sinking below the pycnocline they efficiently bypass mid-water biota thus becoming an important component of the marine biological pump and a major mechanism for the movement of particulate and dissolved organic carbon towards the sea floor.