It’s important to realize that most of the life in the sea is microscopic. Some organisms including bacteria, microalgae, and viruses are only a few micrometers in size. (A micrometer is one-millionth of a meter.) You can imagine the survival challenges you would face as a single-celled organism living among hordes of microscopic predators and competitors.
One way these animals protect themselves is with mucus. However, sometimes some of the mucus is shed into the sea and floats around as nanometer-sized “microgels.” (One thousand nanometers make up a micrometer.) As cells die, they also release some large molecules able to form gels. There is nothing unusual about microgels in all areas of the sea, but, generally, they do not amass into a huge gel of slime.
In the northern Adriatic Sea, we really don’t know the complete story. We believe that part of the problem is pollution. There is a huge river that runs into the northern Adriatic, called the Po River, which carries large amounts of fertilizer ingredients like nitrogen and phosphorous, mainly leftover from agriculture upstream. Some unknown trigger that could be related to the pollution makes the microgels and molecules tangle up and coalesce into huge gels very quickly, within a few days.
We do not yet know the trigger. However, we are testing some hypotheses in the laboratory by creating blooms of algae in large bottles filled up with northern Adriatic seawater and fertilized with nitrogen and phosphorous. We are beginning to get a glimpse of what might cause the formation of huge and dense gels in the northern Adriatic Sea. The plot thickens.
-- Farooq Azam, distinguished professor, Marine Biology Research Division