In recent weeks, many bathers and tourists have noticed the large amount of sea mucilage present on the coasts of the central and northern Adriatic, particularly in the Gulf of Trieste but also in the Marche and Emilia-Romagna. This “explosion” of mucilage is due to the proliferation of microalgae (in particular Gonyaulax fragilis) that produce polysaccharides and proteins thanks to which mucilaginous aggregates are formed. Mucilages, however, tend to they do not constitute a health hazard.
Contrary to what one might think, in fact, the phenomenon of mucilage is completely natural and has nothing directly to do with marine pollution, even if their appearance makes it seem so.“dirty” water. It is essentially a gelatinous aggregate formed by proteins and polysaccharides produced by photosynthetic microorganisms (microalgae, cyanobacteria) or macroalgae, which contain remains of microorganisms, organic substances and various debris. Therefore, if microalgae increase, the mucilage phenomenon will tend to intensify.
In the case of the last few weeks in the Adriatic, the proliferation was caused by two main causes. The first is the high water temperatures: in the last month Italy has been hit by intense heat waves and also the Adriatic is a very shallow sea, so it tends to be particularly warm (a bit like a shallower swimming pool tends to be warmer than a deeper one). The other cause is the intense influx of fresh water in the Adriatic due to intense rainfall that alternates periods of heat and sultriness, for example with heat storms: more water falls than the ground can absorb, this water flows away and eventually ends up in the sea. An influx of fresh water temporarily reduces the salinity of the sea and, together with high temperatures, puts microalgae Gonyaulax fragilis and other microorganisms in a condition to proliferate.
In general, The Adriatic is very susceptible to the phenomenon of mucilage because it is particularly closed, small and shallow: for these reasons it heats up easily, receives a lot of fresh water from the Po and other rivers and has few currents, making the proliferation of phytoplankton more likely, which contributes to the formation of mucilage.
Although these days we often hear that mucilage “has returned” to the Adriatic, the truth is that they hadn’t disappeared before: simply the phenomenon proceeds to waves of intensity depending on the climatic and environmental conditions. In periods of low intensity, the mucilage does not necessarily disappear: it can also be found offshore, not visible from the coast. The phenomenon has been known and documented in the Adriatic at least since 1729but it has become particularly frequent since 80’swith “explosions” almost every year. Global warming does not help in this sense, increasing the surface temperatures of the seas and of the Mediterranean in particular.
