Please interrupt any emerging notion of staying out of the ocean forever more and considering Nature’s grand disinfectant is at work to bring some stability to the ocean ecosystem. The world’s oceans are home to trillion - trillion microorganisms. This science is so new the microbes have not been named yet. The vast majority of the ocean microbes play roles in the life systems of the sea. Nature has a way to manage the burgeoning bacterial populations for reasons scientists have just begun to imagine.
Obviously human and environmental microbes are part of that flow. Just as essential is the nutrients; nitrogen and phosphorus get transported in the waters. (See the previous blog on Nitrogen) It is here that these nutrients and the microbes in water come to play out in a human-made change that compromises recreation water safety.
The bacteria in the water that might cause infection, like Staph. aureus is present almost always, yet their numbers are modest (Goodwin 2012). They are low from dilution, settling and the UV B of the sun. Problematically, this microbe is more common within the shoreline sand. Within the sand, it is fully shaded from the death ray UV B.
In the photo, the discs are all at the same depth, but the visibility is very different. The discs are readily homemade and equivalent to the commercial discs (http://www.instructables.com/id/How-to-Use-a-Secchi-Disk-to-Measure-Turbidity-in-a/).
In the figure to the right UV kill off of E. coli decreases significantly as the decrease of light transmission or penetration also decreases (Deller 2006). At 86% UV transmittance and 30 minutes exposure, almost 100% of the E. coli perish.
While this is illustrative and shows the importance of UV B penetration in seawater, it is not bacteria that cause most of the GI symptoms in ocean users. Rather, human enteric viruses are the most common cause of GI disease in general and in ocean recreationists as well. In Hawaiian waters in the dry season, swimmers risk of GI disease was most significant in waters with enteric virus present (Viau 2011).
The data indicate that the viruses are indeed more resistant to the ambient UV B and take about 8 to 9 days to reach levels associated with lower risk. The UV resistant adenoviruses remain above100 virus particles per 100 ml of seawater at 14 days.