View Full Version : Suprisingly low salinity

12-30-2012, 08:14 AM
I was out with Louisianna Fisheries recently doing catch assessments in the area directly south of New Orleans, and I was suprised at how low the salinity was for how many inverts they have out there.

I the area is to muddy for corals, but they do have oysters, sponges, TONS of comb jellies and of course shrimp and lots of other inverts. When we were out doing the assessments the salinity was mostly 5-12 parts per thousand with a couple areas in the 15-18 PPT range. What is really amazing is the area where all the oysters grow is often down to 3-4 PPT and stays there for weeks or even months at a time during spring and early summer. In fact, according to the fisheries guys, apparently it is not uncommon to see it as low as 1 PPT for a few days at a time.

Makes me curious about salinity in aquariums, especially for softy tanks that are more inshore and near shore species.

12-30-2012, 09:05 AM
Those are creatures that have evolved to live in brackish water. They clean the fresh water run off that goes into the ocean. Corals are not the same, there is no such thing as a brackish coral nor can they tolerate salinity outside their normal range (32-36ppt).


For aquarists who depend on hydrometers for measuring their aquarium water's salinity, adequate salinity for their organisms is represented by specific gravity values in the range of 1.025 to 1.026. In spite of this, some manufacturers still recommend mixing artificial sea water to a specific gravity of about 1.022. Such a value results in salinities between 28 and 30 ppt, well outside the range for long-term survival of most coral reef organisms.

Coral reef animals are, indeed, delicate and hard to keep alive. Anybody can prove this by getting some of these animals and keeping them at temperatures that are abnormally low, abnormally high, or under salinity conditions that stress the animals to their maximum limits. Under such conditions, is it any surprise that the animals die when the slightest other factor goes wrong? It should not be, and neither should the observation that many of these animals also will simply just die from prolonged exposure to those conditions.