Salnity fluctuations stimulates snails breeding attempts

I would like to share with you my recent observation...
And ask a question later to who might know the answer :-)

I have a very small, 10g "experimental" tank with one bag
of Southdown sand on the bottom (yes, it is deeeep)...
Inside I have a lot of snails, macroalgae and some rock.

Since the main purpose of this tank is to observe the sand
dwellers like spaghetti and other worms, snails and nothing
super-delicate I do not have any automatic top-off system...
Unfortunately it happens often I neglect my manual top of
routine and I see sometimes evaporation like 1" which makes
big salnity fluctuations in a small tank like this one...

Everytime it happens I see strings of snail eggs on glass,
plants, rocks... everywhere. I have three kinds of snails
and all of them seems to react to salnity increase with eggs.
Some of them ("dark cerith" - Cerithium atratum) glue long
white strings of eggs sacs, others (unidentified black ones)
glue single sacs with eggs in random places of the tank...

The reason I link snail eggs with salnity is that one time
I have observed same snails laying eggs and it was also
the time I went for a week leaving the tank with no top off.

Why would be increased salnity the stimulus for snails??
What do they "think" happens... why are they tempted to
lay eggs, and does it happen in nature? I was thinking
the salnity of the ocean is pretty constant all the time...