Re: How is siphoning, used in France, better than regular tide power?

You ask several good questions here.
1.  Sea life endangered by tidal power?  Almost always, sea life living in 
tidal areas has adapted to the covering/uncovering by water due to tides.  
In fact, many species need the exposure to air to survive.
2.  Locks are indeed expensive to build, although necessary for ships to 
travel up rivers.  The problem here is that fish have difficulty with locks 
and, more important, the locks destroy some marine habitats.
3.  Siphons are much easier on the bottom-growing marine species than locks 
due to the fact that you don't have to dig up a lot of ground to install 
one.  The problems are that you can't use the canal for ships and fish have 
trouble going up the siphons to spawn.

So each system has its good and bad points;  you have to consider all the 
tradeoffs before making a decision.