It tends to be easiest to tell the different mangrove species apart by looking at the shape of the propagule. Red mangrove has long cigar shaped propagules from 4-8" in length typically and black mangroves have small heart or bean shaped propagules that are 2-3" in diameter. These two are the most common ones.
I am really not sure that 75watts is going to be enough to get a mangrove to grow well. They are slow growers to start with and need pretty intense light to do well. Some of the best setups with them have used sunlight, such as
Triteriums' setup seen in this thread. He is also using red mangroves in these shots.
See also
Reproductive strategies of mangroves for pictures.
Edit: Well there you go, he beat me to the punch.
>Sarah