Why does the male seahorse give birth

I'm doing a school project and I'm studying seahorses. I have to set in-depth questions, like why does the male seahorse give birth, and I've searched everywhere, but I can't find the answer.

The male seahorse gives birth. The male has the incubation pouch. The female delivers the eggs to that area, then the male fertlizes them. A short time later, the male enters labor and squirts the little seahorses out of the pouch.

Now in the seahorse world, things are a little different鈥?.well so we thought. Since it is the male that becomes pregnant and gives birth to the live baby seahorses, it would seem logical that the female seahorses compete amongst themselves for male partners to care for their eggs. Well, that is what we thought. However, research has shown that it is STILL the males that compete for females. When male seahorses want to impress a female, they have tail pulling competitions, dragging each other around on the bottom of the seabed. They also snap at each other with their snouts and wrestle with each other using their long curved necks. They also display their pouches to the prospective female by opening and closing them, filling their pouches with water and expelling it with force, to show the fitness of the pouch for the birth process.

So, in a nutshell. Male seahorses compete with each other to become pregnant for three weeks (during which time they cannot move around to search for the best food), go through 72 hours of labour and exhausting final contractions to release up to 200 baby seahorses. During this process the natural colour of the male seahorse drains from his body and he becomes white and pasty looking. The experience (yes, we have it on film) looks painful and I cannot imagine that he would want to experience a baby seahorse birth again. But, after a very short time, sometimes only hours, the male starts showing off his pouch, begging to be pregnant again.