The last time we "saw" mantas was in western Australia and it was a crazy system involving a dozen or more tourist boats and a spotter plane. Once the plane spotted a manta all the boats would converge on it and try to dump you in the water (snorkelling) ahead of it. Of course the poor manta would get the hell out of there as fast as it could. At best you caught a vague glimpse of it disappearing in the distance. It left a bad taste in our mouth!
Thankfully this time was different. We went down to the bottom where there are several big coral head "cleaning stations" where the mantas come to have the small fish clean their skin. It benefits both sides since the small fish get to eat the parasites etc. (Note: the mantas were not being fed by the divers, they came here naturally.) The dive companies had made a line of dead coral and rocks that we were stayed behind so we didn't disturb the mantas.
At first there was just one manta hanging around the cleaning station. The visibility wasn't great but it was still awesome to sit and watch. There was also quite a lot of current so it was a little tricky to find somewhere to hang onto the bottom while we watched, especially when trying to take photographs!
Soon a second manta arrived. The first one was white - a reef manta, this one was black - a larger giant oceanic manta. The reef mantas hang around one area, whereas the oceanic mantas travel long distances across the ocean. The reef mantas are slightly smaller, they only get to 6m (20ft) across versus the oceanic which can reach 9m (30ft)! These weren't quite that big but they were still impressive.
It was really cool when the mantas would leave the feeding station and cruise over towards us to check us out. Then we got a much closer look as they went right overhead. Amazing to have such a big animal swimming around you.
Even better, after a while, a whole group of mantas arrived. They danced and swirled above us so gracefully, like a ballet. Afterwards our guide said he thought they were mating.
We spent about 45 minutes sitting underwater watching them. It was fantastic.