Box Jellyfish in Mauritius

I was on holiday in Grand Bay (North) Mauritius and on my last night on the island I planned a night swim. I got about knee-deep in the water and changed my mind for some reason. Later that night, we were walking along the beach and started seeing many small rectangular shaped jellyfish being washed up along the beach. One of the guys I was with, said that it was a boxjelly fish but I wasnt convinced as it just didnt make sence. I Googled them as soon as I got back to South Africa and and saw that they were indeed Box Jellyshish (an unusual place for them to be) and accuratly timed according to lunar predictions - about 12 days after the full moon?!