帰国子女コミュのResearch on marine stuffs in PhD or master in Japan (Okinawa?)

Hi, I'm a universiy student in Australia studying marine biolgoy and finishing my degree in 1 and a half years. I was going to stay in Australia for a rest of my life but am obliged to go home to Japan after my degree for some reason. Yes, I'm Japanese.

So, does anyone know any unversity in Japan where they teach or communicate in English? I learned pretty much everything in English. So it would be easier for me to learn things in English now. I am thinking of doing PhD or master in Japan.

OR could you let me know if you know any Japanese universities which have Marine Biology (or ecology or whatever related to that sort) course where I can do PhD or master?

OR maybe I don't need to go to a university if I can pursue marine biology in some institutes or research stations. Please let me know if you can give me any suggestions.

Thanks a lot.