cool... I like it when all the fifth years students start talking about their graduation thesis... so you said you were unable to find related case studies? invent ones... you don't have necessarily to find the exact naming "eco-hotel and a marine conservation center"  you can search... hotel designs, conservation centers , sustainable design, eco-systems, marine life, and maybe some other types of structures or infrastructures built in relation with the sea life.... all of what I know is that you're not even trying! I'm a 5th year student too :p... may I ask what school you go to?

jesus, what's up with the influx of lazy thesis students?

this isn't a thesis it's a studio project; a thesis is an investigation of a question/idea

Hey, i am 5th year student and for my thesis i am willing to design a aquamarine core which would include various different spaces.

I am not able to find the best relative casestudy, it would be the great help if i can get the reference.

If you are looking for precedent for marine science centers look into the Oregon Institute of Marine Biology, the Charleston Marine Life Center, the Hatfield Marine Science Center, and the Newport Aquarium (they do a lot of conservation type work.) You shouldn't have any problem finding hotel precedent. I took Oceanography and Marine Biology in high school and we toured all of these places. For OIMB and HMSC I'm certain you can call and talk to a MB student about their research and conservation efforts.