[dirtyroboto]

Quick and easy, Go Odiaba where you will see much marine life if you have the time and an eye for these things. Most people will just walk past natures show in ignorance and say "Odaiba, are you mad" but it is a good place to get close to marine while being a short journey.

I like Enoshima and Chigasaki. It is about 45 - 1.15 mins from gereral Tokyo and offers a diverse costal playground. You will see about 2.5 million people on surfboards in about 1km strech of water, quite a sight. But it also has many types of sea and costal beast to marvel at.