Maarten D. de Jong
In our first game, I taught (mistakenly I realized) that you have to own the coral before you can start attacking other corals. Now that I re-read the rule, it states that you can use opponents coral reef to attack others.. or even your own. Now I'm wondering does this mean that you can use unclaimed coral reef to attack others?
Yes, that's exactly what it means. Have you tried reading my Beginner's Guide alongside the rules?
And also does this mean that you can virtually start your new coral reef close to the oppenents and on your action 2 lay four tiles.. two of which would consume your opponents?
Yes, provided your tiles are stronger as indicated by the coral strength tiles, and the weaker coral's polyp tiles are not within the range of influence of any shrimp.
Or there has to be 2 tiles on the board already before you can add yours to consume other tiles?
No. As soon as a coral is 2 tiles big, it can grow over any other weaker coral (provided once again that there isn't any shrimp guarding the tiles you want to consume).
I'm sorry if the wording is confusing. I'm basically asking if you can start your coral reef from scratch and on the same action eat other coral reef.
Yes, you can; it is an integral part of the action 'Grow Corals'.
Another quick question, what is the fifth spot for the shrims on the open sea board for? Is there an expansion for 5th player I don't know about?
It's for the expansion Reef Encounters of the 2nd Kind, which was released at Spiel 2006 in Essen. You still can't play with 5, though.