Drove through some type of seaweed, went to start engine,engine started fine once I gave it gas rpms jumped up and I really wasn't going any where. So I went to pull all the seaweed out of the grate,pulled it all out, I also switched fuel tanks before I started it up, gave it some gas it started going thought I fixed the problem then about 15 seconds later engine shut off. Dont know if its the pump causing the engine to shut off and there's still stuff in the pump ? or my fuel not getting to the engine? Can someone help me out thanks

Junk in the pump will not cause the engine to die unless it's really binding the pump. 

Junk in the pump will stop water flow to the engine causing an overheat.  A severe overheat will cause the engine to shut down but not in 15 seconds.

Good chance that the shut down is fuel related.