Life on the Jetty

This past weekend, I had a chance to spend a little time down at the beach.  I walked down to the end of the jetty, sat on a rock and took a look around.  This was the most active jetty I have been on, a large family had come down to try their hand at catching fish. While the small children ran around screaming and playing, dad cast a line into the water.  He calls down to a friend that is fishing from an innertube in the water to see if he's caught something...he has! After quite some time, the man in the tube reels in a small shark. Everyone on land is excited to see his catch, so the man paddles his way over to the family to show off his trophy. I presume that the catch is going to become dinner for the evening.
Below is a list of both living and non-living things that I observed as I sat:

Biotic:
People - approx. 15
dogs - 2
Seagulls/birds - approx 20
fish - approx. 6 which have been caught
ants - a few
kelp - a bunch

Abiotic:
Sand
rocks
water
wind
Sailboats
airplane
sea shells

There are quite a few relationships to be observed over time at the beach.  The fish which swim in the water, hide in the kelp and possibly eat it. The people that catch the fish to eat them. The birds which glide on the wind, swooping down to catch the fish, or pick the shellfish from the water to break them  open on the rocks, leaving the shells behind.