Re the seaweed: I agree that it makes the rocks look flatter. The green seems to cover any reflections? Perhaps you could use the fake stones layer to mask out some of the green on the rocks. Letting some of the rock show through should help to give it more dimension.
The small stones in the foreground have very regular spacing, almost as if they're placed on a grid.
As for a turtle trail... maybe an image map used as a displacement map.
http://tinyurl.com/4eecem should give you some ideas on shaping, although the beach loks a lot firmer in your scene so you wouldn't expect the tracks to be very deep
The reflectivity of the sand could be reduced gradually as it gets higher towards the dry sand, particularly in the distance where the slope increases but the refelectivity stays constant. This would add a bit more to the realism. Not sure about adding some water on the right... it would look good but a realistic water's edge on a beach opens up a whole new can of worms... maybe later
Still a great image
