Big, empty scenes are always hard to do much with - you have to work for your compositions under these circumstances! (Unlike some other places where interesting shapes keep jumping out at you and you just have to decide which one of them you like best.)
The first thing one wants to do with them is back off or zoom out to try to capture the immensity of the scene. That rarely works - what it does it minimise the size of the small points of visual interest you have to work with and make them insignificant. You can (sometimes) just go stupid on the "I need to shoot this really wide to capture the sense of space" theory, and (sometimes) that works, typically somewhere close to the 10mm end of a 10-22; but it certainly doesn't work all of the time.
Then you can go hunting for some visual detail to start making a
composition with rather than just a snapshot. You've done that already with the gulls, the lighthouse, and the bit of seaweed (or whatever it is) at lower left. But, at least to my mind, those points of visual interest are too small, they don't do enough to the eye to make the picture work as a composition.
The third thing you can try - and it's surprising how often it works - is to go in the
opposite direction. Stop trying to imply enough detail in that vast scene to make a picture, shoot the detail and
imply the vastness. My favourite tool for this, by far, is the EF-S 60mm macro, very often in portrait rather than landscape mode. But I've done similar things with the 18-55 towards the longer end, with the 24-105, and (more often than I'd have imagined likely) with the short end of the 100-400. Hell, I have even used the 500/4 for landscape shots once or twice! But that 50ish to 100ish focal length range (100 to 150ish on 35mm) is what works most often.
Still, we have the shot that we have, and it's too late to swap lenses now. Where do we go from here? I would do something like this with it:
I've had to give up the larger bit of seaweed, but can make do with the smaller one to anchor the composition's lower left corner (often the most important pat of a picture). The eye is drawn from its natural starting place at lower left up and right along a series of details in the sand, then drawn back up and left along the white line of the ripples, and strongly back right by the breaking waves, picking up the lighthouse along the way. The seagulls reinforce the consistent lower-left to upper-right motion of the composition because that is the direction they are heading too - the eye follows moving objects and tries to anticipate where they are going to - and also, at a more subtle level, the seagulls symbolise movement, which is (as we have seen already) the theme of the picture. It is the seagulls more than anything else which do the work I spoke of earlier - it's their strong sense of movement out of the frame which creates that necessary
implied space of the rest of the coastline.
And the lighthouse, it too serves a function: being placed right in the centre of the picture (usually a very bad place to put stuff) it continually draws the eye back inside the frame. Without the lighthouse, the eye would just be pushed up out of the picture by all those strong diagonals.
All in all, we have taken a pretty scene and done something with it that works. I dont think it works brilliantly by any means, but it sort of works. But what it
really wants is to be taken from a few metres to the left of that spot, allowing the seaweed to be pushed in a bit, in turn allowing a more conventionally-shaped frame, and (more important) moving the lighthouse over towards the left-hand side more.
Your original as-shot composition is actually better balanced than that slightly weird thing I've concocted, but it suffers from : (a) a big hole in the middle where there is nothing of visual interest, and (b) that very strong horizontal line of beach and surf leading the eye out to either side where, again, there is nothing of visual interest.
There you go: just for you Dave, a genuine hand-crafted 80/20-mix critique.
(That's 80% BS, 20% nonsense - the usual mixture for these things, just ask a wine critic if you don't believe me.)
PS: I should have taken a tiny bit more off the right-hand side. No matter, close enough.