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Here’s a trick that can work. Once you get the concept, you can apply it in different ways.
All your underwater surfaces should have a specular surface on them - blinn, perhaps, with the eccentricity turned up fairly high to distribute the specular widely across the surface.
All your lights should have the “emit specular” set to off, except one - this can be a directional light or spot light or whatever - but turn the “emit diffuse” to off, so that it only emits a specular highlight.
Create two marble maps and a blendColors node; connect the two marble maps to color1 and color2 of the blendColors, then connect the output of the blendColors to the color of the specular light.
Adjust the attributes of the marble maps (i.e., vein color = light gray, filler color = dark gray, vein width, diffuse, etc,) and test render enough so you like the look of it. Rotate one of the placement nodes 60 or 90 degrees on Y so the marble striations go in different directions - stuff like that.
Finally, keyframe the placement nodes, or use zig-zag motion paths for them. When you render a sequence, the specular highlights will “dance” on your surfaces. Adjust the speed and shape of the motion paths to your liking, and perhaps set them to “oscillate” in the graph editor.
You can also use this marble map thing as a specular map on all your surfaces instead (or in addition). Since caustics actually multiply light, you can connect this blend colors node to the glow intensity of your shaders; you’ll probably have to use a clamp or a set range node to tone it down a little.
With some tweaking, this can look pretty good - but it’s also pretty easy to make it look cheesy.
Finally, you should output this as a specular layer only, so you can adjust it further in post.
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