1.13.2 upgrade question

My server has been around since the early days (1.7.4) and has weathered every update since, and will continue to do so...but now, for the first time, an update has left me feeling like the 20k x 20k + blocks of Blockendale has empty ugly oceans. I know there's probably not a way, and no real solution, but I have to ask...is there any way, any script, any command block, anything, that can fill an older area with what would otherwise be it's natural seascape (at least plants and maybe some coral). I expect the answer is no, but in areas where we've done things like drain a monument and turned it into an exhibit, it would be nice if the surrounding waters didn't feel so dead and empty...at need we will likely have to hand place coral and plants to keep these places from feeling so empty...but is there a better way?