The world can be a dark and cold place, maybe even a little rock-like at times. So the imagery of a fish wading through black stones adds to the struggle we all face while trying to get along in the world.
[…] illuminating the turquoise sea of bodies. (15-18)
The ambiguity of the word "bodies" here suggests that these sea creatures may represent something bigger than themselves. Maybe they are human bodies, either dead or alive, that allude to wartime and its consequences.
All external marks of abuse are present on this defiant edifice- (26-29)
The natural world—in this case the cliff—has "marks of abuse" just like people do. Some you can see but others may be internal instead of "external." But here the external marks are obvious, even though the cliff is "defiant" and will endure the abuse.