I agree with you but at the same time there huge swats of the ocean that are the equivalent of aquatic deserts. Specially on the Atlantic. So much so that frequently structures are sinked in order to create better conditions for species that were overfished. But those zones of the ocean being barren is not related to human activity so much as they are just a bit too harsh and empty. So maybe if you could store the carbon there and at the same time create structures to improve conditions it would be net positive for biodiversity.