Unless you want to eat fish.
[0] In yesterday's NYT: https://www.nytimes.com/2019/01/10/climate/ocean-warming-cli...
"A new analysis, published Thursday in the journal Science, found that the oceans are heating up 40 percent faster on average than a United Nations panel estimated five years ago. The researchers also concluded that ocean temperatures have broken records for several straight years."
It's really disturbing.
There's a lot of fish (and other animals) in the top four meters, a lot of others in the forty meters below that, and somewhat less in the layer below that, but once you get to kilometers of depth things change. There are many species still, but fewer individuals of each species. Life also slows down — animals down there grow slowly and reproduce late.
I personally don't like to mine down there. We should make our mess where we can get to it, and can clean up any problems. But conflicts with fish aren't likely to be a big problem. Driving some rare species into extinction, perhaps releasing a bunch of contaminants where we can't clean up and don't know where they will flow, yes, both of those, but not conflicts with the rich fisheries near the surface.
"Bottom trawling also stirs up the sediment at the bottom of the sea. The resulting undersea plumes of “suspended solids” can drift with the current for tens of miles from the source of the trawling, introducing turbidity throughout the water that inhibits the transfer of light down to the depths where it is needed for photosynthesis in plankton, sea kelp and other undersea plants that serve as the basis for the marine food chain. Also, ocean sediments serve as natural safe resting places for many persistent organic pollutants (such as DDT and PCBs). Dredging these sediments up effectively reintroduces such toxins into the water where they are unwittingly absorbed and consumed by the fish we eat and other marine life already trying to cope with otherwise compromised undersea habitats. The sediment plumes also reintroduce nutrient solids from agricultural and other practices, increasing demand for oxygen in the water (causing algae blooms) and contributing to the outbreak of ocean “dead zones” devoid of marine life." [1]
[1] https://www.scientificamerican.com/article/saving-deep-ocean...
And of course there are comercial species of very expensive yummy crustaceans living there. A couple of trawls and all is lost for the next thousands of years.
What we do on the surface has far more effect on these species than does the researchers' mud-digging at far greater depths.
Actually even Lophelia should be considered in the category "too deep to worry about", because as you pointed out they don't photosynthesize. They don't interact with us, and they don't interact with anything we interact with.
First of all, you are forgetting that all corals are pelagic species.
The "too deep to worry about" and "don't interact with anything we interact with" is also wrong both as concept and also as fact.
Lophelia reefs are the coral reefs of temperate areas. Can be found between 30 and 3000 m deep.
Until relatively recent times, we didn't even knew that we have coral reefs in UK, Norway or Canada. Still we don't know a lot about this places, but coral reefs are among the most rich ecosystems in the planet supporting an astonishing amount of biodiversity. As any other reef we know that they provide refuge for a (still poorly know, but probably very high) number of crustaceans, other invertebrates and fishes. It seems that Is an important refuge for sharks for example. Sharks play a role in keeping healthy marine ecosystems.
Next Cape Cañaveral growths a similar (much shallower) cold reef in a relatively narrow band that was the first marine area closed for research in USA. The Oculina Bank area of particular concern. Many fisheries depend on the Oculina reef. Their damage was directly linked with the demise of Florida's grouper fisheries for example.
We are also also slowly understanding how complex are soft bottom ecosystems. Much more complex that we previously though. Under the silt there are the equivalent of fields of grasses and shrubs but carved on negative space.
Is not just sand, is also 4000 years old antipatharians, is really smart predators that hold the key to made robots coated in one of the most resistent bio-matherials known in the planet. One that is able to stand high pressures, but that is also light, and that can also generate ultra-fast movements enduring well the mechanical damage
In silt bottoms we can found animals able to literally make the water boil around them. They can raise the temperature of a tiny amount of water to around 4000 degrees C. And they can do it in less than a second. Not, I'm not joking.
And there is also the "too deep to worry about" and "don't interact with us" small Aequorea, that blew our minds and changed forever how we, humans, do modern biosanitary research in the entire planet.
Lots and lots and lots of valuable things for humans.