The devices that scrape the ocean floor don’t appear to be the type of machinery that permanently alters ecosystems. They are unglamorous: mechanical rakes slicing thru material that hasn’t been disturbed in geological time, hefty dredge heads dragging behind ships, and suction pipes drawing sediment up from the bottom. What they’re doing is imperceptible from the surface. It’s total from below.
Every year, between 4 and 8 billion tons of marine sediment are extracted worldwide. This figure includes a variety of activities, such as the deeper seabed mining operations that have garnered the most recent regulatory attention, offshore sand extraction for beach replenishment, channel maintenance in ports and harbors, and coastal aggregate dredging for construction. It’s hard to keep the number in proportion to whatever you know. It is, by virtually all measures, one of the biggest physical interventions that humans undertake in any one type of ecosystem, and it takes place mainly without the kind of public awareness that would result from similarly scaled actions on land.
The aspect of this that most obviously distinguishes seabed dredging from other extractive industries is the biology of what is lost. A cleared region in a forest is at least made up of species that science has identified, researched, and, in many cases, is able to determine the population status of. The scenario is nearly the opposite on the ocean floor, especially in the deeper zones that commercial interests are increasingly focusing on. Over 90% of deep-ocean life is thot to have never been formally described by scientists. There is no database entry, no population estimate, no protected status, and no advocate for a species that inhabits the sediment layer of an abyssal plain. It disappears as soon as the dredging goes thru. No one is aware of its existence. No one will be aware of its disappearance.
The direct damage figures that do exist, such as a 30 percent decrease in local species counts and a 40 percent elimination of macrofauna along the direct disturbance path, originate from the shallower, better-studied benthic zones where before-and-after studies have been possible. Even by itself, such figures are noteworthy. However, the harm is being measured in areas where the wildlife was recognized to some extent. The same machinery is working against an unestablished baseline in deeper, less-surveyed zones. The loss is happening more quickly than the science required to quantify it.
Each dredging operation’s impact goes well beyond its actual track due to the silt plume issue. A cloud of small particles is suspended when heavy machinery passes thru bottom sediment. This cloud travels with ambient currents, often over long distances, before resettling. This resettlement covers areas that weren’t directly impacted by the machinery; it disrupts the microbial communities that control chemical cycling in the sediment column, covers filter-feeding organisms that need clear water to survive, and occasionally transports pollutants from disturbed anaerobic layers into the water column where they weren’t previously.
With the growing understanding of the connection between ocean sediment and climate control, the carbon dimension is being given more significant consideration. Organic carbon found in ancient seafloor sediments has been preserved across geological eras; it is not cycling or affecting atmospheric chemistry. When those layers are mechanically disturbed, the carbon is once again exposed to microbial breakdown and eventual emission as carbon dioxide. The effect’s direction is clear, but the amount of that release in relation to overall atmospheric carbon budgets is still being measured. The ocean’s ability to absorb carbon is weakened when old carbon-rich sediment is disturbed. No extraction permit mentions that expense.
A growing coalition of nations and conservation organizations is putting constant pressure on the International Seabed Authority, which oversees licensing for deep-sea resource extraction in international waters, to impose a significant precautionary pause on commercial seabed mining while the environmental assessment framework catches up with the science. That delay has been formally requested by dozens of nations. In anticipation of stricter regulation, a number of significant financial institutions and technological corporations have pledged to remove deep-sea minerals from their supply chains. It will be interesting to see if those pledges hold up when the struggle for vital minerals heats up.
