ocean engineering

Staying ahead of commercial exploitation in the deep sea

Boschen, R.E.; Rowden, A.A.; Clark, M.R.; Barton, S.J.; Pallentin, A.; Gardner, J.P.A. Megabenthic assemblage structure on three New Zealand seamounts: implications for seafloor massive sulfide mining. Marine Ecology Progress Series 523: 1-14, 2015. doi: 10.3354/meps11239

Why we care

Seamounts are underwater mountaintops. They are enormously important topographical features that serve as biodiversity hotspots, providing unique biological oases in the ocean abyss. Humans have harvested fish from seamounts and their surrounds for some time, but in the future, seamounts may also be commercially mined.

This is a case in which commercial endeavors seem to be outpacing the advancement of science accompanying them. That is, seamounts are at risk from mining but we have relatively little information about what these seamounts are like on average. So it is difficult to suggest what limits should be placed on mining: how much extraction is too much? Is intensive mining on a few seamounts better or worse than light mining on many seamounts?

It has been suggested that a unique collection of organisms may live on seamounts along seafloor massive sulfide (SMS) sites due to the unique chemical environment there. Before this study, only one SMS area had been formally characterized. The authors of this paper performed broad-scale benthic profiling of SMS sites in New Zealand and related organismal trends with SMS mining potential. This is a first step in managing natural areas at risk from a new type of resource extraction.


Seamount locations northeast of New Zealand’s north island (shown in white). The purple areas have been licensed for SMS mining exploration (anticipated to begin in 2017), while the purple line in the inset denotes New Zealand’s exclusive economic zone.

Surveys were conducted on three seamounts: Rumble II East, Rumble II West, and Brothers. These seamounts are hydrothermally inactive with no SMS deposits, hydrothermally inactive with SMS deposits, and hydrothermally active with forming SMS deposits, respectively. All seamounts are within the depth range of 900 to 3025 meters and are relatively close to one another.

Video transect data were collected from these seamounts in 2010 and relative abundances were considered. Benthic faunal information was paired with a variety of environmental descriptors, such as slope and rugosity, gathered using a multibeam echo-sounder. For those interested in the details of their statistical analyses of these data, the authors provide extensive details of their multivariate analyses in the paper.



Topography of the three chimneys with transects superimposed on them as series of dots. Each dot type represents one of the 20 assemblages found across all three surveyed seamounts. Red stars show the locations of hydrothermal chimneys seen in the transects.

A total of 186 taxa were identified from the three seamounts. Both seamount identity and the habitat within each seamount significantly influenced faunal assemblages. Analyses indicated 20 statistically different assemblages on the three seamounts, only six of which were found on more than one seamount (4 of these were found on all three seamounts).

The most influential environmental variables in determining community structure both among and between seamounts were magnetivity, depth, substratum, and topography. Magnetivity can be a proxy for hydrothermal activity, while depth, substratum, and topography commonly influence sessile benthic oceanic community composition.

This study suggests that setting aside a number of seamounts for complete protection while allowing mining on others would not be a suitable conservation strategy in the long run. Seamount communities varied widely amount seamounts, meaning that this strategy may allow considerable assemblage loss. Instead, the authors suggest a network of “set-aside” sites composed of multiple habitats from multiple seamounts. Most mining damage is expected to be localized, so such a strategy might protect a higher biodiversity of benthic fauna. This study also suggests that inactive SMS areas may support unique species assemblages, indicating that science may play an important role in shaping protective environmental strategies as the first SMS mines are opened.

Have you ever encountered resource extraction in the environment (logging, coal mining, etc.)? What was it like? Were environmental impacts what you expected (Could you see them? Was the environment constantly or only intermittently affected? Did anything surprise you?)?

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