GEOPHYSICAL MONOGRAPH SERIES, VOL. 43, PP. 379-390, 1987
Seamount benthic ecology and potential environmental impact from Manganese crust mining in Hawaii
The benthic megafauna on Cross Seamount (18°40′N and 158°17′W) is characterized by patterns of low diversity and abundance.
Various factors that might account for this include geographic isolation, small habitat area and unfavorable environmental
conditions. The seamount is isolated both geographically and due to weak surrounding bottom currents. Small habitat area in
combination with isolation, may restrict colonization of the seamount to species that produce only long-lived larvae. The
progeny of such species, would in turn be expected to be swept away before settling, resulting in parent populations low in
abundance. Unfavorable environmental conditions including sluggish bottom currents may also reduce recruitment by failing
to maintain substrata free of sediment. Highest population densities were found concentrated on large rocky outcrops and summit
rim areas probably subjected to accelerated water flow. In zones characterized by thick ferromanganese crust deposits, patterns
of abundance were particularly low suggesting the possibility of larval avoidance of such areas. The dominant faunal elements
are gorgonian corals and solitary anemones. Two species of precious coral were discovered although neither in commercial abundance.
The low biotic diversity and abundance and commercial insignificance of the benthic megafauna on Cross Seamount suggests that
environmental impacts produced by manganese crust mining operations in this region of the Hawaiian EEZ would be minimal to
this portion of the biota. Further study is needed to better ascertain the abundances of bottom commercial fishes and crustacean
resources as well as pelagic species and the extent of potential impact to these organisms from crust mining.
Citation: Grigg, R. W.,