Dense bamboo coral attached to a large boulder of basalt provides ideal protection for smaller organisms. Click image for larger view.

Exploring the Interdependence of Geology and Biology on Seamounts

July 1, 2002

Michael Rowe, Graduate Student
Geosciences, Oregon State University

Seamounts exist in the oceans as isolated islands that support their own diverse ecology. Why do these seamounts concentrate a wide variety of biological life into a relatively discrete region? In part, this relationship appears to be driven by the geology of these undersea islands.

Murray Seamount, located in the Gulf of Alaska, provides an interesting glimpse of the relationship between geology and biology. With a rugged terrain of peaks, valleys, and ridges, Murray's rough topography is driven by basaltic lava flows, emanating from the summit and isolated domes on its flanks. The steeply dipping lava flows, evident on the flanks of Murray, are mostly barren of life, excluding the occasional anemone or sponge. The steeply dipping angle to the basalt flow and the relatively smooth surface creates a difficult substrate for organisms to attach to. It is also difficult for them to hide in this extremely exposed environment. Valley floors, covered with a thin veneer of loose sand and rounded pebbles, are equally desolate.

A steeply dipping lava flow, at roughly 1,000 m depth, is relatively barren of both sediment and biological life –part of the south flank of Murray seamount. Note the lone armored sea cucumber. Click image for larger view.

In contrast to the steep flanks and barren valleys, the ridges of Murray Seamount are teeming with life. Regions composed of large boulders and outcrops apparently can provide protection as well as stable growing surfaces, and are thus covered with various coral species, among other deep-sea organisms.

Crabs of varying sizes and species use both the coral and volcanic rock for cover, making this rugged terrain an ideal habitat. The constantly changing topography of Murray seamount therefore exemplifies this interdependence of geology and biology.

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