MANGANESE NODULES
23
Composition of sea-floor
communities
2.3
The biology associated with manganese nodules has been
studied most intensively in the CCZ. However, the environmen-
tal conditions and factors affecting faunal communities are like-
ly to be generally applicable to other abyssal plain habitats and,
hence, relevant for the southwestern Pacific.
Sea-floor communities in the CCZ exist in what is called the
mesotrophic abyss, a region of moderate particulate organ-
ic carbon flux and food availability by abyssal standards. The
sea-floor in this region is heavily modified by the activities of
animals. Xenophyophores (giant foraminifera ranging from 3 to
10 cm in width) are abundant, with furrows formed by burrowing
sea urchins and spoke-like feeding traces and faecal mounds
from spoon worms appearing occasionally (Smith and De-
mopoulos 2003). These sea-floor animal traces are remarkably
persistent, due to the physical stability of the sediment. In the
CCZ, animal tracks and trails ranging in size from millimetres to
centimetres last longer than 12 months before they are erased
by biological or physical processes (Gardner
et al
. 1984).
Megafauna are the largest animals in CCZ benthic (sea-bottom)
ecosystems. These are animals large enough to be recognized in
bottom photographs and range from about 2 cm to more than 100
cm in length. Megafauna include omnivorous fishes (especially
rattails), cephalopods (such as octopus and squid), scavenging
amphipods and deep sea shrimp, large deposit feeders such as
sea cucumbers and starfish, and suspension-feeding glass spong-
es, anemones, and other cnidarians. More than 20 megafaunal
species can occur in seemingly homogenous areas of 1-2 km2. Xe-
nophyophores are typically the most abundant megafauna in this
region (Smith
et al
. 1997; Smith and Demopoulos 2003).
Photographs of animal tracks and faecal mounds on the sea-floor
in the CCZ, taken with a time-lapse camera (Gardner et al. 1984)
Animals identi able from
bottom photographs and videos
Animals retained on a 0.3
to 0.5 millimetre sieve
Animals passing through a 0.3
millimetre sieve and retained on
0.032 to 0.063 millimetre sieves
Organisms passing through
a 0.32 millimetre sieve
Size of life in the deep oceans
Microfauna
Meiofauna
Macrofauna
Megafauna
Figure 17 Faunal size classes routinely found on the abyssal plain.
Deep sea communities are generally divided into four
body-size classes for study and description: megafauna,
macrofauna, meiofauna, and microfauna (Figure 17).
