Deep Sea Minerals - Vol 2 - Manganese Nodules

2.3

Composition of sea-floor communities

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 Deep sea communities are generally divided into four body-size classes for study and description: megafauna, macrofauna, meiofauna, and microfauna (Figure 17).

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)

Size of life in the deep oceans

Megafauna

Macrofauna

Meiofauna

Microfauna

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

Figure 17 Faunal size classes routinely found on the abyssal plain.

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