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a Adapted from Heywood and Whitaker (1984) and Picken (1985). b Phyla are identified or noted in parentheses. c Estimated from Arntz etal. (1997).

a Adapted from Heywood and Whitaker (1984) and Picken (1985). b Phyla are identified or noted in parentheses. c Estimated from Arntz etal. (1997).

whales in the Antarctic marine ecosystem range in size up to the blue whale (Ba-laenoptera musculus, Table 2.1), which has a maximum length exceeding 30 meters and is the largest animal ever to inhabit the Earth.

Diverse and abundant assemblages also inhabit the Antarctic marine benthos on (epifaunal) as well as in (infaunal) the sediments (Plate 10). Microbenthic species include various algae and bacteria forming dense mats. There also are protozoans, single-celled animals with unique feeding adaptations, such as the forami-nifera that glue sand grains together into filtering forms like small trees several centimeters high. Among the macrobenthic faunas, there are various molluscs, giant sea spiders, starfish that stretch 30 centimeters across, sea urchins, meter-long nemertean worms, crustaceans, and fish. At greater depths, which are more sheltered and less disturbed, there is an increase among the larger sedentary filterfeeding organisms, particularly the sea cucumbers, bryozoans, sponges, hydroids, soft corals, and tunicates.

In this adaptive interplay between species and their environments, fossil assemblages of extant species further reflect both environmental variability and biotic

T ABLE 9.1 Levels of Ecological Organization for Interpreting Interactions Between Species and Their Habitats

Ecological level

Ecological characteristics

Individual Population Community

Ecosystem

Biosphere

Energetics of an organism that are influenced by available resources, environmental variability, and its inherent adaptations (Figs. 9.8-9.10) Density, biomass, and size frequency of individuals from the same species interacting within a specific habitat (Figs. 9.3 and 9.5) Diversity and biomass of different species interacting within a defined type of habitat (Figs. 9.1, 9.2, 9.4, and 9.6) Flow of species' biomass and production among prey, predators and competitors from diverse communities across a range of habitats within a bounded region (Fig. 9.7) Life on Earth (Plate 1 and Fig. 9.11)

In addition, the complexity of life is reflected over time and space by the bio-geography of species (Figs. 1.6 and 6.1). For example, as Antarctica cooled and became thermally isolated during the Cenozoic (Chapter 6: Spreading Planet), organisms developed specialized adaptations and restricted distributions. With ocean temperatures that freeze freshwater, Antarctic fish became dominated by species in the suborder Nototheniodei that have a glycoprotein antifreeze (as in car radiators) to prevent their blood from becoming solid ice that would burst cells like filled water bottles in a freezer. Among the notothenioids, there also are ice-fish that certainly are evolutionary curiosities as the only vertebrates without red blood cells (hemoglobin) for carrying oxygen throughout their bodies. As a consequence of such adaptations, levels of endemism exceed 90% among the fish and other marine taxa living around Antarctica (Table 9.2).

Similarly, responding to the circumpolar circulation of the Southern Ocean, which has been operating since the late Oligocene (Fig. 6.5 and 8.3), marine species also evolved distributional patterns that ring the Antarctic continent (Fig. 9.1). Moreover, reflecting their evolution between deep-sea and coastal habitats— which are both cold, sheltered, and dark, with prolonged periods of low production—bottom-dwelling (benthic) species commonly have depth ranges exceeding 1000 meters across the Antarctic continental shelf.

In the open sea (pelagic) realm of the Antarctic marine ecosystem, there are micron-size viruses and bacteria along with various phytoplankton which are dominated by diatoms with more than 100 species among genera such as Thalas-siosira and Chaetoceros (Fig. 9.2). These species are consumed by various zooplankton, including fish larvae, ctenophores, salps, arrow worms, polychaetes, and pteropods, as well as diverse crustacea among the ostracods, copepods, mysids, euphausids, and amphipods, which can be several centimeters long. The largest of the Antarctic zooplankton are jellyfish, some with tentacles extending many meters (Plate 6). Still larger free-swimming (nektonic) fish, squid, seals, and

FIGURE 9.1 Generalized biogeographic zones (with tick marks at 10° latitude increments) based on the diversity of species in the Antarctic marine ecosystem (Fig. 9.2) that are strongly influenced by the circulation and historical development of the Southern Ocean (Figs. 6.5, 7.8, and 8.3). Modified from Hedgpeth (1969).

FIGURE 9.1 Generalized biogeographic zones (with tick marks at 10° latitude increments) based on the diversity of species in the Antarctic marine ecosystem (Fig. 9.2) that are strongly influenced by the circulation and historical development of the Southern Ocean (Figs. 6.5, 7.8, and 8.3). Modified from Hedgpeth (1969).

responses in the Earth system today (Plates 5 and 6). For example, guano deposits on emerged beaches reflect the population persistence of Adelie penguins in stable habitats along the Victoria Land Coast during the past 6000 years (Fig. 9.3). Similarly, living moss banks in the Antarctic Peninsula region and mats of primitive algae in permanently ice-covered lakes in the McMurdo Dry Valleys also have been thriving since the mid-Holocene—much like species in other habitats around the Earth (Chapter 7: Flowing Planet and Chapter 8: Breathing Planet).

With desert levels of precipitation (Fig. 8.7), Antarctic terrestrial species generally are restricted to ice-free coastal oases where there is a modicum of seasonal snowfall and melting. Algae have adaptations for dehydrating themselves as well as becoming insulated alive within sandstone rocks. There also are tiny mites, less than 3 millimeters in size with glycerol in their blood, nestling under rocks and in sand or other moistened habitats in temperatures below -30°C. Among these minute arthropods, which nonetheless are the largest animals on Antarctica, Na-norchestes antarcticus survives down to 85° south latitude as the southernmost terrestrial animal on Earth.

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