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The southern sea garfish Hyporhamphus melanochir fed on the seagrass Heterozostera tasmanica for 13 h during daylight, ingesting an estimated 3 gut volumes of plant matter, equivalent to 500 kJ d-I kg-' dry wt. No cellulase was detected in garfish digestive tissues, and gut pH was near neutral, but the pharyngeal mill efficiently triturated the seagrass tissue. Seagrass frond was assimilated at an efficiency of 38 % (organic matter). 28 % (energy). 50 % (protein) and 76 % (lipids), these being equivalent to the total components available in seagrass cell contents. Nocturnally emergent crustaceans were preyed upon by garfish over a period of 6 h and were processed at half the rate of seagrass. The daily energy intake, and probably assimilation, from this source was 223 W kg-' dry wt. Although the crustaceans consumed were only a third the quantity of seagrass, it was reasoned to be an essential source of protein, and at least as important as seagrass in satisfying the energy requirements of H. melanochir. Part TV in the series 'Study of Food Chains in Seagrass Communities' gut is used to estimate the ingestion rates for each of ' ' Present address: Biologische Anstalt Helgoland, Notke-these food types. We discuss the relative importance of straDe 31, D-2000 Hamburg 52 seagrass and animal food to the nutrition of this fish.

The prokaryote community activity and structural characteristics within marine sediment sampled across a continental shelf area located off eastern Antarctica (66°S, 143°E; depth range, 709 to 964 m) were studied. Correlations were found between microbial biomass and aminopeptidase and chitinase rates, which were used as proxies for microbial activity. Biomass and activity were maximal within the 0-to 3-cm depth range and declined rapidly with sediment depths below 5 cm. Most-probable-number counting using a dilute carbohydrate-containing medium recovered 1.7 to 3.8% of the sediment total bacterial count, with mostly facultatively anaerobic psychrophiles cultured. The median optimal growth temperature for the sediment isolates was 15°C. Many of the isolates identified belonged to genera characteristic of deep-sea habitats, although most appear to be novel species. Phospholipid fatty acid (PLFA) and isoprenoid glycerol dialkyl glycerol tetraether analyses indicated that the samples contained lipid components typical of marine sediments, with profiles varying little between samples at the same depth; however, significant differences in PLFA profiles were found between depths of 0 to 1 cm and 13 to 15 cm, reflecting the presence of a different microbial community. Denaturing gradient gel electrophoresis (DGGE) analysis of amplified bacterial 16S rRNA genes revealed that between samples and across sediment core depths of 1 to 4 cm, the community structure appeared homogenous; however, principal-component analysis of DGGE patterns revealed that at greater sediment depths, successional shifts in community structure were evident. Sequencing of DGGE bands and rRNA probe hybridization analysis revealed that the major community members belonged to delta proteobacteria, putative sulfide oxidizers of the gamma proteobacteria, Flavobacteria, Planctomycetales, and Archaea. rRNA hybridization analyses also indicated that these groups were present at similar levels in the top layer across the shelf region.The Mertz Glacier Polynya (MGP), located off eastern Antarctica, is a major latent heat polynya in which high-salinity shelf water is formed by brine rejection during ice formation. The high-salinity shelf water exits the shelf zone through a trough to the deep sea, where it contributes about 1.5 ϫ 10 6 m 3 s Ϫ1 of Antarctic bottom water (5), which is about 20 to 25% of total production. Antarctic bottom water has a major influence on ocean circulation and global climate and potentially on marine biota in the mesopelagic and deep oceans. Evidence from the Ross Sea Polynya suggests that surface production tends to be rapidly exported into deep waters and sediment (16). The presence of turbidity (detected by photography [13]) indicated that sediment transport and deposition was active above MGP shelf sediments and accumulates to form the Mertz Drift (24). Seabed photography revealed the presence of extensive benthic faunal populations, including arthropods, sponges, crinoids, asteroids, urchins, and anemone (13). Benthic communi...