Shingo Ishikawa

A light trap to collect krill and other micronektonic and planktonic animals under the Antarctic coastal fast ice

SummaryUnder the Antarctic coastal fast ice a light trap proved to be promising device for collecting not only planktonic animals, but also micronektonic animals like krill which have been rarely collected with tow nets. Sampling was conducted at night from May through November, 1984 in Kitano-ura Cove off the East Ongul Island in Lützow-Holm Bay. Design of the gear and the sampling procedure are described. A total of 37 samplings were made that resulted in the collection of seven species of copepods, eight species of amphipods, three forms of notothenid fish larvae, two species each of euphausiids and polychaetes, and one species each of mysid, cumacean, isopod and tanaid crustaceans. All were collected in satisfactory condition for laboratory experiments. During the winter Euphasia superba was found to be benthopelagic and it probably feeds on detritus on the sea floor at about 40 m depth under the ice.

Seasonal Variation of Particulate Organic Matter Under the Antarctic Fast Ice and its Importance to Benthic Life

Qualitative and quantitative analyses were carried out on organic matter in suspended particulate matter of seawater for a period of 1 year under the Antarctic fast ice near Syowa Station in Luzow-Holm Bay during 1984/85. Marked seasonal variation of suspended organic matter, in particular chlorophyll a was observed. The concentration of suspended organic matter was generally high in summer and low in winter. The maximum value of chlorophyll a standing stock through the water column was 25 mgm−2 and the minimum was 0.4 mgm−2. Maximum standing stock of particulate organic carbon was 9076 mgm−2 and the minimum was 1632 mgm −2. However, the magnitude of the variation was low compared with the downward flux of particulate organic matter already reported for the same station. Suspended particles were rich in fresh algae and nutrients only during summer due to proliferation of phytoplankton and ice algae. Results of the present investigation suggest that feacal pellets produced by zooplankton and ice algal flocs detached from the bottom of fast ice in summer are responsible for the energy supply to benthic life under ice.

Mosaic structure of riparian forests on the riverbed and floodplain of a braided river: A case study in the Kamikouchi Valley of the Azusa River

Ecological studies of riparian forests in mountain regions in Japan have mostly been conducted in upper reaches where floodplains are relatively narrow with incised meandering channels (for example, Kikuchi 1968; Aruga et al. 1996; Nakamura et al. 1997). These reaches are subject to frequent disturbances of various type and magnitude and large floods can sometimes entirely remove vegetation from a reach (Sakio 1997).