Shinji Tsukawaki

Composition of aquatic invertebrates associated with macrophytes in Lake Tonle Sap, Cambodia

Faunal composition of aquatic invertebrate communities associated with submerged parts of several species of macrophytes were studied in different areas in littoral Lake Tonle Sap in Cambodia, with special reference to those in root systems (interrhizon) of a free-floating water hyacinth (Eichhornia crassipes). Nine phyla of invertebrates were collected, of which oligochaetes, shrimps and Limnoperna mussels were abundant along with meiobenthic crustaceans. The macrophyte-associated invertebrates in Lake Tonle Sap might be unique in having abundant sessile animals, such as sponges, bryozoans and Limnoperna mussels. The Limnoperna mussels attached to macrophytes were more abundant in offshore and inundated forest than in secluded vegetational stands toward the shoreline. It suggests that water movement can be an important factor determining the distribution and abundance of the sessile animals by controlling larval dispersions and might be associated with the hydrological characteristic of the lake, i.e., the lake opens to the large Mekong River with drastic seasonal changes in water level.

Water temperature, salinity ranges and ecological significance of the three families of Recent cold-water ostracods in and around the Japan Sea

Abstract Water temperature (T) and salinity (S) ranges for the modern distribution of relict species of cold-water ostracods in and around the Japan Sea are summarized. These results provide new information on the ecology of species in the Omma-Manganji ostracod fauna and their survival through Pleistocene environmental changes. Fourteen representative species of this fauna belonging to the three families Hemicytheridae, Cytheruridae and Eucytheridae are discussed. The summer T-S habitat requirements were divided into three species groups: (a) Japan open sea-inner bay (0–20°C, 30–341; 9 species); (b) Japan-Alaska open sea (around 5°C, 31–341; 1 species); (c) Japan open sea (0–20°C, around 341; 4 species). The winter T-S of these three species groups falls in a single range of 0–5°C and 30–341. Their summer T-S conditions are characterized by a wide range either for T or S or both. The summer T range of most species reflects the Tsushima Warm Current water in summer. The winter T range of all the species corresponds to the coldest Japan Sea Intermediate-Proper Water through the year. The large T range difference between summer and winter is a remarkable character of most species. It is clear that most of these species examined here also live in temperatures as high as 20°C, but are generally cold-water species as a whole. The winter low T (less than 5°C) is considered to be critical for the survival of all of these species. These species were interpreted as having survived the cyclic environmental changes between glacial and interglacial periods by expansion or contraction of their distribution. Group (a) species can inhabit various T-S environments in summer. Furthermore, they can probably breed and maintain their populations, even in small areas such as the restricted inner bay, when suitable open sea conditions were lost. Group (b) species have only recently migrated to the low T-S region in the Northeast Pacific, and low T regions of deeper areas of the eastern Japan Sea where only a few species live. Group (c) species invaded the newly appearing T-S condition in the shallow-open areas of the Japan Sea, and have flourished, replacing the extinct species during the Pleistocene. Their wide T-S tolerance is considered to be the most advantageous factor for survival through the Pleistocene environmental fluctuations in the Japan Sea, linked with the glacio-eustatic sea-level changes.

The Impact on Bottom Sediments and Ostracods in the Khlong Thom River Mouth Following the 2004 Indian Ocean Tsunami

Abstract. Fossil ostracods are a useful tool for identifying tsunamigenic sediments. However, the behavior of ostracod shells within the bottom tsunami sediments in Recent river mouths and estuaries is poorly understood. In this study, we analyzed bottom sediments and ostracod specimens taken from sites within the Khlong Thom River and sites adjacent to the Malacca Strait along the Malay Peninsula during three intervals—pre-tsunami, four months after the tsunami, and post-tsunami—to determine the impact of the 2004 Indian Ocean tsunami on the bottom sediments in the river mouths and estuaries. The broad distribution of the terrigenous plant material-bearing sediments in the Malacca Strait and the southern part of river mouth areas after the tsunami indicates that the sediments and the suspended materials deposited on bottoms were preserved for four months after the tsunami. However, no plant debris was recorded in the Malacca Strait, the southern part of the river mouth (RM), or junction areas between the river mouth and the estuary in 2008, suggesting that they had dispersed from the bottom during the three years and eight months after the tsunami. Of the bottom sediments taken four months after the tsunami, a few containing no plant debris were recorded in the northern and middle parts of RM, characterized by no ostracods or an abundance of adult and late juvenile instar specimens of Keijella reticulata. Based on these observations, we believe that small materials, such as plant debris and early juvenile instar ostracods, were transported from the bottom after the tsunami by the ordinary current. Previous investigations have captured changes in the abundance and density of meiofauna within a few days of a tsunami; therefore, the existence of some changes in ostracods that were able to recover during the four months may be considered, although there was no change in ostracod biofacies caused by the tsunami in the study area.

Influence of Large Seasonal Water Level Fluctuations and Human Impact on the Vegetation of Lake Tonle Sap, Cambodia

Lake Tonle Sap, the largest inland water body in Southeast Asia, encompasses unique ecosystems and wildlife adapted to large seasonal fluctuations in water level. The permanent waterlogged area of the lake is encircled by a vast floodplain, the inundated woodland being dominated by Barringtonia acutangula (Lecythidaceae), probably a major vegetation type of this ecotone, although human impact has degraded the floodplain vegetation and developed forest is restricted to a narrow band along the shore in the lowest water season. The aspects of seasonally inundated vegetation (i.e., variations in physiognomy, species composition, stratification, and distribution) on the coastal side of the floodplain (approximately 4 km in depth), located adjacent to the southern part of Siem Reap, was analyzed. Quantitative data for phytosociological evaluation were collected at 67 quadrats (10 m × 10 m each) during the low water seasons in 2005 and 2006, the sampling plots being classified by Two- Way Indicator Species Analysis (TWINSPAN) and ordinated by Detrended Correspondence Analysis (DCA). Two vegetation zones (i.e., extensive cropland and disturbed woodland), seven vegetation types (i.e., “Cultivated field,” “Fallow field,” “Shrub,” and “Tall-shrub” in the extensive cropland zone and “Scrub,” “Open forest,” and “Closed forest” in the disturbed woodland zone), and vigorous invasion and/or regeneration of Barringtonia acutangula over the study area were identified. Human impact (e.g., plowing, burning, and cutting for firewood) seemed to be inversely related to both duration of flooding and maximum water depth and to be the main cause of degradation of seasonally inundated vegetation.

Potential of High-Resolution Satellite Imagery for Mapping Distribution and Evaluating Ecological Characteristics of Tree Species at the Angkor Monument, Cambodia

Abstract Large trees play several vital roles in the Angkor monuments landscape. They protect biodiversity, enhance the tourism experience, and provide various ecosystem services to local residents. A clear understanding of forest composition and distribution of individual species, as well as timely monitoring of changes, is necessary for conservation of these trees. using traditional field work, obtaining this sort of data is time-consuming and labour-intensive. This research investigates classification of very high resolution remote sensing data as a tool for efficient analyses. QuickBird satellite imagery was used to clarify the tree species community in and around Preah Khan temple, to elucidate differences in ecological traits among the three dominant species (Dipterocarpus alatus, Lagerstroemia calyculata and Tetrameles nudiflora), and to identify crowns of the dominant species. Population structures of trees were determined using a 14.26ha study plot. Species name, DBH, height, height under the crown and crown area were recorded for all trees over 40 cm in DBH. Tree locations were also recorded so as to provide references for the imagery analysis. Ecological traits of the dominant species were estimated using regressions by an expanded allometric equation for both large and small trees, based on DBH, height, height under the crown and crown width. The total number of species in the study plot was 45. From a spatial perspective, the three dominant species over 100 cm in DBH were segregated from each other. D. alatus, L. calyculata and T. nudiflora were concentrated, respectively, along the approach to the temple, near the centre of the complex, and on the walls of the monument. Object Based Image Analysis (OBIA) conducted using QuickBird satellite imagery, showed that crowns of D. alatus were largely determined by maximum of NIR layer and mean of digital number in panchromatic layer. Differences in the parameters for both asymptotic height and spatial distribution among the dominant species, result from differences in ecological traits, and enhance the value of the tourism resource by providing a dramatic shift of forest scenery that can be enjoyed by visitors to the monument.