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Sediment Quality Assessment and Management: Insight and Progress Edited by M. Munawar© 2003 Ecovision World Monograph Series Aquatic Ecosystem Health & Management Society Influence of sea cucumber on sediment improvement in a closed aquatic environment K. Kurata1*, Y. Kozuki1, M. Kitano1, K. Otsuka2, H. Murakami1 1Ecosystem Engineering, Graduate School of Engineering, The University of Tokushima, 2-1 Minamijosanjimacho, Tokushima 770-8506, Japan. * 2Marine System Engineering, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuencho, Sakai 599-8531, Japan. Keywords: feeding behaviour, Stichopus japonicus, assimilation, acid volatile sulphide Introduction Coastal zones where the land meets the sea are often influenced by the various economic activities from the land. Especially in closed sea area such as inner bay or harbour, load of organic matter and nutrient from the river affects directly water and bottom materials in respect of physical and chemical qualities. Environmental deterioration of water and bottom qualities did damage to many organisms inhabiting closed sea areas. For example, lack of dissolved oxygen in bottom water and the emergence of red tide had a serious impact on marine organisms. The loss of balance of nature was likely to alter the function of ecosystems. Several methods for restoration of environment in closed sea area were carried out in the past: i.e., drainage system reducing the outflow of nitrate and phosphate, or the catalytic oxidation method between rocks decomposing organic matter in sea water. Reduction of outflow is essential for solving the problem, but only a water purification method like catalytic oxidation between rocks may be ineffective in broad coastal area. In addition, suspended solids deposited in the interspace between gravels are unlikely to be removed as sedimentation will continue in the future. In general, there are large amount of sediment derived from suspended solids in closed sea area, which drives elution of nutrient and lack of oxygen in bottom 242 water. It is important to consider effects of bottom material on water qualities for restoring the marine environment. Moreover, effective methods available in longer period is needed to recover the capacity for purification in nature. Because epiand infaunal benthic animals play an important role in sediment reworking, it is possible to utilize the function of these organisms to improve the bottom quality in sea areas where a large amount of suspended solids settled. In recent years, several researchers have studied on methods for sediment improvement, which applies feeding behaviour of deposit- and suspension-feeding animals. Kurihara (1980) suggested the utilization of polychaete Neanthes japonica inhabiting artificial mud flats for the part of sewage processing system. Montani and Tsutsumi (1998) studied a polychaete Capitella sp. and demonstrated the effect of sediment improvement caused by sediment feeding behaviour of this worm. Murakami et al. (1998) conducted field experiments for purification methods, which combined a polychaete N. japonica and the catalytic oxidation between gravels, reporting that the number of polychaete individuals was not retained due to predation in the field. Since these studies on sediment improvement methods utilizing function of macro-organisms have begun several years ago, quantitative assessment for the effect and extent of these methods in the field should be considered. It is said that common sea cucumbers, Stichopus japonicus, inhabit coastal area around Japan. In this paper, we investigated the effect of sediment improvement in closed sea area, which applies feeding behaviour of a common sea cucumber S. japonicus. This species occurs at the habitats from fine particle mud to gravels in coastal zone, and feeds on the surface sediment and detritus from seaweed. It is known that individuals of S. japonicus were divided into 3 morphological types according to their body colours (Green, Red and Black). The Green has a preference to habitat on sand and muddy-sand grounds, while Red lives mainly in the rock, pebble and gravel grounds (Choe and Ohshima, 1961). They are also known to be one of the conspicuous species that feed sediment on the bottom. They feed deposited seston on the substrate with their tentacles as if they sweep the surface. Deposit-feeding animals like S. japonicus ingest the surface sediment and assimilated organic matter for respiration and growth, defecating fecal pellets. In addition to feeding behaviour, bioturbation of crawling behaviour on the surface may affect the characteristics of sediment. They have advantageous characteristics of relatively longer lifespan of about 4 years and fewer predators in the field. This species is known to have seasonal cycle with a vigorous feeding activity in winter and an inactivity in summer...


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