Organic matter flow in the benthic detritivores of the Chuwei mangrove swamp in the Tanshui estuary: a stable isotope study

• Main Authors: Yang, Hsiao-hui, 楊小慧
• Other Authors: Chen Chang-po
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/07588562663598807176

碩士 === 國立臺灣大學 === 漁業科學研究所 === 86 === In the mangrove estuary of the Tanshui River in northern Taiwan, the comp onents of the detrital food chain, including the particulate organic matter (P OM) of sea water, river water and sediment, primary producers, deposit feeders , and a suspension feeder, were examined at three sites using stable carbon an d sulfur isotopes to reveal the possible flow of organic matter. The fresh le aves of the vascular plant Kandelia candel had a δ13C as -26.2 %, indicating that it is a C3 plant. K. candel had a δ34S value of +5.6 %. The δ13C leve l of particulate organic matter (POM) of sea water (collected at flood tides) averaged -23.5 %, and that of river water (collected at ebb tides) was -24.6 %, whereas benthic microalgae had a δ13C level of -19.4 %. The δ13C and δ3 4S levels of sediments ranged from -26.1 to -24.6 % and +5.0 to + 9.1 %, respe ctively, and were close to the values of the mangal leaves, suggesting that th e organic source of sediments comes mainly from the vascular plant K. candel. The isotopic values of the sediment did not significantly differ according to the site (3 sites) or the depth (2 depths), but differ according to particle size. These results indicate that particle size is a key factor in harboring different sources of organic matter. In polychaetes, the deposit feeder (the nereid Neathes glandicincta), and the suspension feeder (the sabellid Laonome albicingillum) had δ13C values ranging from -21.4 to -20.8. %, and from -22.2 to -21.9 %, respectively; whereas δ34S values ranged from +8.6 to +13.8 %, a nd +10.2 to +11.7 %, respectively. The two polychaetes significantly differed in their stable isotopic compositions and N. glandicincta was at slightly hig her trophic rank than L. albicingillum. In addition, the nereids exhibited a greater variation in the sources of the detrital organic matter than the sabel lids. Based on the δ13C and δ34S values, the crabs were well separated into three groups, also according to the sites. The river living crabs containing Uca arcuata and U. lactea had δ13C values averaged -15.5 % and δ34S values averaged +13.1 %, the creek living crabs containing U. arcuata again and U. b orealis had -19.4 % and +11.7 %, and the creek living Helice. formosensis as - 21.5 % and +9.9 %, respectively. Such a discrepancy found in the detritivores may be attributed to their different feeding sites and modes. The present st udy suggests that the detritus consumed by the two studied polychaete species and H. formosensis are probably from K. candel and POM of water. As regards t he food of the crabs, both benthic microalgae and Phragmites commuuis are poss ible sources and the relative importance of the two sources depends on where t he crabs live. In conclusion, detrtus in the study mangrove swamp are disting uishable from one another and detritivores differentiate their food sources fr om a common pool.