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Seasonal Changes in the Ecological Characteristics of Pelagic Molluscs in the Changjiang Estuary Speaker：Jianhu East China Sea Fisheries Research Institute Dalian 10.31 Outline Purpose and Significance Study area and sampling methods Results Conclusion There are two species belong to pelagic mollusks.One is Pteropoda, the other is Heteropoda. Pteropoda is a group of marine pelagic molluscs,which belongs to Opisthobranchia of Gastropoda. Heteropoda belong to Prosobranchia subclass, Gastropoda order. Study area and time 121 121.5 122 122.5 123 123.5 °E °N 32 Changjiang Estuary 31.5 31 Shanghai 30.5 30 29.5 29 The investigation was carried out in the East China Sea (28°30´~32°30´N、121°30´~123°30´E). Four sampling cruises are conducted separately in spring(May), summer(August), autumn(November) and winter(February-March) in 2002. Data Processing Index of clumping S2 I 1 X Dominance (Y) ni Y fi N s ' Shannon-Wiener (H ) ni ni H log 2 N i 1 N ' Horizontal distribution of the total abundance 121 °N 121.5 122 122.5 123 123.5 121 121.5 122 122.5 123 123.5 °E 32 31.5 31 30.5 30 29.5 29 Spring Summer In spring, pelagic molluscs aggregated in north nearshore where the Yellow Sea Coastal Current meets the Changjiang Diluted Water. Numerically, Limacina trochiformis and Peraclis reticulata were found to be the main component of the pelagic Molluscs. In summer, high abundance distribution area was located in the nearshore of Changjiang Estuary. Atlanta peroni and Creseis acicula were the main component of the pelagic Molluscs. Horizontal distribution of the total abundance 121 121.5 122 122.5 123 123.5 121 121.5 122 122.5 123 123.5 °E °N 32 31.5 31 30.5 30 29.5 29 Autumn Winter In autumn, pelagic molluscs were abundant in the water off Chowshan. where the Taiwan Warm Current met the Changjiang Diluted Water. Pelagic Molluscs were composed of Creseis acicula and Cavolinia tridentata. Species number was low in winter because most of the pelagic molluscs are warm water species. Seasonal variation of pelagic molluscs abundance,temperature, salinity Salinity 盐度 盐度 平均丰度abundence(ind/m3) Abundence(ind/m3) 平均丰度abundence(ind/m3) Abundence 平均丰度 平均丰度 35 35 88 77 30 30 66 25 25 5 5 20 20 4 15 4 3 15 10 23 10 5 12 05 01 spring summer autumn winter 夏季 秋季 冬季 0 春季 0 According to Fig, there was a obviously seasonally variation of average abundance. peaked in冬季 summer 春季The abundance 夏季 秋季 (7.11ind/m3), declined in autumn and reached the lowest in winter(0.05 ind/m3). 温度Temperature(℃) Temperature(℃) 温度Temperature(℃) Salinity(‰) 盐度 Sanity(‰) 盐度 Sanity(‰) Temperature 温度 温度 Contribution of dominant species to total abundance of pelagic mollusks Seasons Y β t P Limacina trochiformis 0.27 0.86 22.56 0.0001 Peraclis reticulata 0.02 0.56 14.82 0.0001 Atlanta peroni 0.16 0.92 12.11 0.0001 Creseis acicula 0.10 0.01 0.17 0.8627 Creseis acicula 0.16 0.21 21.00 0.0001 Cavolinia tridentata 0.10 0.80 89.81 0.0001 Agadina stimpsoniji 0.04 0.14 19.75 0.0001 Pneumodermopsis ciliata 0.02 0.05 7.76 0.0001 0.99 ＞100 0.0001 dominant species Spring Summer Autumn Winter Agadina stimpsoniji 0.03 Relationship of pelagic mollusc abundance, surface salinity and temperature 10 15 20 25 3010 15 20 25 30 T℃ S 30 25 20 15 10 5 Limacina trochiformis Creseis acicula Limacina trochiform was sensitive to temperature and it was more abundant at the sea surface temperature 17.5℃. As to Creseis acicula, it reached the peak of 4.2ind/m3 where the surface water temperature at 18.4 ℃, salinity at 15.4, in the other hydrological environment, the abundance is relatively low. 10 S 15 20 25 3010 15 20 25 30 T℃ 30 25 20 15 10 5 Atlanta rosea Agadina stimpsoniji The total abundance of Atlanta rosea have the highest value where the surface water temperature 25.7℃, salinity in 7.7. The highest abundance of Agadina stimpsoniji occurred in the area with the surface water temperature 18.43℃, salinity in 9.14. Species Agadina stimpsoniji Spring Summer Autumn Winter ＋ ＋ ＋ ＋ ＋ ＋ Abranchaea chinensis Atlanta lesueuri ＋ Atlanta rosea ＋ ＋ Atlanta peroni ＋ ＋ Atlanta inflata ＋ Cavolinia longirostris ＋ Cavolinia tridentata ＋ Corolla ovata ＋ Creseis sp. ＋ Creseis acicula ＋ ＋ ＋ ＋ Creseis virgula Creseis virgula v.comica ＋ Desmopterus papilio ＋ Limacina inflata ＋ Limacina bulimoides ＋ ＋ Limacina trochiformis ＋ ＋ Notobranchaea macdonaldi ＋ Oxygyrus eraudreni ＋ Paraclione longicaudata ＋ Peraclis reticulata ＋ ＋ ＋ ＋ ＋ ＋ Pneumodermopsis ciliata ＋ ＋ Pneumoderma atlanticum ＋ ＋ Protatlanta souleyeti ＋ Conclusion Temperature was a major factor influencing the seasonal changes of the total abundance. The distribution was mainly affected by salinity. Numerically, Limacina trochiformis was the dominant species in spring, which we attribute to its low temperature adaptation. Atlanta peroni was the dominant species in summer and Creseis acicula was the dominant species in autumn. These species are adapted to relatively high temperature. Agadina stimpsoniji, adapted to low temperature,was the dominant species in winter. Abundance and species number were lower nearshore than offshore in the East China Sea because most pelagic molluscs are offshore species.