Seasonal Ecological Characteristics of Pelagic Molluscs in Changjiang Estuary

1. Speaker：Jianhu East China Sea Fisheries Research Institute Dalian 10.31 Seasonal Changes in the Ecological Characteristics of Pelagic Molluscs in the Changjiang Estuary

2. Outline • Purpose and Significance • Study area and sampling methods • Results • Conclusion

3. 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.

4. °E °N Changjiang Estuary Shanghai Studyareaandtime 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.

5. Data Processing • Index of clumping • Dominance(Y) • Shannon-Wiener ( )

6. °E °N Spring Summer Horizontal distribution of the total abundance 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.

7. °E °N Winter Autumn Horizontal distribution of the total abundance 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.

8. Temperature Salinity Abundence Seasonal variation of pelagic molluscs abundance,temperature, salinity Temperature(℃) Salinity(‰) Abundence(ind/m3) spring summer autumn winter According to Fig, there was a obviously seasonally variation of average abundance. The abundance peaked in summer (7.11ind/m3), declined in autumn and reached the lowest in winter(0.05 ind/m3).

9. Contribution of dominant species to total abundance of pelagic mollusks

10. Relationship of pelagic mollusc abundance, surface salinity and temperature T℃ S 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.

11. T℃ S 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.

13. 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.

14. Thanks