Speaker： Jianhu

East China Sea Fisheries Research Institute Dalian 10.31

Seasonal Changes in the Ecological Characteristics of Pelagic Molluscs in the Changjiang Estu

ary

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

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.

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°E

Changjiang Estuary

Shanghai

Data Processing

Index of clumping

Dominance (Y)

Shannon-Wiener ( )

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Horizontal distribution of the total abundance121 121.5 122 122.5 123 123.5121 121.5 122 122.5 123 123.5

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Spring Summer

°N°E

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.

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Autumn Winter

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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.

Horizontal distribution of the total abundance

Seasonal variation of pelagic molluscs ab

undance,temperature, salinity

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).

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8温度 盐度 平均丰度Temperature AbundenceSalinity

spring winterautumnsummer

Seasons dominant species Y β t P

SpringLimacina trochiformis 0.27 0.86 22.56 0.0001

Peraclis reticulata 0.02 0.56 14.82 0.0001

SummerAtlanta peroni 0.16 0.92 12.11 0.0001

Creseis acicula 0.10 0.01 0.17 0.8627

Autumn

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

Winter Agadina stimpsoniji 0.03 0.99 ＞ 100 0.0001

Contribution of dominant species to total abundance of pelagic mollusks

Relationship of pelagic mollusc abundance, surface salinity and temperature

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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 abundanc℃e is relatively low.

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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 highes℃t abundance of Agadina stimpsoniji occurred in the area with the surface water temperature 18.43 , salinity in 9.14. ℃

Species Spring Summer Autumn Winter

Agadina stimpsoniji ＋ ＋ ＋ ＋

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.