上海芦潮港海岸带有孔虫种群动态与埋葬群形成

POPULATION DYNAMICS AND THANATOCOENOSE FORMATION OF RECENT LITTORAL FORAMINIFERA FROM LUCHAOGANG,SHANGHAI

通过季节采样和定量分析,研究了上海芦潮港海岸带表层沉积物中的有孔虫。研究表明:(1)芦潮港潮上和潮间带活有孔虫群落和种群具强烈的季节变化,但其组成、丰度和分异度与水温和盐度无明显的相关性。群落组成在潮上带以胶结质壳占优势,在潮间带则以钙质壳为主,但两者的丰度均在5—6月最高,8月前后最低。(2)根据壳体大小的频率曲线,推断Ammonia beccarii和Miliammina fusca两个种群一年至少有两个繁殖周期;A.beccarii种群具明显的世代交替:12—4月以微球型为主,5—11月以显球型为主。(3)潮间带埋葬群极大地不同于生物群,但变化幅度较小,组成以外来的异地分子占绝对优势;原地分子无论在种数和丰度上只占极小比例,并且在埋葬过程中丧失了大部分壳壁脆薄的成员。

In 1982, monthly samples of surface sediments (top 1cm)were taken from two sites ofthe littoral zone at Luchaogang,southeast of Shanghai,the eastern end of the subaerial deltaof the Changjiang (Yangtze)River. Site A is in the upper part of the intertidal zone withsalinity ranging from 2‰(September) to 16. 5‰(February) and water temperature from9. 2℃ (January)to 32. 2℃ (August), while Site B in a canal of the supratidal zone coveredwith perennial water where the salinity ranges from 1. 37‰ (October)to 2. 36‰(April)andthe temperature from 5. 6℃ (January)to 35. 8℃ (August). The living assemblage consists of12 brackish--water or euryhaline species, while the dead assemblage is composed of over 43species of both stenohaline marine and euryhaline species. Seasonal changes of foraminiferal communities Site A (intertidal zone) (Fig. 1, Table 1)The living assemblage is dominated by calcare-ous brackish--water species,although two of the 7 species in the community have arenaceoustests. The most abundant species is Ammonia beccarii (Linne) (54. 5% on the average),fol-lowed by Pseudononion minutum Zheng (20. 3%) and Protelphidium glabrum (He, Hu etWang) (15. 6%). A. beccarii reaches its abundance peak in winter(January and February),P.glabrum in autumn (October and November)and early winter(December),while P. minutumhas a more or less uniform seasonal distribution. There is conspicuous seasonal contrast inabundance of living foraminifers,ranging from 0. 8 specimens per 10ml of sample in Augustto 138 specimens per 10ml in June. Species diversity H(S)is higher in the period from June toNovember(1. 2)and lower from December to May(0. 9). Site B(supratidal zone) (Fig. 2, Table 2) The living assemblage is dominated by the are-naceous foraminifera Miliammina fusca and M. sp. A(both accounting for 79. 5%),with Julyas an exception when Protelphidium glabrum and other calcareous forms predominate. De-spite the greater number of living species (0. 8 on the average)than at Site A(0. 9),due to thehigher predominance of Miliammina spp. in the community,the maximum predominance oc-curs from September to December and in March,April and June when Miliammina exceeds85% of the population. In short,foraminiferal communities in both sites display significant seasonal variations, and the foraminiferal abundance reaches its maximum in May and June for both sites;whileminimal abundance occurs around August. Population dynamics Of the 12 species studied,only two are abundant enough for analysis of population dy-namics. Miliammina fusca (Figs. 3, 4)——Judging from its size distribution, the juvenile formsappeared in October and May,with test size increasing towards April and August. Ammonia beccarii (Figs. 5, 6)——A seasonal change in two types of this species hasbeen found; the microspheric form predominates during the period from December to March,and the megalospheric form in the remaining months,perhaps except for the high summerwhen the number of specimens was too limited to make analysis. Both forms display seasonalchanges in test size,with juvenile forms appearing mostly in March and November and withthe average maximum test size in July and February. Thanatocoenose formation The dead assemblages at Site A were quantitatively and qualitatively analyzed and com-pared with the living assemblages. It was found that the former are predominated by exoticforms of both stenohaline and brackish--water species,making up on the average 91. 0% ofthe total dead population. The common species are Epistominella naraensis(Kuwano) (22. 0%on the average), planktonic forms (13. 5%), Ammonia convexidorsa Zheng, and Elphidiummagellanicum Heron--Allen et Earland,all with tiny and floating tests. Our previous studiesshow that these forms are transported by the tidal currents in the estuary area. As shown infig. 7,the dead assemblage does not show significant variations in species composition andtest size as in the living population, but the abundance varies greatly with hydrodynamic con-ditions. The autochthonous forms make up a minor portion of the dead assembl