盐度与种间竞争对漂浮生态型浒苔微繁体萌发和生长的影响

EFFECTS OF SALINITY AND INTERSPECIES COMPETITION ON PROPAGULE GERMINATION AND SEEDLING GROWTH OF FLOATING ECOTYPE OF ULVA PROLIFERA

黄海绿潮源自苏北浅滩,暴发后期浒苔向北漂移至山东半岛南岸,会集中释放大量微繁体。虽然构成严重的繁殖体压力,但尚未发生大面积定生。为了明确漂浮生态型浒苔北侵定居的关键限制因素,本研究于2015年7月漂浮浒苔在青岛沿海大量堆积期间,采集潮间带表层沉积物样本,分别在盐度25和32下进行培养,试验不同盐度对漂浮生态型浒苔微繁体萌发和幼苗生长的影响。进一步通过单藻种培养,分析漂浮生态型与定生浒苔群体、以及青岛定生近缘种缘管浒苔对盐度的适应性差异。结果表明,盐度对微繁体萌发与幼苗生长两个阶段均构成重要影响,但具有不同的影响方式。在萌发阶段,单藻培养条件下,盐度对浒苔各群体和缘管浒苔的萌发率均无显著影响,但在混合培养条件下,盐度则通过种间竞争对萌发率产生显著影响,青岛的高盐条件更加有利于当地种,而苏北海域的低盐条件会显著提高漂浮生态型的萌发率。在幼苗的生长阶段,盐度可直接产生影响,高盐条件显著降低浒苔所有群体幼苗的生长率,对缘管浒苔则无显著影响,表现明显的种间差异。上述结果提示,盐度与种间竞争的协同作用可能是限制漂浮生态型浒苔大规模北侵定居的重要因素,这为预测漂浮生态型的扩散范围与黄海绿潮的变异趋势提供了理论依据。

The Yellow Sea green tide has been found originated from the shoal of Jiangsu Province,China and drifted northward to the southern flank of Shandong at last.Despite the serious propagule pressure caused by the floating ecotype of U.prolifera,this ecotype has not yet established along the peninsula coast on a large scale.To identify the key factors that limited the northward colonization of floating ecotype,samples of surface sediments in the intertidal zone were collected in Qingdao in July 2015,when the floating ecotype of U.prolifera was accumulating on seashore.The effects of salinity on the germination rate and seedling growth of the floating ecotype were analyzed by culturing the sediment samples in salinity 25 and 32,respectively.In addition,the floating ecotype,an attached strain of U.prolifera,as well as an allied species U.linza were cultured individually to compare their adaptability to different salinity.The results show that salinity played an important role in propagule germination and seedling growth but in different ways.At the stage of propagule germination,salinity had no significant effect on the germination rate of all the Ulva strains tested when they were cultured individually.However,under mixed culture conditions,salinity had a significant effect on germination rate through interspecific competition.The higher salinity as in Qingdao was more favorable for local species,while the lower salinity as in shoal of Jiangsu could significantly increase the germination rate of floating ecotype of U.prolifera.In the stage of seedling growth,an obvious interspecific difference was noted that salinity could directly affect the growth rate of all U.prolifera strains but had no significant effect on U.linza.The results suggest that the synergism between salinity and interspecies competition may play an important role to restrict the northward colonization of floating ecotype of U.prolifera,which provides a theoretical basis for predicting the spreading range of the floating ecotype and the variation trend of the Yellow Sea green tide.