推荐回答(1个)
造礁珊瑚与非造礁珊瑚在海域中食物的来源并不相同。动物性浮游生物为珊食物的主要来源之一,但由于在热带珊瑚礁海域中动物性浮游生物较少,是以除了动物性浮游生物外,石珊瑚利用体内共生藻所产生的有机质以及海中颗粒状或溶解的有机物质来补充实营养上的需要;此外水螅体亦可利用溶解在水中的葡萄糖,并具有消化吸收浮游性细菌及溶解的有机蛋白质的能力。 严格来说,珊瑚并非滤食者,它依赖着经过自身的流水来捕捉悬浮在水中的物质,本身并无法鼓动水流达成滤食的目的,仅论其摄食行为可分为五类: 1)利用触手捕食。珊瑚的触手依种类而有不同的大小及活动程度。对所有的八放珊瑚而言,它们共同的摄食方式为:由水螅体的触手与羽状分枝快速地回旋捉取食物,当与食物接触时,触手马上迅速向前弯曲将食物送入张开的口部,然后由口与咽内的纤毛环流进行吞咽。六放珊瑚的触手绝大部份短而缺乏灵敏度,当摄食行为发生时,纤毛仅扮演着清除的角色,触手上的刺细胞在攫取食物后,便由触手弯曲送入口内。 2)利用纤毛与黏液捕食。石珊瑚的纤毛分怖在外胚层的支持细胞上,当摄食行为发生时,纤毛前后上下摆动,伴随着黏液的分泌,达到摄食或清除表面的目的。此类珊瑚,或是利用刺细胞捕食后由纤毛送至触手入口;或是食物由触手捕捉后交由纤毛送入口中;或是触手太小无法捕捉食物而由纤毛运动取代;或是由纤毛环流来捕食,触手只管接受或排除颗粒物质。软珊瑚大多数缺乏此种机制,而由密围在口部的纤毛催动水流入口中。 3)利用伸出的消化丝捕食。消化丝位于珊瑚水螅体的消化循环腔中,当食物颗粒与外胚层接触时,消化丝便会伸出,此种刺激消化丝伸出的行为包含了触觉和化学交错的反应。 4)利用黏丝网捕食。利用此法的珊瑚只有在晚上摄食,珊瑚虫体会分泌黏液,一端形成由黏丝组成的网状,另一端则附着在虫体上,当水中浮游生物或有机碎片流过时就会黏着在黏丝网上;每隔一段时间,虫体就会将这些黏丝网收回吞食,消化附着在上面的营养物。 5)吸收。在石珊瑚外胚层细胞中具有纤毛,且有大量的碱性磷酸酵素,专司肠系膜的伸展和控制腔肠外的消化与吸收;软珊瑚的圆盘及触手上没有纤毛,代之以具吸收功能的绒毛。 除了这些主动摄食行为外,珊瑚体内的共生藻也提供了珊瑚虫部份的营养来源,这可分为两类,一为藻类行光合作用后分泌出来的有机物质,以多醣类及甘油分子为主;另一类是共生藻老化后在珊瑚体内死亡分解,经由细胞内消化的作用而成为宿主的营养来源。
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