大型海藻在珊瑚礁退化过程中的作用

随着全球范围珊瑚礁的退化,大型海藻在珊瑚礁区的覆盖度呈增多的趋势。大型海藻的大量生长,妨碍了珊瑚的生长、繁殖、恢复等过程。概括起来,大型海藻对珊瑚生长、繁殖及恢复过程所产生的不利影响主要包括:(1)大型海藻通过与珊瑚竞争空间和光照而影响珊瑚生长;(2)大型海藻与珊瑚直接接触时,通过摩擦作用及释放化感物质而影响珊瑚生长;(3)大型海藻的大量生长打破了珊瑚与海藻的竞争平衡,珊瑚为应对大型海藻的入侵而把用于生长和繁殖的能量转移到组织修复与防御上,进而造成珊瑚繁殖能量的减少;(4)大型海藻通过影响珊瑚幼虫的附着及附着后的存活率,而阻碍珊瑚群落的发展;(5)海藻还能通过富集沉积物、释放病原体及扰乱珊瑚共生微生物的生长等而间接影响珊瑚生长。明确的竞争机制有利于研究海藻与珊瑚的相互作用过程。在总结前人对海藻与珊瑚的竞争机制研究的基础上,把两者的竞争机制划分成物理机制、化学机制、微生物机制三大类,物理机制是研究得比较透彻的竞争机制,而化学机制与微生物机制则需要更深入的研究,是当前研究的热点。目前,我国对珊瑚礁中底栖海藻与珊瑚的相互作用研究甚少;鉴于此,对底栖海藻功能群的划分类型以及三大类型底栖海藻对珊瑚的作用特点做了简要介绍,并对珊瑚礁退化的现状和退化珊瑚礁区内海藻的表现做了概述。在此基础上,再综述国外关于大型海藻对珊瑚的影响研究进展,指出我国应该加强对南海珊瑚礁区大型海藻的种类分布及丰富度等的调查,评价大型海藻对南海珊瑚礁的影响现状;并结合生理学、分子生物学技术和生态学研究手段,在细胞与分子水平上探索海藻对珊瑚的影响机制,以期为珊瑚礁生态系统的保护提供参考。

Review on the effect of macroalgae on the degeneration of coral reefs

In light of the global scope of coral reefs degradation, macroalgae cover is becoming increasingly common in reef regions. The overgrowth of macroalgae in reef regions hampers the growth, reproduction and recovery of coral colonies, primarily because: (1) macroalgae compete with corals for space and light, lowering the growth rate of corals, causing death through suffocation and inhibiting the engraftment of coral larvaes; (2) macroalgae negatively affect corals growth via physical abrasion and the release of allelochemicals when in direct contact with corals; abrasion causes coral polyps to shrink and influences the ingestion behaviour and calcification of polyps, while the release of allelochemicals into the surrounding environment of corals may cause coral bleaching and the damage of coral tissue. (3) The reproduction of corals is a highly energy consuming process. Any outside pressure which may drain a coral''s stored energy will influence the fertility of the coral. In reef regions, the overgrowth of macroalgae breaks its competitive balance with corals, since, in response to the invasion of macroalgae, corals re-allocate energy needed for growth and reproduction to tissue repair and protection, causing a decrease in the quantity and quality of coral eggs, which decreases the energy allocated to reproduction; (4) The inhibiting effects of macroalgae on corals is the key factor to cause the degeneration of coral communities. Macroalgae influence the settlement and survival rate of coral larvas, thereby preventing the development of coral communities; (5) seaweeds accumulate sediments, release pathogens, and disrupt the growth of coral symbiotic microbes, indirectly influencing coral growth. This paper includes a brief overview of the primary competitive mechanisms (physical, chemical, and microbial) of macroalgae and corals. Understanding these competitive mechanisms will be very helpful when studying the interaction process between macroalgae and corals. We know much about the physical competition mechanisms, but the chemical and microbial mechanisms require more in-depth research; indeed, they are the hotspot of current research in coral reef sciences. In addition, this paper categorizes macroalgae according to their functional groups, lists the effects of three types of benthic seaweeds on corals, and summarizes the present status of coral reef degradation and the effect of macroalgae in areas with degraded reefs. Finally, it includes a review of the progress made by the latest research on the effect of macroalgae on corals, and suggests that our study should strengthen its research on the distribution and abundance of macroalgae species in the coral reef regions of the South China Sea in order to better evaluate the extent of macroalgae influence on the coral reefs of this region. Physiological, molecular, and ecological methods should be utilized to explore the mechanisms via which macroalgae influence corals at the cellular and molecular levels, in order to provide reference data for coral reef ecosystem conservation.