River G F., Edmunds P J.
Department of Ecology and Evolutionary Biology, Box G-W, Brown University, 02912, Providence, RI, USA
J Exp Mar Biol Ecol. 2001 Jul 1;261(2):159-172. doi: 10.1016/s0022-0981(01)00266-0.
After several decades of disturbance, many coral reefs in the Caribbean are dominated by macroalgae. One process affecting this transition is coral-macroalgal competition, yet few studies have addressed the mechanisms involved. In this study, we investigated competition between the tall and bushy macroalga Sargassum hystrix (J. Agardh) and the branching coral Porites porites (Pallas) on a shallow reef in Jamaica. Experiments were designed to expose coral branches to different treatments to test the role of shading and abrasion by Sargassum on coral growth and polyp expansion. Corals exposed to Sargassum grew significantly more slowly (80% reduction) than controls, but this effect was absent when corals were caged to prevent physical contact with macroalgae. Light levels were reduced in both the algal and cage treatments, but shading apparently had little effect on the growth of corals in cages. Short-term measurements of integrated net water flow did not detect variation among treatments. In algal-mimic treatments, where clear plastic strips could touch but not shade the corals, growth rates were 25% lower than controls, but this effect was not statistically significant. Thus, the growth of corals in contact with Sargassum was reduced by abrasion and, to a lesser extent, by factors unique to living macroalgae. Analysis of polyp expansion showed that polyps were more frequently retracted when corals were in contact with macroalgae or algal-mimics compared to controls or cage treatment; the frequency of polyp contraction was correlated positively with growth. Together, these results suggest that abrasion-mediated polyp retraction is one of the primary mechanisms of competition utilized by tall (ca. 17 cm) macroalgae against scleractinian corals.
经过几十年的干扰，加勒比地区的许多珊瑚礁都被大型藻类所主导。影响这种转变的一个过程是珊瑚与大型藻类的竞争，但很少有研究探讨其中涉及的机制。在本研究中，我们调查了高大丛生的大型藻类多刺马尾藻（J. 阿加德）与分支珊瑚多孔鹿角珊瑚（帕拉斯）在牙买加一个浅礁上的竞争情况。实验设计是将珊瑚枝条暴露于不同处理下，以测试马尾藻的遮光和磨损对珊瑚生长及珊瑚虫扩张的作用。暴露于马尾藻的珊瑚生长速度明显比对照组慢（降低了80%），但当用笼子将珊瑚罩住以防止与大型藻类发生物理接触时，这种影响就不存在了。藻类处理组和笼子处理组的光照水平都降低了，但遮光显然对笼中珊瑚的生长影响不大。对综合净水流的短期测量未检测到各处理之间的差异。在藻类模拟处理中，透明塑料条可以接触但不会遮住珊瑚，其生长速度比对照组低25%，但这种影响在统计学上不显著。因此，与马尾藻接触的珊瑚的生长因磨损而降低，在较小程度上也受到活的大型藻类特有因素的影响。对珊瑚虫扩张的分析表明，与对照组或笼子处理相比，当珊瑚与大型藻类或藻类模拟物接触时，珊瑚虫更频繁地收缩；珊瑚虫收缩的频率与生长呈正相关。总之，这些结果表明，磨损介导的珊瑚虫收缩是高大（约17厘米）大型藻类对抗石珊瑚的主要竞争机制之一。
