McClanahan T R, Shafir S H
Center for Wetlands, University of Florida, 32611, Gainesville, FL, USA.
Coral Reef Conservation Project, P.O. Box 99470, Mombasa, Kenya.
Oecologia. 1990 Jun;83(3):362-370. doi: 10.1007/BF00317561.
Large differences in community structure of sea urchins and finfish have been observed in Kenyan reef lagoons. Differences have been attributed to removal of finfish predators through human fishing activities. This study attempted to determine (i) the major sea urchin finfish predators, (ii) the effect of predation on sea-urchin community structure, and (iii) the possible effect of sea urchin increases and finfish decreases on the lagoonal substrate. Six reefs, two protected and four unprotected, were compared for differences in finfish abundance, sea urchin abundance and diversity and substrate cover, diversity and complexity. Comparisons between protected and unprotected reefs indicated that finfish populations were ca. 4 x denser in protected than unprotected reefs. Sea urchin populations were >100 x denser and predation rates on a sea urchin, Echinometra mathaei, were 4 x lower in unprotected than in protected reefs. The balistidae (triggerfish) was the single sea-urchin finfish predator family which had a higher population density in protected than in unprotected reefs. Balistid density was positively correlated with predation rates on tethered E. mathaei (r=0.88; p<0.025) and negatively correlated with total sea-urchin density (r=-0.89; p<0.025) on the six reefs. We conclude from observations that the balistids Balistaphus undulatus and Rhinecanthus aculeatus are the dominant sea-urchin predators. The sea-urchin assemblage had its greatest diversity and species richness at intermediate predation rates and low to intermediate sea-urchin densities. At low predation rates and high sea-urchin density E. mathaei dominated the assemblage's species composition. Preferential predation on the competitive dominant maintains the assemblage's diversity, supporting the compensatory mortality hypothesis (Connell 1978) of coral reef diversity. Protected reefs had greater cover of hard coral, calcareous and coralline algae, and greater substrate diversity and topographic complexity than unprotected reefs which had greater algal turf and sponge cover. Coral cover and topographic complexity were negatively correlated with total sea urchin density. Although experimentation is lacking, these substrate changes may be due to the switch from finfish to sea-urchins as consumers which results from overfishing of finfish. Removal of top invertebrate-eating carnivores appears to have cascading effects on the entire coral reef ecosystem.
在肯尼亚的珊瑚礁泻湖中，已观察到海胆和有鳍鱼类的群落结构存在巨大差异。这些差异被归因于人类捕鱼活动导致有鳍鱼类捕食者的减少。本研究试图确定：（i）主要的海胆有鳍鱼类捕食者；（ii）捕食对海胆群落结构的影响；（iii）海胆数量增加和有鳍鱼类数量减少对泻湖基质可能产生的影响。对六个珊瑚礁进行了比较，其中两个为受保护的，四个为未受保护的，比较内容包括有鳍鱼类的丰度、海胆的丰度和多样性以及基质覆盖度、多样性和复杂性。受保护和未受保护珊瑚礁之间的比较表明，受保护珊瑚礁中的有鳍鱼类种群密度约为未受保护珊瑚礁的4倍。海胆种群密度在未受保护的珊瑚礁中比受保护的珊瑚礁高100倍以上，并且在未受保护的珊瑚礁中，对海胆马氏长海胆（Echinometra mathaei）的捕食率比受保护的珊瑚礁低4倍。鳞鲀科（扳机鱼）是唯一一种在受保护珊瑚礁中种群密度高于未受保护珊瑚礁的海胆有鳍鱼类捕食者家族。在这六个珊瑚礁上，鳞鲀科的密度与拴系的马氏长海胆的捕食率呈正相关（r = 0.88；p < 0.025），与海胆总密度呈负相关（r = -0.89；p < 0.025）。根据观察结果，我们得出结论，波纹短吻三刺鲀（Balistaphus undulatus）和尖吻鲀（Rhinecanthus aculeatus）是主要的海胆捕食者。海胆组合在中等捕食率以及低到中等海胆密度时具有最大的多样性和物种丰富度。在低捕食率和高海胆密度时，马氏长海胆在组合的物种组成中占主导地位。对竞争优势种的优先捕食维持了组合的多样性，支持了珊瑚礁多样性的补偿性死亡率假说（Connell，1978年）。与未受保护的珊瑚礁相比，受保护的珊瑚礁有更大面积的硬珊瑚、钙质和珊瑚藻覆盖，并且基质多样性和地形复杂性更高，而未受保护的珊瑚礁则有更多的藻皮和海绵覆盖。珊瑚覆盖度和地形复杂性与海胆总密度呈负相关。尽管缺乏实验验证，但这些基质变化可能是由于过度捕捞有鳍鱼类导致消费者从有鳍鱼类转向海胆所致。顶级无脊椎动物食肉动物的移除似乎对整个珊瑚礁生态系统产生了连锁反应。
