Cowen Robert K
Scripps Institution of Oceanography, University of California, Mail Code A-008, 92093, La Jolla, CA, USA.
Oecologia. 1983 May;58(2):249-255. doi: 10.1007/BF00399225.
An experimental evaluation of the effect of sheephead (Semicossyphus pulcher) predation on red sea urchins (Strongylocentrotus franciscanus) was initiated at San Nicolas Island, California in Sept. 1980. All sheephead (N=220) were removed from an area of approximately 12,700 m and subsequent changes in sea urchin numbers and microhabitat utilization were monitored along permanent transects for 24 months. The sea urchins within the transects were also measured in situ to determine changes in the size frequency distribution of the population. Although sea urchins rank only seventh in relative importance in the sheephead's diet at San Nicolas Island, there has been a significant increase in sea urchin numbers in the experimental area (26% increase/year) but there has been no change in the control site. Further, there has been a slight increase in the proportion of sea urchins occupying exposed versus sheltered microhabitats in the removal site. Changes in the size frequency distribution of the urchins were minimal (probably due to an observation period of only one year); the size frequency distribution was unimodal and skewed to the left, indicating weak recruitment of urchins. Comparisons of sheephead densities and the percent of sea urchins in exposed microhabitats (i.e. available to predation by sheephead) were also made at four areas around San Nicolas Island and three areas in Baja California. In areas with low sheephead densities (0-35/hectare) sea urchins were highly exposed, and in areas where sheephead densities were high (200-500/hectare), no urchins were exposed.This study demonstrates that sheephead are capable of regulating the density and microhabitat distribution of sea urchin populations. These results are discussed in relation to other factors which may affect sea urchin populations.
1980年9月，在加利福尼亚州的圣尼古拉斯岛开始了一项关于羊头鱼（Semicossyphus pulcher）捕食对红海胆（Strongylocentrotus franciscanus）影响的实验评估。在大约12700平方米的区域内捕尽了所有羊头鱼（N = 220），并沿着永久性样带监测海胆数量和微生境利用情况的后续变化，为期24个月。还对样带内的海胆进行了实地测量，以确定种群大小频率分布的变化。尽管在圣尼古拉斯岛，海胆在羊头鱼的食物中相对重要性仅排名第七，但实验区域内海胆数量显著增加（每年增加26%），而对照地点则没有变化。此外，在移除羊头鱼的区域，占据暴露微生境与遮蔽微生境的海胆比例略有增加。海胆大小频率分布的变化很小（可能是由于观察期仅一年）；大小频率分布为单峰且向左偏斜，表明海胆补充率较低。还在圣尼古拉斯岛周围的四个区域和下加利福尼亚州的三个区域对羊头鱼密度和暴露微生境中海胆的百分比（即可被羊头鱼捕食的海胆）进行了比较。在羊头鱼密度低的区域（0 - 35/公顷），海胆高度暴露，而在羊头鱼密度高的区域（200 - 500/公顷），没有海胆暴露。这项研究表明，羊头鱼能够调节海胆种群的密度和微生境分布。结合可能影响海胆种群的其他因素对这些结果进行了讨论。
