Andrew N L, Choat J H
Leigh Marine Research Laboratory, University of Auckland, New Zealand.
Department of Zoology, University of Auckland, New Zealand.
Oecologia. 1982 Jan;54(1):80-87. doi: 10.1007/BF00541113.
Reefs dominated by red algae, associated with high echinoid densities, are consistent features of the shallow subtidal around northeastern New Zealand. Factors determining the abundance of juvenile Evechinus chloroticus were investigated in such a habitat. Using a factorial design, a field experiment was used to assess the influence of predators and adult E. chloroticus on juvenile abundance. The use of 2 m exclusion cages enhanced juvenile E. chloroticus abundance over a 16 month period, an effect independent of conspecific adults. We attributed this effect to the exclusion of benthic-feeding, predatory fish. Several species forage over the study area at high densities and are known from gut content analysis to prey on juvenile E. chloroticus in the field. Invertebrate predators are at very low densities in the area. The possibility of caging and site artefacts confounding this interpretation is discussed.Adult E. chloroticus did not directly affect conspecific juvenile densities during the experimental period. However their removal produced a significant change in community structure toward one dominated by macroscopic brown algae. Echinoid removal led to rapid recruitment of laminarian and fucoid algae, predominantly Ecklonia radiata and Sargassum sinclairii. In addition, densities of herbivorous gastropods, particularly the limpet Cellana stellifera decreased in the echinoid exclusion area, as did the feeding rates of predatory fish. The consequences of E. chloroticus removal may be dependent upon the size of the area from which they are excluded.Despite the high densities of predatory fish, a low though consistent number of juvenile E. chloroticus escape predation. We suggest that these represent sufficient input into the adult grazing population to maintain the habitat. This interpretation argues against a key role for predators in structuring shallow water reef communities in northeastern New Zealand.
由红藻主导、海胆密度较高的珊瑚礁是新西兰东北部浅潮下带的常见特征。在这样的栖息地中，研究了决定绿海胆幼体数量的因素。采用析因设计，通过田间实验评估捕食者和成年绿海胆对幼体数量的影响。在16个月的时间里，使用2米的隔离网箱提高了绿海胆幼体的数量，这一效果与同种成年个体无关。我们将这种效果归因于底栖摄食性捕食鱼类的排除。几种鱼类在研究区域高密度觅食，通过肠道内容物分析可知它们在野外捕食绿海胆幼体。该区域的无脊椎动物捕食者密度非常低。讨论了网箱和地点假象混淆这一解释的可能性。在实验期间，成年绿海胆没有直接影响同种幼体的密度。然而，它们的移除导致群落结构发生显著变化，向以大型褐藻为主导的群落转变。海胆的移除导致海带和墨角藻迅速繁殖，主要是辐射石莼和辛氏马尾藻。此外，食草性腹足类动物的密度，特别是星状笠贝的密度在海胆排除区域有所下降，捕食性鱼类 的摄食率也下降了。绿海胆移除的后果可能取决于它们被排除的区域大小。尽管捕食性鱼类密度很高，但仍有少量但数量稳定的绿海胆幼体逃脱了捕食。我们认为，这些幼体为成年放牧种群提供了足够的补充，以维持栖息地。这一解释反对捕食者在构建新西兰东北部浅水珊瑚礁群落中起关键作用的观点。
