Syms Craig, Jones Geoffrey P
Department of Marine Biology, James Cook University of North Queensland, Townsville, Queensland, 4811, Australia.
Oecologia. 2001 May;127(4):560-571. doi: 10.1007/s004420000617. Epub 2001 May 1.
Correlations between abundance of organisms and their habitat have often been used as a measure of the importance of particular habitat features. However, experimental manipulation of the habitat provides a more unequivocal estimate of its importance. In this study we quantified how fish communities on small patch reefs covaried with changes in benthic cover habitat features. A random sample of small patch reefs was selected and both fish abundance and habitat measures recorded. Naturally occurring patch reefs could be classed into three habitat types based on their benthic cover. Reefs dominated by massive soft corals were the most abundant (50%), followed by those dominated by rock and soft corals in equal proportions (36%), then reefs dominated by branching corals (14%). Fish assemblages differed between the reef types. Communities on soft-coral-dominated and rock/soft-coral-dominated patch reefs formed a continuum of species responses correlated with degree of soft coral cover. In contrast, branching-coral-dominated reefs were occupied by a more discrete set of species. We tested the role of soft corals in contributing to this pattern by experimentally reducing soft coral cover on patch reefs from a baseline level of ~67% to ~33% and ~6%, and monitoring the experiment over 2 years. Contrary to expectations derived from the correlative data, and in contrast with previous manipulations of hard corals, soft-coral disturbance did not generate any corresponding changes in the fish assemblage. This "negative" result indicated that the quality and heterogeneity of habitat generated by soft corals on patch reefs was indistinguishable from equivalent-sized habitat patches formed by bare rock alone. Nevertheless, because soft corals are living organisms they have the potential to generate indirect effects by interacting with other organisms such as hard corals. In the long-term, we hypothesize that biotic interactions between habitat forming organisms might affect composition of fish assemblages on patch reefs.
生物体数量与其栖息地之间的相关性常常被用作衡量特定栖息地特征重要性的指标。然而，对栖息地进行实验性操纵能更明确地评估其重要性。在本研究中，我们量化了小型斑块礁上的鱼类群落如何随底栖覆盖栖息地特征的变化而协变。选取了小型斑块礁的随机样本，并记录了鱼类数量和栖息地测量数据。根据底栖覆盖情况，自然形成的斑块礁可分为三种栖息地类型。以块状软珊瑚为主的礁最为丰富（50%），其次是岩石和软珊瑚比例相等的礁（36%），然后是以分支珊瑚为主的礁（14%）。不同类型的礁上鱼类组合有所不同。以软珊瑚为主和以岩石/软珊瑚为主的斑块礁上的群落形成了与软珊瑚覆盖程度相关的连续物种反应。相比之下，以分支珊瑚为主的礁则被一组更为离散的物种占据。我们通过实验将斑块礁上的软珊瑚覆盖从约67%的基线水平减少到约33%和6%，并在两年内监测该实验，以测试软珊瑚在形成这种模式中的作用。与从相关数据得出的预期相反，与之前对硬珊瑚的操纵不同，软珊瑚干扰并未在鱼类组合中产生任何相应变化。这个“负面”结果表明，斑块礁上软珊瑚产生的栖息地质量和异质性与仅由裸岩形成的同等大小的栖息地斑块没有区别。然而，由于软珊瑚是活的生物体，它们有可能通过与其他生物体（如硬珊瑚）相互作用而产生间接影响。从长远来看，我们假设形成栖息地的生物体之间的生物相互作用可能会影响斑块礁上鱼类组合的组成。
