Levin P, Petrik Rachel, Malone John
Department of Marine Biology, Texas A&M University -Galveston, P.O. Box 1675, Galveston, TX 77553-1675, USA, , , , , , US.
Oecologia. 1997 Sep;112(1):55-63. doi: 10.1007/s004420050283.
Seagrass meadows are often important habitats for newly recruited juvenile fishes. Although substantial effort has gone into documenting patterns of association of fishes with attributes of seagrass beds, experimental investigations of why fish use seagrass habitats are rare. We performed two short-term manipulative field experiments to test (1) the effects of food supply on growth and densities of fish, and (2) effects of predation on the density and size distribution of fish recruits, and how this varies among habitat types. Experiments were conducted in Galveston Bay, Texas, and we focused on the common estuarine fish, pinfish Lagodon rhomboides. In the first experiment, replicate artifical seagrass and sand plots were either supplemented with food or left as controls. Recruitment of pinfish was significantly greater to seagrass than sand habitats; however, we detected no effect of food supplementation on the abundance of recruits in either habitat. Pinfish recruits in artifical seagrass grew at a significantly faster rate than those in sand habitats, and fish supplemented with food exhibited a greater growth rate than controls in both sand and artifical grass habitats. In our second experiment, we provided artificial seagrass and sand habitats with and without predator access. Predator access was manipulated with cages, and two-sided cages served as controls. Recruitment was significantly greater to the cage versus cage-control treatment, and this effect did not vary between habitats. In addition, the standard length of pinfish recruits was significantly larger in the predator access than in the predator exclusion treatment, suggesting size-selective predation on smaller settlers or density-dependent growth. Our results indicate that the impact of predation on pinfish recruits is equivalent in both sand and vegetated habitats, and thus differential predation does not explain the higher recruitment of pinfish to vegetated than to nonvegetated habitats. Since predators may disproportionately affect smaller fish, and a limited food resource appears to be more effectively utilized by fish in vegetated than in unvegetated habitats, we hypothesize that pinfish recruits may select vegetated habitats because high growth rates allow them to achieve a size that is relatively safe from predation more quickly.
海草草甸通常是新招募的幼鱼的重要栖息地。尽管已经付出了巨大努力来记录鱼类与海草床特征的关联模式，但关于鱼类为何利用海草栖息地的实验研究却很少。我们进行了两项短期操纵性野外实验，以测试：（1）食物供应对鱼类生长和密度的影响；（2）捕食对幼鱼密度和大小分布的影响，以及这种影响在不同栖息地类型之间如何变化。实验在得克萨斯州加尔维斯顿湾进行，我们重点研究了常见的河口鱼类——菱体兔牙鲷。在第一个实验中，对重复的人工海草和沙地试验区要么补充食物，要么作为对照。菱体兔牙鲷在海草栖息地的幼鱼补充量显著高于沙地栖息地；然而，我们未检测到食物补充对任何一个栖息地幼鱼数量的影响。人工海草中的菱体兔牙鲷幼鱼生长速度明显快于沙地栖息地中的幼鱼，并且在沙地和人工海草栖息地中，补充食物的鱼类比对照鱼类表现出更高的生长速度。在我们的第二个实验中，我们为人工海草和沙地栖息地设置了有捕食者进入和无捕食者进入的情况。通过笼子来控制捕食者的进入，双侧笼子作为对照。与笼子对照处理相比，笼子处理的幼鱼补充量显著更高，并且这种影响在不同栖息地之间没有差异。此外，有捕食者进入时菱体兔牙鲷幼鱼的标准长度显著大于捕食者排除处理时的长度，这表明对较小定居者存在大小选择性捕食或密度依赖性生长。我们的结果表明，捕食对菱体兔牙鲷幼鱼的影响在沙地和植被栖息地中是相同的，因此不同的捕食情况并不能解释菱体兔牙鲷在植被栖息地比非植被栖息地有更高的幼鱼补充量。由于捕食者可能对较小的鱼类产生不成比例的影响，并且有限的食物资源似乎在植被栖息地中比在非植被栖息地中能被鱼类更有效地利用，我们推测菱体兔牙鲷幼鱼可能选择植被栖息地，因为高生长速度使它们能够更快地达到相对安全的大小，从而免受捕食。
