Hay Mark E, Colburn Tina, Downing Daphne
Institute of Marine Sciences, University of North Carolina at Chapel Hill, 28557, Morehead City, NC, USA.
, P.O. Box 186, 42029, Calvert City, KY, USA.
Oecologia. 1983 Jun;58(3):299-308. doi: 10.1007/BF00385227.
Blades of Thalassia testudinum Banks ex König were used in a field bioassay to assess the impact of herbivorous fishes and urchins in different habitats, at different depths, and at different times of day on a fringing reef at Galeta Point, Panama. Algal transplants were then performed to determine the effect of herbivory on algal distribution and on potential plant-plant interactions in the absence of grazers. Thalassia loss on the reef flat (0%/h) and sand plain (0%/h) was very low relative to that on the shallow reef slope (14%/h). Within the reef slope habitat, herbivore activity decreased linearly with depth. On the shallow reef slope, herbivory was highest in habitats that were most topographically complex. Herbivory was reduced in microhabitats where algal turfs had decreased structural heterogeneity by overgrowing small branching corals and filling in the cavities that these corals normally provide. On the shallow reef slope, grazing of Thalassia was lowest at night (0.3%-1%/h), rose rapidly in the morning to peak between 0900-1300 h (27%-45%/h), then dropped gradually throughout the afternoon and returned to nocturnal rates at 1900-2000 h.Herbivorous fishes did 97% of their fedding during the daytime and were responsible for more than 90% of the Thalassia removed from the reef. Urchins accounted for only 9% of the Thalassia removal, and day and night grazing rates were not markedly different.Algal species from the reef flat and sand plain are excluded from the reef slope by herbivores, not physical parameters, and should outcompete reef-slope species in the absence of herbivory. On this tropical reef, plants in the more physically benign environment appear to be selected primarily for herbivore resistance. Selection for competitive ability among seaweeds becomes increasingly important in habitats where herbivores are more exposed to their own predators or where herbivore populations are low due to periodic physical disturbances.
在巴拿马加莱塔角的边缘礁上，利用泰来藻（Thalassia testudinum Banks ex König）的叶片进行了一项野外生物测定，以评估草食性鱼类和海胆在不同栖息地、不同深度以及一天中不同时间对其产生的影响。随后进行了藻类移植，以确定在没有食草动物的情况下，食草作用对藻类分布以及潜在的植物间相互作用的影响。相对于浅礁坡（14%/小时），礁坪（0%/小时）和砂质平原（0%/小时）上的泰来藻损失非常低。在礁坡栖息地内，食草动物的活动随深度呈线性下降。在浅礁坡上，地形最复杂的栖息地中食草作用最强。在一些微生境中，藻类草皮过度生长覆盖了小分支珊瑚并填充了这些珊瑚通常提供的洞穴，从而降低了结构异质性，食草作用也随之降低。在浅礁坡上，泰来藻的啃食率在夜间最低（0.3%-1%/小时），早晨迅速上升，在09:00-13:00之间达到峰值（27%-45%/小时），然后在整个下午逐渐下降，在19:00-20:00时恢复到夜间水平。草食性鱼类在白天完成了97%的摄食，并且导致从礁上移除的泰来藻超过90%。海胆仅占泰来藻移除量的9%，并且昼夜啃食率没有明显差异。来自礁坪和砂质平原的藻类物种是被食草动物排除在礁坡之外的，而非物理参数，并且如果没有食草动物，它们应该会在竞争中胜过礁坡物种。在这个热带礁上，处于物理环境更温和的环境中的植物似乎主要是因为对食草动物有抗性而被选择出来的。在食草动物更容易受到自身捕食者影响或者由于周期性物理干扰而食草动物数量较低的栖息地中，对海藻竞争能力的选择变得越来越重要。
