ABSTRACT: Caribbean coral reefs are experiencing a shift to algal dominance at the expense of stony corals. Determining the factors leading to algal phase shifts is crucial for assuring the survival of Caribbean coral reefs. In this study, factors controlling the growth of the abundant brown macroalgae Dictyota spp. were investigated by varying herbivory pressure (caging) and nutrients (fertilizer addition) on coral reefs near St. Thomas (US Virgin Islands). Experiment 1 measured Dictyota heights and percent cover at 3 sites (11-20 m depth) and showed no growth response to nutrient addition and a weak negative response to herbivory. To confirm results of Experiment 1, a caging and nutrient manipulation (Experiment 2) was conducted at one site (14 m depth) using the dependent variable Dictyota biomass. A strong negative response of growth to nutrient addition was shown, presumably because of nutrient inhibition, and an equally negative response to herbivory (loss of ~50% biomass over 21 d). The inhibitory effect of fertilization on growth was confirmed in a third experiment that showed increasing biomass loss over 4 treatment levels of increasing fertilizer addition (0 [ambient], 5, 10, 20 g). Overall, Dictyota was not nutrient limited at any sites, and was weakly controlled by herbivore populations. Factors responsible for Dictyota abundance on Caribbean reefs may reflect decreased herbivory caused by overfishing and reductions in coral cover and do not appear to be affected by recent changes in nitrogen or phosphorus load. This study reinforces the need for conservation and management of herbivores in coral reef ecosystems, to mitigate the effects from anthropogenic stressors.

中文翻译：

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升高的营养物质和食草动物对 Dictyota 的生长动态产生负面影响

摘要：加勒比珊瑚礁正在经历以石珊瑚为代价的向藻类优势的转变。确定导致藻类相移的因素对于确保加勒比珊瑚礁的生存至关重要。在这项研究中，控制丰富的棕色大型藻类Dictyota spp生长的因素。通过对圣托马斯（美属维尔京群岛）附近珊瑚礁的不同食草压力（笼养）和营养物质（添加肥料）进行调查。实验 1 测量了 3 个地点（11-20 m 深度）的dictyota高度和覆盖百分比，显示对营养添加没有生长反应，对食草动物有微弱的负面反应。为了确认实验 1 的结果，使用因变量在一个地点（14 m 深）进行了笼养和养分操作（实验 2）网店生物量。显示出生长对养分添加的强烈负面反应，大概是因为养分抑制，以及对食草动物的同样负面反应（21 天后生物量损失约 50%）。施肥对生长的抑制作用在第三个实验中得到证实，该实验表明，在增加肥料添加量（0 [环境]、5、10、20 克）的 4 个处理水平上，生物量损失增加。总体而言，Dictyota在任何地点都不受营养限制，并且受到食草动物种群的微弱控制。导致Dictyota 的因素加勒比珊瑚礁的丰度可能反映了过度捕捞和珊瑚覆盖减少造成的食草动物减少，并且似乎不受近期氮或磷负荷变化的影响。这项研究强调了保护和管理珊瑚礁生态系统中食草动物的必要性，以减轻人为压力源的影响。