Marine Sciences Program, Department of Biological Sciences, Florida International University, 3000 NE 151st Street, North Miami, Florida 33181, USA.
Ecology. 2013 Feb;94(2):530-6. doi: 10.1890/12-0705.1.
Biogeochemical hotspots can be driven by aggregations of animals, via excretion, that provide a concentrated source of limiting nutrients for primary producers. In a subtropical seagrass ecosystem, we characterized thresholds of ecological change associated with such hotspots surrounding artificial reef habitats. We deployed reefs of three sizes to aggregate fishes at different densities (and thus different levels of nutrient supply via excretion) and examined seagrass characteristics that reflect ecosystem processes. Responses varied as a function of reef size, with higher fish densities (on larger reefs) associated with more distinct ecological thresholds. For example, adjacent to larger reefs, the percentage of P content (%P) of seagrass (Thalassia testudinum) blades was significantly higher than background concentrations; fish densities on smaller reefs were insufficient to support sharp transitions in %P. Blade height was the only variable characterized by thresholds adjacent to smaller reefs, but lower fish densities (and hence, nutrient input) on smaller reefs were not sufficient for luxury nutrient storage by seagrass. Identifying such complexities in ecological thresholds is crucial for characterizing the extent to which biogeochemical hotspots may influence ecosystem function at a landscape scale.
生物地球化学热点可以由动物聚集驱动，通过排泄提供限制初级生产者生长的营养物质的集中来源。在亚热带海草生态系统中，我们描述了与人工礁石栖息地周围的这些热点相关的生态变化阈值。我们部署了三种大小的礁石，以聚集不同密度的鱼类（因此通过排泄提供不同水平的养分供应），并检查了反映生态系统过程的海草特征。响应随礁大小的变化而变化，较高的鱼类密度（在较大的礁上）与更明显的生态阈值相关。例如，在较大的礁石旁边，海草（塔希提测试顿姆）叶片的磷含量百分比（%P）明显高于背景浓度；较小礁石上的鱼类密度不足以支持 %P 的明显转变。叶片高度是唯一具有较小礁石边界特征的变量，但较小礁石上较低的鱼类密度（因此，养分输入）不足以支持海草的奢侈养分储存。确定生态阈值中的这种复杂性对于描述生物地球化学热点在景观尺度上可能影响生态系统功能的程度至关重要。
