Marine Research Institute, University of Cape Town, Biological Sciences department, Cape Town, 7701, South Africa.
DST/NRF Research Chair in Shallow Water Ecosystems, Nelson Mandela Metropolitan University, Port Elizabeth, 6031, South Africa.
Sci Rep. 2016 Nov 17;6:37359. doi: 10.1038/srep37359.
Hippos transfer massive quantities of trophic resources from terrestrial to aquatic ecosystems through defecation. The ramifications of the latter for the functioning of benthic ecosystems are unknown, but are dependent ultimately on rates of utilisation relative to inputs. Low input and high utilisation can strengthen bottom-up pathways and enhance consumer biomass and abundance. However, if inputs exceed utilisation rates, dung can accumulate, leading to a decline in water quality, with important repercussions for resident assemblages. Here, we quantify the consequences of hippo dung inputs on benthic assemblages in an estuarine lake in South Africa. The system supports over a thousand hippos, and during recent drought periods (extending over a decade), hippo dung has been observed to form mats over benthic habitats. Enrichment of plots using exclusion/inclusion cages with dung at naturally occurring concentrations indicated a decline in benthic chl-a by roughly 50% and macrofaunal abundance, biomass and richness by up to 76, 56 and 27% respectively. Our findings suggest that persistent inputs of hippo dung can act as an important stressor of benthic systems, leading ultimately to a loss of productivity. Accumulation of hippo dung over benthic habitats is therefore an important mechanism by which hippos indirectly structure aquatic ecosystems.
河马通过排泄将大量营养资源从陆地生态系统转移到水生生态系统。后者对底栖生态系统功能的影响尚不清楚，但最终取决于利用率与输入率的关系。低输入和高利用率可以加强底栖途径，增加消费者生物量和丰度。然而，如果输入超过利用率，粪便就会堆积，导致水质下降，对当地生物群产生重要影响。在这里，我们量化了南非一个河口湖中河马粪便输入对底栖生物群的影响。该系统支持超过一千头河马，在最近的干旱时期（持续了十多年），人们观察到河马粪便在底栖生境上形成了垫子。利用含有自然浓度粪便的排除/纳入笼对斑块进行富集表明，底栖叶绿素 a 减少了约 50%，大型动物的丰度、生物量和丰富度分别减少了 76%、56%和 27%。我们的研究结果表明，河马粪便的持续输入可能是底栖系统的一个重要压力源，最终导致生产力丧失。因此，河马粪便在底栖生境上的积累是河马间接构建水生生态系统的一个重要机制。
