Ecohydrological costs and benefits of common carp, the dominant species in a ‘novel' tropical lake ecosystem

'Novel ecosystem' is a concept which was introduced in the 21st Century to describe ecosystems heavily modified by humans, about 15 years after 'ecohydrology' had been introduced as concept within UNESCO IHP, to facilitate the sustainable management of aquatic ecosystems by humans and about 5 years after the concept of IHP 'Demonstration Sites' had been introduced to promote ecohydrological principles globally. The tropical African Lake Naivasha became a DS initially to demonstrate the importance of papyrus-dominated wetland edges for nutrient and climate control in an aquatic ecosystem driven by regional hydrological instability, but it already represented a ‘novel’ ecosystem. This paper critically examines the consequences of the aquatic food web restructuring by the major alien species, common carp (Cyprinus carpio L.) – whose arrival is directly an ecological consequence of hydrological instability. Carp were first recorded in Lake Naivasha in 2001 and reached dominance in the commercial fishery by 2003. The costs and benefits of its dominance are shown by comparing aspects of the ecosystem state before and after arrival. These were hypothesized and tested by comparing data in 2012-4 with data gathered in the 1990s using the same methodologies. Carp have filled a previously vacant benthivorous niche. The species achieved moderate density but has not caused ecological disruption. Overall, carp has been a positive contributor to the local community. More intensive management strategies, better post-harvest processing and new marketing techniques need to be developed to enhance financial gain

Freshwater phytoplankton diversity: models, drivers and implications for ecosystem properties

Our understanding on phytoplankton diversity has largely been progressing since the publication of Hutchinson on the paradox of the plankton. In this paper, we summarise some major steps in phytoplankton ecology in the context of mechanisms underlying phytoplankton diversity. Here, we provide a framework for phytoplankton community assembly and an overview of measures on taxonomic and functional diversity. We show how ecological theories on species competition together with modelling approaches and laboratory experiments helped understand species coexistence and maintenance of diversity in phytoplankton. The non-equilibrium nature of phytoplankton and the role of disturbances in shaping diversity are also discussed. Furthermore, we discuss the role of water body size, productivity of habitats and temperature on phytoplankton species richness, and how diversity may affect the functioning of lake ecosystems. At last, we give an insight into molecular tools that have emerged in the last decades and argue how it has broadened our perspective on microbial diversity. Besides historical backgrounds, some critical comments have also been mad