Abstract
AbstractHarmful algal blooms (HABs) are globally increasing in number and spatial extent. However, their propagation dynamics along environmental gradients and the associated interplay of abiotic factors and biotic interactions are still poorly understood. In this study, a nutrient gradient was established in a linear meta‐ecosystem setup of five interconnected flasks containing an artificially assembled phytoplankton community. The harmful dinoflagellate Alexandrium catenella was introduced into different positions along the nutrient gradient to investigate dispersal and spatial community dynamics. Overall, total algal biovolume increased, while community evenness decreased with increasing nutrient concentrations along the gradient. Alexandrium was able to disperse through all flasks. On the regional scale, diatoms dominated the community, whereas on the local scale the dinoflagellate showed higher contributions at low nutrient concentrations and dominated the community at the lowest nutrient concentration, but only when initiated into this flask. A control treatment without dispersal revealed an even stronger dominance of Alexandrium at the lowest nutrient concentration, indicating that dispersal and the associated nutrient exchange may weaken dinoflagellate dominance under low nutrient conditions. This study presents a first approach to experimentally investigate spatial dynamics and ecological interactions of a harmful dinoflagellate along an environmental gradient in a meta‐ecosystem setup, which has the potential to substantially enhance our understanding of the relevance of dispersal for HAB formation and propagation in combination with local environmental factors.
Highlights
S3, S8, S10), supporting the first part of hypothesis H1 stating a biovolume increase along the gradient of increasing nutrients. This pattern supported the effectiveness of our nutrient gradient until the end of the experiment, which could not be substantiated by nutrient data
The setup we used proved to be suitable for investigating ecological interactions and Harmful algal blooms (HABs) dynamics along an environmental gradient, along which inoculation position, dispersal, and the local nutrient regime determined the population dynamics of our target species Al. catenella
Only one dispersal regime was tested in this study, and it is conceivable that the relevance of inoculation position diminishes with increasing dispersal rate
Summary
Diatoms often bloom during or shortly after upwelling events in nutrient-rich waters when mixing is high, while dinoflagellates dominate after nutrient depletion and stabilization of the water column, that is, when mixing decreases and stratification increases (Langlois and Smith 2001; Kudela et al 2005; Anderson et al 2008). Such temporal successions from diatoms to dinoflagellates, which are tightly coupled to hydrography and nutrient dynamics, are commonly. Alexandrium spp. have been shown to feed mixotrophically (Jeong et al 2010) and to be able to store nutrients (Collos et al 2004), potentially promoting their dominance especially under nutrient-depleted conditions (see earlier)
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