Abstract
In this study, performed in Mediterranean brackish ponds during spring season, we assessed the effects of biotic interactions and abiotic factors on the size and taxonomic structure of the phytoplankton and zooplankton. We used a taxonomic and a size diversity index as a descriptor of the community structure. We predicted that the size diversity of each trophic level would be mainly related to biotic interactions, such as size-based fish predation (in the case of zooplankton) and food resource availability (in the case of phytoplankton), whereas taxonomic diversity would be more affected by abiotic variables (e.g., conductivity, pond morphology). Our results showed a negative relationship between phytoplankton size diversity and food resource availability leading to low size diversities under food scarcity due to dominance of small species. Conductivity also negatively affected the phytoplankton size diversity, although slightly. Regarding zooplankton size diversity, none of predictors tested seemed to influence this index. Similar fish size diversities among ponds may prevent a significant effect of fish predation on size diversity of zooplankton. As expected, taxonomic diversity of phytoplankton and zooplankton was related to abiotic variables (specifically pond morphometry) rather than biotic interactions, which are usually body size dependent, especially in these species-poor brackish environments.
Highlights
Mediterranean ponds are ecologically very important ecosystems that support relevant hydrological, chemical and biological processes and are biodiversity hotspots in terms of both species composition and biological traits [1]
While taxonomic diversity of zooplankton and macroinvertebrates communities was more sensitive to abiotic factors such as nutrient availability, size diversity was mainly related to biotic interactions [19,23]
In this study, performed in Mediterranean brackish ponds, we aimed to determine the effects of biotic interactions and abiotic factors on the phyto- and zooplankton taxonomic and size diversity indexes, and explore if they are affected by the same factors
Summary
Mediterranean ponds are ecologically very important ecosystems that support relevant hydrological, chemical and biological processes and are biodiversity hotspots in terms of both species composition and biological traits [1]. They are very vulnerable habitats, because they are threatened by several anthropogenic pressures [2,3]. Most ecological studies of Mediterranean ponds have been focused on their taxonomic diversity [2], the dynamics of a certain species and communities [6,7,8,9] and its relationship with nutrients dynamics and hydrological patterns [10,11,12,13], as well as with anthropogenic pressures [14]. Abiotic factors can affect the size structure of a community
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