Obligate groundwater crustaceans mediate biofilm interactions in a subsurface food web

Damiano Weitowitz, Anne Robertson, John Bloomfield, Louise Maurice, Julia Reiss

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Abstract

1. Groundwaters are an important resource for drinking water and groundwater communities contribute to the maintenance of this water quality via the breakdown of organic matter, nutrients and contaminants. In groundwater ecosystems, resource supply is scarce and food webs are dominated by few top-level consumers, mainly crustaceans. Many groundwater animals are only found here (stygobites), and thus groundwater communities also make a unique contribution to global biodiversity. These crustaceans clearly feed on groundwater biofilm, but it is uncertain if stygobites can control the abundance and composition of biofilm organisms.

2. We designed two microcosm experiments to explore the feeding effects of three stygobitic crustacean species on groundwater biofilms. Similar to surface waters, we predicted that the crustaceans would influence protozoan and bacterial abundances through grazing, while also changing their community structure. Firstly, we explored how the contrasting feeding behaviours of Niphargus fontanus and Proasellus cavaticus impacted upon groundwater biofilms over a four-day period. Secondly, we determined the direct and indirect effect of grazer (Niphargus kochianus) density on the protozoan and bacterial component of the biofilm. In this second experiment, biofilm responses were measured on nine occasions (bacteria) and six occasions (protozoa) over the course of 32 days.

3. We show that all three species of crustacean stygobites altered the biofilm, significantly increasing protozoan abundances compared to non-grazing controls. In the first experiment, the presence of Niphargus fontanus and Proasellus cavaticus significantly increased protozoan abundance. In the second experiment, with Niphargus kochianus, the high grazing density treatment also had significantly higher protozoan abundance and showed more protozoan morphotypes than the non-grazing control and the low grazing treatment. Bacterial densities were not affected by grazing at single time points, yet, when bacterial growth was followed over time, significantly different patterns were found between treatments without and with grazers. For example, medium-sized bacteria significantly increased in abundance over time compared to the control when grazer density (N. kochianus) was high.

4. Our controlled microcosm experiments are a rare demonstration that macroinvertebrate stygobites can influence and potentially regulate groundwater biofilm assemblages. Therefore, stygobites, through their influence on trophic elements in groundwater food webs, may modulate the denitrification and bioremediation services provided by aquifers and their associated ecosystems that contribute to the maintenance of this essential source of clean drinking water.

© 2019, North American Benthological Society. The attached document (embargoed until 24/07/2020) is an author produced version of a paper published in FRESHWATER SCIENCE uploaded in accordance with the publisher’s self- archiving policy. The final published version (version of record) is available online at the link. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.
Original languageEnglish
JournalFreshwater Science
DOIs
Publication statusPublished - 24 Jul 2019

Keywords

  • stygobites, protozoa, microcosms, bacteria, biofilm.

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