Replicability of physicochemistry and macroinvertebrate assemblages in stream mesocosms: implications for experimental research

Abstract

1. The replicability of mesocosms is assessed in a case study of artificial streams (4 m 2 ) flanking a lowland chalk river in southern U.K. Among-mesocosm comparisons of physicochemistry and macroinvertebrate assemblage composition (in drift and benthos) were made during a 2-year survey of 12 outdoor once-through linear channels. 2. Mesocosm physicochemistry was highly replicable, with statistically significant congruence in temporal variation across the mesocosm series, low spatial variation and no significant blocking or positional effects arising from mesocosm layout. Parallel physicochemistry was attributed to the outdoor stream-side location and short water residence times. 3. Mesocosms were colonized by 127 macroinvertebrate taxa from 15 taxonomic orders. Both benthic and drifting assemblages were comparable among mesocosms, with no significant effect of mesocosm layout. Small differences in taxonomic composition were, however, evident among particular mesocosms, with higher (e.g. Tinodes, Limnius and Elmis) or lower (e.g. Pisidium and Valvata) abundances observed for a minority (5%) of taxa. We conclude that large (4 m 2 ) outdoor flow -through mesocosms can be replicable when located near to the source system and allowed to establish naturally.

Extreme Climatic Events Alter Aquatic Food Webs

“…This proof copy is the copyright property of the publisher and is confidential until formal publication. The limitations and potential shortcomings of the mesocosm approach that need to be borne in mind are mostly related to the logistical constraints that mean they are restricted to limited spatiotemporal scales and levels of biological complexity (Harris et al, 2007;Ledger et al, 2009;Stewart et al, 2013). Although the ability to replicate treatments is a clear advantage of mesocosms, their ecological realism to whole freshwater systems has also been questioned (Petersen and Englund, 1995;Schindler, 1998).…”

“…Whilst the mesocosms did not have extensive hyporheic zones, conditions were consistent with that observed in many headwater streams, where the majority of macrofauna are confined to surface sediments and shallow oxygenated interstices (Trimmer et al, 2010), and substrata provided physical refugia for suitably adapted species during drying disturbances (Harris, 2006). Physicochemical conditions were highly congruent among the mesocosms (Table 1; Harris et al, 2007 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter SPi. It is not allowed to publish this proof online or in print.…”

“…of particle sizes, 85% 11-25 mm, 5% 2-11 mm, 5% 0.35-2 mm, 5% < 0.35 mm), matching the source stream (Harris et al, 2007). Whilst the mesocosms did not have extensive hyporheic zones, conditions were consistent with that observed in many headwater streams, where the majority of macrofauna are confined to surface sediments and shallow oxygenated interstices (Trimmer et al, 2010), and substrata provided physical refugia for suitably adapted species during drying disturbances (Harris, 2006).…”

Climate change and freshwater ecosystems: impacts across multiple levels of organization

“…A recent study subjected a suite of replicated experimental stream channels to different intensities of drought designed to mimic the likely effects of patch scale dewatering resulting from the reduced flows and increased abstraction predicted for the coming decades (Harris et al 2007). The channel flows were diverted from an adjacent stream, to ensure a common source of water and potential colonists, and each one was divided into three sections that were then assigned to the experimental treatments (unmanipulated controls, three-monthly dewatering and monthly dewatering).…”

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…18). These model systems reflected the abiotic conditions, biodiversity and food web properties of natural streams Harris et al, 2007;Ledger et al, 2009). The results of this fragmentation experiment revealed some dramatic impacts on the food webs: consistent with the higher trophic rank hypothesis (e.g.…”