Functional responses of aquatic macroinvertebrates to flow regulation are shaped by natural flow intermittence in Mediterranean streams

Abstract

Running waters in Mediterranean regions are strongly regulated by dams, which produce significant alterations to natural flow regimes. Climate change will reduce discharge and increase flow intermittence in Mediterranean streams, which will lead to an intensified flow regulation to meet water demands. Very little is known about how the functional features of aquatic communities vary along combined anthropogenic flow alteration and natural intermittence gradients. As intermittent streams are subjected to natural stress (droughts and flash floods), the flow regime alteration effect may differ from that observed in perennial rivers. Consequently, studies that aim to determine the effects of flow regulation on the functioning of aquatic communities in a global change context are crucial. By applying linear mixed‐effect models and null models to the macroinvertebrate communities from 65 stream sites in the Segura River Basin (south‐east Spain), we assessed the separate effects of natural flow intermittence and flow regulation, as well as their interaction, on biological traits and functional diversity indices. Natural flow intermittence and flow regulation were mainly associated with loss of taxa with semivoltine or univoltine cycles and more sensitive aquatic stages (i.e. eggs), and with the replacement by taxa with multivoltine cycles and more resistant aquatic stages (i.e. adults). Flow regulation intensified the impact of natural flow intermittence on some biological traits, producing synergistic effects (i.e. decreasing interstitial taxa and tegument breathers and increasing taxa with aquatic adult stages). At the same time, antagonistic (life cycle) and opposing (shredders) interaction effects were also observed. Functional diversity, functional dispersion, and functional redundancy underwent a non‐random decrease as the flow regime alteration increased, and a significant antagonistic interaction was also found between both stressors for functional redundancy. In general, flow regulation effects were stronger in perennial than in intermittent streams because natural intermittence imposes a previous eco‐evolutionary pressure on aquatic biota by selecting those resistant or recovery traits that confer resilience to anthropogenic flow regime alterations. Thus, the natural flow regime influences the functional sensibility of communities to anthropogenic flow alteration.

Natural disturbances can produce misleading bioassessment results: Identifying metrics to detect anthropogenic impacts in intermittent rivers

“…Most of our new functional metrics responded differently at perennial and intermittent sites, as evidenced by antagonistic effects. Our results align with recent studies considering flow intermittence and salinity as natural disturbances combined with other anthropogenic impacts (Belmar et al, ; Gutiérrez‐Cánovas et al, ). The fact that intermittent rivers often showed a weaker reduction in functional metrics may reflect strong trait filtering in naturally disturbed ecosystems (Mouillot et al, ).…”

“…Functional metrics based on biological traits have shown to be promising tools for detecting anthropogenic impacts in different types of ecosystems (Laliberté et al, ; Mouillot, Graham, Villéger, Mason, & Bellwood, ; Statzner & Beche, ), and to be more accurate for the biomonitoring of naturally disturbed systems (Belmar et al, ; Bruno, Gutiérrez‐Cánovas, Velasco, & Sánchez‐Fernández, ). However, studies assessing the combined effects of natural disturbances and anthropogenic impacts on the functional composition of biological communities remain limited (e.g.…”

Taxonomic and Functional Responses of Benthic Macroinvertebrate Communities to Hydrological and Water Quality Variations in a Heavily Regulated River

“…The relevance of the functional approach has been already stressed in some biomonitoring indices (e.g., France, [35]) in which macroinvertebrate trait metrics are directly integrated. Moreover, functional redundancy has recently been proposed as a biomonitoring tool to monitor responses in the riparian vegetation [22] and tested on macroinvertebrate communities in a highly regulated Mediterranean basin [45].…”

Short-Term Responses of Aquatic and Terrestrial Biodiversity to Riparian Restoration Measures Designed to Control the Invasive Arundo donax L.

“…In particular, the riparian restorations took place in 52 km along the middle segment of the Segura River including the municipalities of Cieza, Calasparra and Moratalla (Murcia Region, Spain). This area is geologically characterized by the dominance of limestone, sandstone, gypsum and loam substrates and climatically featured by a mean annual precipitation of 300 mm and annual mean temperature of 17 • C. Regarding anthropogenic impacts, this perennial river reach is subjected to intense flow regulation and hydro-morphological alterations [52,53] mainly due to the upstream Cenajo reservoir, the biggest one (437 hm 3 ) in the Segura watershed. The main land use in the area is semi-natural (dominant shrubby landscape) and agriculture (mainly drylands, rice fields, apricot and peach trees), with urban areas being scarce (<2%; Figure 1).…”