A trait‐based framework for stream algal communities

Abstract

The use of trait‐based approaches to detect effects of land use and climate change on terrestrial plant and aquatic phytoplankton communities is increasing, but such a framework is still needed for benthic stream algae. Here we present a conceptual framework of morphological, physiological, behavioural and life‐history traits relating to resource acquisition and resistance to disturbance. We tested this approach by assessing the relationships between multiple anthropogenic stressors and algal traits at 43 stream sites. Our “natural experiment” was conducted along gradients of agricultural land‐use intensity (0–95% of the catchment in high‐producing pasture) and hydrological alteration (0–92% streamflow reduction resulting from water abstraction for irrigation) as well as related physicochemical variables (total nitrogen concentration and deposited fine sediment). Strategic choice of study sites meant that agricultural intensity and hydrological alteration were uncorrelated. We studied the relationships of seven traits (with 23 trait categories) to our environmental predictor variables using general linear models and an information‐theoretic model‐selection approach. Life form, nitrogen fixation and spore formation were key traits that showed the strongest relationships with environmental stressors. Overall, FI (farming intensity) exerted stronger effects on algal communities than hydrological alteration. The large‐bodied, non‐attached, filamentous algae that dominated under high farming intensities have limited dispersal abilities but may cope with unfavourable conditions through the formation of spores. Antagonistic interactions between FI and flow reduction were observed for some trait variables, whereas no interactions occurred for nitrogen concentration and fine sediment. Our conceptual framework was well supported by tests of ten specific hypotheses predicting effects of resource supply and disturbance on algal traits. Our study also shows that investigating a fairly comprehensive set of traits can help shed light on the drivers of algal community composition in situations where multiple stressors are operating. Further, to understand non‐linear and non‐additive effects of such drivers, communities need to be studied along multiple gradients of natural variation or anthropogenic stressors.

Modelling diatom life forms and ecological guilds for river biomonitoring

“…An approach based on ecological guilds and life forms is suitable to disentangle the interactions of multiple stressors and understand how nutrients, water flow and substrates shape diatom communities (Lange et al, 2015). The results of this study could help industrials and environmental managers to identify and quantify which specific chemical and physical alterations are caused by a polluted effluent in a river.…”

Effects of intensive agriculture in the structure and functioning of tropical headwater streams

“…These results are in agreement with the Stream Biome Gradient Concept, which hypothesizes that stream biological features changes predictably along climate characteristics (DODDS et al, 2015). Interestingly and supporting our hypothesis, nitrate concentrations did not demonstrate effects on diatom functional diversity, as commonly observed in temperate streams (BIGGS;CLOSE, 1989;PASSY, 2007;LANGE et al, 2015). Because of highly dynamic environmental variability in headwater streams, linked with the high-intensity storms that are commonly observed in tropical regions, climate characteristics modulate benthic diatom community in tropical headwater streams.…”

“…Agricultural land use and flow regimes are the main factors affecting resource supply, organic matter, energy cycling and physicochemical habitat characteristics in streams (LANGE et al, 2015). The conversion of forests to agricultural landscapes shifts the surface runoff and stream discharge, increasing erosion, sediment loads and leaches nutrients and agricultural chemicals to streams .…”

“…Agricultural effects on tropical streams have been investigated and changes in fish TERESA et al, 2015), macroinvertebrate (BENSTEAD;DOUGLAS;PRINGLE, 2003;LORION;KENNEDY, 2009; and microbial (BOECHAT et al, 2011) To evaluate the anthropogenic effects on streams, benthic biofilm has been used in temperate systems in biomonitoring programs. In these systems, predictable changes can be observed following shifts in nutrient availability and flow dynamics (PASSY, 2007;BERTHON et al, 2011;LANGE et al, 2015), allowing the conception of a trait-based framework for stream algal communities to detect effects of land-use and climate change (LANGE et al, 2015). Indices and frameworks developed for temperate systems are often applied to tropical streams, due to lack of information on ecological preferences and tolerances of benthic diatoms (BERE, 2015), and consequences for applied issues are likely.…”

“…Traitbased approaches can refine our mechanistic understanding of biological communities in a taxon-independent manner, allowing the comparison across ecosystems and transforming descriptive into predictive studies in community ecology (VERBERK et al, 2013;SCHMERA et al, 2015). For benthic diatoms, traits are classified according to the resistance to physical disturbance, nutrient enrichment, and life forms, in genus-level taxonomic resolution (PASSY, 2007;BERTHON et al, 2011;SCHNECK;MELO, 2012;LANGE et al, 2015). The use of coarse taxonomic resolution in genus-level has been applied in tropical river floodplains, with similar responses to environmental variation as species-level (RIBAS; PADIAL, 2015).…”