Variability in stream macroinvertebrate community composition along climate and flow permanence gradients in California

Abstract

Temporary streams—one of the most common freshwater ecosystems—are natural habitats of great ecological and landscape interest. In the future, the proportion of temporary streams is expected to increase due to changes in the climate. It may produce abrupt variations in the ecosystem function and hence on their invertebrate community. This research project shows evidence of how climate change is currently impacting California, producing variations in the stream’s hydrology. In total, 7 temporary streams, mainly located in the East Bay of San Francisco area, have been sampled. The sampling took place during the months of January-May 2020 and the data obtained has been compared with previous research findings from several scientific papers. The main aim of this research project is to examine the variability in stream macroinvertebrate community composition along (1) a geographical-climatic gradient and (2) a flow permanence gradient in Central California. This way, we tried to identify which parameters from these mentioned gradients produce greater effects on the invertebrate communities inhabiting our sampled streams. The findings of this research allow us to make predictions about future responses to the product that climate change episodes are pouring on the lotic ecosystems. To develop our study, we compared multiple macroinvertebrate metrics and traits between 4 intermittent (long/medium-flow) and 2 ephemeral (short-flow) streams during the wet period and compared them with environmental variables. We found that macroinvertebrates were primarily influenced by three ecological gradients: (i) water temperature, (ii) canopy cover and (iii) channel slope. Macroinvertebrates in ephemeral rivers were mainly influenced by the first gradient, whereas in intermittent rivers the second and third gradients were more important. Additionally, ecological connectivity between nearby streams also played an important role among the variability observed in each site, either at environmental or taxonomic level. We conclude that the benthic macroinvertebrate richness and abundance in variable environments are mainly determined by hydrological variation and differences in local habitat factors. As climate change scenarios predict severe modification of hydrological and local habitat factors, this study suggests that in river management, hydrological restoration should be prioritized over other local habitat factors by maintaining its natural hydrological variability and so avoid unregular changes. It would ensure aquatic community richness and diversity.