Spatiotemporal dynamics of basal food web resources and diatom and macroinvertebrate communities in a subtropical stream

Abstract

Seasonal changes in biotic communities and basal food web resources, including algae and organic matter, have been well studied in temperate environments but less so in subtropical streams. We assessed spatiotemporal variation in algal biomass, measured as ash-free dry mass (AFDM) and chlorophyll-a, coarse (CPOM) and fine (FPOM) particulate organic matter, macroinvertebrate communities, and diatom communities in a subtropical stream in south-central Texas over three years at multiple habitat types. Linear mixed models revealed seasonality significantly influenced AFDM, chlorophyll-a, CPOM, and FPOM. Canonical correspondence analysis revealed strong seasonal changes in diatom but not macroinvertebrate communities. Seasonal patterns generally matched those of temperate latitudes but with altered timing, including algal biomass peaks in winter as opposed to spring and CPOM peaks in spring as opposed to fall. Leaf loss and regrowth and seasonal hydrologic variability likely caused seasonal patterns, similar to mechanisms in temperate streams. Within seasons, physical habitat influenced patch-scale biomass of algae and organic matter, and macroinvertebrate communities showed stronger responses to physical habitat than seasonality. Although seasonal changes of basal food web resources were similar to patterns in temperate streams, differences in timing and across biotic communities may influence food web structure and function in subtropical streams.