Effect of Seasonality and Associated Environmental Drivers on Macroinvertebrate Assemblages in Neotropical Coastal Headwater Streams

Comprehensive research into the environmental factors that affect the spatial and temporal variability of benthic macroinvertebrate communities in the headwater coastal streams of Ecuador is limited. Therefore, a study was carried out in four headwater coastal streams to address this gap. This study lasted for 2 years and included two surveys in summer and two in winter. The spatial and temporal variation of community metrics (abundance, richness, and diversity), functional feeding groups, and environmental factors were analyzed. A total of 47 genera from 33 families and 12 orders were collected, 29 of which were new records for the studied region. Seventy-nine percent of the total number of macroinvertebrates collected belonged to three orders of insects: hemipterans, ephemeropterans and coleopterans. The most abundant non-insect was the amphipod Hyalella. In seasonal terms, the populations of odonates, hemipterans, and coleopterans decreased in winter, whereas those of amphipods, trichopterans, ephemeropterans, and dipterans increased. The dominant functional feeding group consisted of predators, with the heteropterans Rhagovelia and Husseyella being the most abundant genera across all streams. Populations of predators and scrapers decreased in winter, whereas those of shredders and collectors increased. The results showed significant differences among the macroinvertebrate metrics obtained for each stream and season. The abiotic PCA ordination and biotic NMDS ordination of macroinvertebrate assemblages were consistent. The BEST routine inferred that the environmental variables that best explained assemblage patterns were phosphate concentration and stream width, although dissolved oxygen, water temperature, and current velocity were also important explanatory variables. In conclusion, seasons had a major influence on the macroinvertebrate assemblages of neotropical coastal headwater streams. During summer (the dry season), environmental stability supported higher richness and diversity, whereas in winter (the rainy season), hydrologic perturbation disrupted and altered the structure and composition of the macroinvertebrate community.