How do substrate composition and environmental variables influence the richness and abundance of molluscs in an urban river from the Brazilian semiarid region?
Description
This study investigates the influence of substrate composition and environmental variables on the richness and abundance of freshwater molluscs in the urban stretch of the Guaribas River, located in the semi-arid region of Piauí, Brazil. Bimonthly collections were conducted between October 2021 and August 2022 across five sampling points, where molluscs were gathered from sediment and macrophyte substrates. Environmental parameters, including pH, water temperature, and water column depth, were also recorded. A total of 2479 individuals were identified, predominantly gastropods, with higher species richness and abundance observed in macrophyte substrates compared to sediment. Statistical analysis revealed a positive correlation between mollusc abundance and macrophyte presence and a significant interaction between pH and temperature on mollusc distribution. The results highlight the crucial role of macrophytes in enhancing habitat complexity and supporting mollusc diversity while demonstrating the negative impact of sediment pollutants in urban river systems. These findings provide insights into the ecological dynamics of molluscs in semi-arid environments, contributing to conservation and management strategies in these regions.
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Steps to reproduce
We conducted bimonthly collections between October 2021 and August 2022 along the urban stretch of the Guaribas River in the city of Picos in the semi-arid region of Piauí, Brazil. We established five sampling points, each at least 10 metres apart, and at each, we collected three samples of molluscs associated with sediment and those associated with macrophytes (Figure 1). For collecting molluscs associated with sediment, we used a metal sieve fixed to a wooden handle approximately 1.5 metres long, which was immersed five times down to the river sediment. The material was stored in labelled plastic containers with lids. To collect molluscs associated with macrophytes, we used a quadrat measuring 25 x 25 cm, which was randomly thrown once for each sample into the macrophyte beds. All the contents within the quadrat were removed and placed in labelled plastic bags. We recorded environmental parameters for each sediment and macrophyte sample, such as water temperature, pH, and water column depth. All the material collected was transported to the Biology Laboratory at the Federal Institute of Education, Science and Technology of Piauí (IFPI), Pico's campus, where we washed the macrophytes to remove attached molluscs and separated the molluscs from the river sediment. After separating the animals from the substrates, we distinguished live animals from dead ones and identified them using specialised literature and consultation with experts. To assess the influence of environmental variables on the structuring of the mollusc community, we selected species richness and abundance as response variables. These were analysed using generalised linear models (GLMs) fitted to the independent predictor variables pH, water temperature, substrate type (macrophyte or sediment), and water column depth. We evaluated the model fit using a mixed-effects negative binomial model due to the data distribution and the lack of independence among samples. To ensure uniform comparison, continuous predictors were standardised (mean = 0, standard deviation = 1) before analysis. All analyses were conducted in R Studio, using the glmer.nb function from the lme4 package (Bates et al. 2015), alongside the DHARMa (Hartig 2018), report (Makowski et al. 2023), psych (Revelle 2015), and MuMIn (Bartoń 2023) packages, which were used, respectively, to check model residuals, test results, correlations between variables, and pseudo-R² values for fixed effects.
Institutions
- Universidade Federal da Paraiba
- Instituto Federal de Educacao Ciencia e Tecnologia do Piaui - Campus Picos
- Universidade Federal do Piaui