Environmental factors – spatial and temporal variation of chironomid communities in oceanic island streams (Azores archipelago)

¹ Research Center in Biodiversity and Genetic Resources (CIBIO) – Açores, and Biology Department, University of Azores, Rua Mãe de Deus 13A, 9501-855 Ponta Delgada, Açores, Portugal
² Centre for the Research and Technology of Agro-Environment and Biological Sciences, University of Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal

^* Corresponding author: raposeiro@uac.pt

Received: 9 February 2011
Accepted: 15 June 2011

Abstract

Freshwater systems on volcanic oceanic islands have very particular characteristics as a result of their geological origins, relatively small size, distances from source areas for colonizers, and distinct catchment morphology. These factors result in freshwater communities that are clearly distinct from continental systems. Chironomid spatial and temporal distribution was investigated in chironomid assemblages at 21 sites across the Azores Archipelago. Results using PERMANOVA, a permutational multivariate analysis of variance, indicated significant longitudinal differences in assemblages but none between islands or over time.

Links between hydromorphological and physicochemical variables and the community assemblage were assessed using DISTLM, a linear model for distance-based multivariate analysis. The percentage of variation explained by hydromorphological factors (31%) was slightly higher than that explained by physicochemical (28%) factors. Descriptors of land use (forest area, scrub area, natural area of catchment) and stream slope were found to be the best environmental predictors of chironomid assemblages in Azores. Physicochemical variables such as temperature, pH, nitrite, iron and conductivity were the principal drivers of change in chironomid composition in stream locations. Headwater sites, characterized by lower temperature, acid to neutral pH values, low conductivity, nutrient and metal concentrations were dominated by Rheocricotopus atripes. Mid-section sites, located in agricultural areas were dominated by Thienemanniella clavicornis. Urbanized lower reaches were characterized by higher temperature, pH, conductivity and nutrient levels and were dominated by Cricotopus sp. These results give essential information that allows us to predict the response of different chironomid species to hydromorphological and physicochemical gradients across the archipelago's streams contributing providing the basis for the development of tools for the implementation of the Water Frame Directive.