Interdisciplinary research in the fields of ecohydrology and ecogeomorphology is becoming increasingly important as a way to understand how biological and physical processes interact with each other in river systems. The objectives of the current study were 1) to determine changes in invertebrate community due to hydrological stages, 2) to link local physical features [flow configuration, sediment composition and morphological feature) with the ecological structure between and within dissimilar morphological units (meander and confluence), and 3) to determine the existence and the origin of bed hydro‐geomorphic patches, determining their ecological structure. Results were discussed in the frame of prevailing ecological models and concepts. The study site extends over a floodplain area of the large Paraná River (Argentina), including minor and major secondary channels as well as the main channel. Overall results suggested that hydrodynamics was the driving force determining distribution patterns of benthic assemblages in the floodplain. However, while the invertebrates living in minor secondary channels seem to benefit from flooding, this hydrological phase had the opposite effect on organisms from the main and major secondary channels. We also found a clear linkage between physical features and invertebrate ecology, which caused a dissimilar fauna structure between and within the meander and the confluence. Furthermore, several sandy‐patches were recorded in the confluence. These patches were colonized by the particular benthic assemblage recorded in the main channel, supported the view of rivers as patchy discontinua, under uncertain ecological equilibrium.
The emergence and evolution of the heteromorphic life history in algae has been considered as a response to the selective pressures of changing environments. The brown alga Leathesia marina has a typical heteromorphic life history, alternating between microscopic branched filaments (gametophytic phase) and a macroscopic erect stage (sporophytic phase). The first aim of this study was to describe vegetative and reproductive morphologies of sporophytes (macrothalli and diploid phase) of L. marina and their relationship with environmental factors in an annual cycle. The second aim was to report the discovery of gametophytes (microthalli and haploid phase) in the natural environment on northern Patagonian coasts, and to describe their morphology, abundance and reproductive output. The macroscopic phase was observed over 8 months, from September to April during the warm season. The microscopic phase was observed in two periods, March-April and September-October. A temporal overlap was observed between the microscopic and macroscopic phases. The population of macrothalli had a type III survivorship curve. The cover, density and size of macrothalli were associated with warmer months, but the abundance of microthalli and reproductive output of both phases were higher in temperate periods. Demographic parameters, including mortality rate, survivorship, reproductive output and the morphological characteristics of L. marina are used to evaluate the adaptation of this species to a changing environment, typical of the temperate coasts of northern Patagonia in Argentina.
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