Spatial variations at different observational scales and the seasonal distributions of stream macroalgae in a Brazilian subtropical region

Abstract

-(Spatial variations at different observational scales and the seasonal distributions of stream macroalgae in a Brazilian subtropical region). We examined the relationships between environmental variations in lotic ecosystems with the seasonal dynamics of macroalgae communities at different spatial scales: drainage basin of two rivers (Rio das Pedras and Rio Marrecas), shading (open and shaded stream segments), mesohabitat (riffles and pools), and microhabitats. Data collections were made on a monthly basis between January and December/2007. A total of 16 taxa were encountered (13 species and 3 vegetative groups). All of the biotic parameters (richness, abundance, diversity, equitability, and dominance) were found to be highly variable at all of the spatial scales evaluated. On the other hand, abiotic variables demonstrated differences only at mesohabitat (in terms of current velocity) and shaded habitat (in terms of irradiance) scales. The seasonality of the macroalgae community structure was strongly influenced by microhabitat variables (current velocity, substrate H', and irradiance), demonstrating their importance over time and at different scales. Regional variables (temperature, oxygen saturation, specific conductance, pH, and turbidity) were found to have little influence on the temporal dynamics of the macroalgae communities evaluated.

Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river

“…Comparable results were reported in a number of streams in the Brazilian subtropical region (Krupek et al, 2012). Indeed, a large body of evidence points to the highly positive effect exerted by spatial heterogeneity on species diversity: an increase in substrate diversity is expected to enhance the niche and resource availability needed to support a wide range of taxa (Murdock and Dodds, 2007;Krupek et al, 2012). In addition, data collected in riparian river sectors largely fed by groundwater have shown that groundwater resurgence exerts a highly positive effect on local plant diversity, which may be ascribed to higher soil pH and higher nitrogen availability (manifested as a lower soil C/N ratio) (Kuglerová et al, 2014).…”

“…By contrast, the RHI sites, along with the GWD sites, exhibited the highest degree of diversity and cover values. Their heterogeneous hard substrate (micro-, mesolithal; Table 1) and general stream-like characteristics support these results (Sheath et al, 1986;Krupek et al, 2012). However, both the POT and RHI stretch types were characterized by a relatively low number of algal taxa.…”

“…This additional source of water supply substantially increases the riverbed microhabitat complexity and may explain the marked algae diversity. Comparable results were reported in a number of streams in the Brazilian subtropical region (Krupek et al, 2012). Indeed, a large body of evidence points to the highly positive effect exerted by spatial heterogeneity on species diversity: an increase in substrate diversity is expected to enhance the niche and resource availability needed to support a wide range of taxa (Murdock and Dodds, 2007;Krupek et al, 2012).…”

“…in-river structures, serial discontinuities) on macrophyte diversity and distribution emerge as the most critical aspects when evaluating primary producer dynamics in rivers (Werner and Köhler, 2005;Krupek et al, 2012;Cattaneo et al, 2013). Following the river continuum concept (Vannote et al, 1980) and the serial discontinuity concept proposed by Ward and Stanford (1983), a large body of literature has outlined the contribution of river fragmentation to fish population dynamics and population viability as well as to macroinvertebrate community patterns (Guareschi et al, 2014;Peacock et al, 2016).…”

“…Information of this kind is not yet available for the non-vascular and non-diatomic components of riverine primary producers (Kelly and Whitton, 1998), and few studies have investigated the seasonal dynamics of soft-bodied benthic algae (Sheath and Burkholder, 1985;Necchi Júnior et al, 1991, 1995Branco and Necchi Júnior, 1997;Krupek et al, 2012).…”