Sub-Antarctic streams break the rules: functional feeding groups along watershed gradients with and without urban impact

Abstract

The River Continuum Concept (RCC) has been widely used to understand the relationship between abiotic conditions, basal resources and aquatic communities, including longitudinal patterns of benthic macroinvertebrate functional feeding groups (FFG). However, the RCC has been quested for southern hemisphere temperate streams, and we asked whether it applies to sub-Antarctic streams in southern Patagonia. We studied FFG assemblages in Fuegian stream gradients with urbanization and reference conditions (?type?). We assessed physicochemical characteristics and basal resources in 6 streams (54°50' S, 68° W). We measured FFG abundance with 4-5 benthic samples using a Surber net (450 um mesh) in each watershed?s upper, mid and lower reaches (N = 85). We conducted ANOVAs and perMANOVAs to evaluate differences due to stream type and reach on the proportion of each FFG and overall FFG assemblage, respectively. Urban streams had lower canopy cover, dissolved oxygen, and substrate size and higher temperature and nutrient concentration, compared to Reference streams. The overall assemblage differed among stream reaches and type. While RCC hypothesized higher proportion of shredders in headwaters, scraper in mid-, and collector-filterers in lower-waters, In Reference reaches, shredders were more abundant in midstream, and no differences were found for the other FFGs between reaches In Urban streams, collectors-gatherers were more abundant downstream; scrapers increased towards midstream, decreasing downstream, and collector-filterers had the greatest abundance upstream. Moreover, shredders were more abundant in Urban streams, and collector-filterers in Ref streams. FFG distribution in Fuegian streams differed from the expectations of the RCC, which relies on gradients in basal resources. This might be due to extreme upstream conditions (e.g., low temperature and nutrient concentrations). Moreover, although collector-gatherers had similar proportion comparing downstream areas between RCC and Urban streams, it might be consequence of the availability of resources (RCC) and their tolerance to urban conditions (unexpected in RCC).