The River Continuum Concept provided a framework to predict the structure and function of fluvial ecosystems using habitat and energy parameters.  Subsequent work addressed landscape patchiness, conceiving of a “discontinuum” of alternating segments with differing characteristics and requiring more site-specific knowledge.  The Cape Horn Biosphere Reserve, Chile is part of the sub-Antarctic ecoregion, identified as one of the planet’s last 24 wilderness areas. This area has fallen outside of long-term research and monitoring efforts or global ecological analyses and environmental change studies.  We set out to fill this gap and provide baseline stream ecosystem information to better predict and monitor this biome by studying longitudinal habitat and biotic variations within a protected watershed, the Róbalo River, found in the Omora Ethnobotanical Park. This watershed contains an elevation transect from sea level to the highest mountains on the island (1,100 m) and also has a mosaic of the archipelago’s major habitats. We measured in-stream and riparian characteristics at 5 stations along the 33 km system at 100 m elevation intervals.  We quantified width, depth, velocity, bank slope, in-stream and riparian woody debris, bank cover substrate, benthic organic matter standing crop and macroinvertebrate assemblage.

Results/Conclusions

Generally, physical variables responded as expected. Width, depth, velocity and bank slope all significantly increased as elevation decreased, but not uniformly at all sites.  Basal resources were even more variable with no clear longitudinal trend, but vegetation zones were apparent with the density and composition of riparian tree seedlings varying from Nothofagus antarctica and N. pumilio co-dominance at higher elevation sites, followed by N. pumilio and N. betuloides co-dominance at mid-sites and lastly only N. betuloides near sea level.  Percent riparian herbaceous cover reflected similar patterns. Nonvascular plant cover decreased as elevation decreased, while woody debris significantly increased, as a consequence of greater forest cover.  Invertebrate composition varied strongly among stations and largely reflected riparian and in-stream conditions. Collector-gatherers abounded throughout the system, but proportionally decreased from 84% in headwaters to 28% at sea level, where filterers dominated (46%).  Shredders were infrequent throughout (≤1%), and only one large limnephilid caddisfly (Monocosmoecus hyadesi) was an important taxon in this group. Generally, the expectation that biotic communities respond to a habitat’s physical and energy parameters held true, but sub-Antarctic fluvial systems did not possess a predictable gradient of conditions from headwaters to mouth, largely due to landscape features that interrupt the continuum, such as lakes and beaver ponds.