Abstract

River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages have been documented in several Andean river drainages. Coastal river drainages are comparatively small, but inordinately important because of their highly endemic flora and fauna and their proximity to major human populations. For conservation purposes it is important to understand what environmental factors affect assemblage structure of fishes especially in the comparatively high diversity coastal drainages. We studied patterns of fish distribution and abundance in three rivers of the coastal, Andalien drainage near Concepción, Chile. We used multi-dimensional scaling analyses to compare patterns among zones (rithron, transition and potamon) and high and low flow seasons. Species assemblages differed by zone, but not with season. Assemblages consisted of nested subsets of species characterized by their range of distribution among zones. One species group was composed of widespread species that occurred in all three zones, another species group consisted of species found only in transitional and potamal zones, and a final group was comprised of species found only in the potamal zone. The potamal zone contained the most diverse and abundant fish assemblage. Fish assemblages were related to both water quality and habitat structure variables. This study suggests that the key to conserving the diversity of native fish communities in coastal Chilean rivers is in the conservation of potamal regions. Unfortunately, most protected areas in Chile are in the depauperate headwaters of drainages. Protection of only headwaters is clearly inadequate and will not contribute to the conservation of this unique freshwater fish fauna.