Long-term studies of seasonal variability enable evaluation of macroinvertebrate response to an acute oil spill in an urban Mediterranean-climate stream

Abstract

Benthic macroinvertebrates show seasonal fluctuations with variability in hydrologic conditions. Coastal northern California (USA) is located in a Mediterranean-climate area, which is characterized by predictable wet and dry seasons, and consequently stream flows. Monthly sampling over multiple years (2004–2005, 2010–2013) was used to examine seasonal variability in taxonomic composition and abundances of benthic macroinvertebrates at three sites in Strawberry Creek, an urban stream on the University of California, Berkeley campus. Although wet and dry seasons at all sites had similar taxa occurrences, seasonal variation in taxa abundances was evident at two sites. The effects of an accidental oil spill in winter 2011 were examined using a Before–After design. Three days post-spill, macroinvertebrate richness and abundances at the impacted site decreased dramatically compared with pre-spill levels; taxonomic composition recovered one year later. Resilience was likely from drift via an unaffected stream fork and the flushing effects of winter stream flows. The combination of monthly sampling over multiple years and the opportunistic evaluation of responses to an acute disturbance enabled us to identify five taxa that are common, abundant, and easily identified, which can be used as a framework for enhancing future volunteer-based biomonitoring research projects.