Drought and community dynamics of macroinvertebrates in Mediterranean climate intermittent streams of California

Although most streams in California are intermittent, bioassessment protocols are designed for perennial streams, with sampling periods anytime between April and June. Sampling intermittent streams during this period may not provide an accurate assessment of stream health, because of the stream community dynamics related to the predictable drying of intermittent streams in Mediterranean climates. Furthermore, climate change may cause perennial streams to become intermittent and intermittent streams to cease flow entirely. The objectives of this study were to assess the recolonization process and community dynamics within and among three intermittent streams each with a different hydrologic regime (dry, isolated pools, and low flow in the summer/fall months) and to assess whether the current bioassessment protocol sampling period appropriately accounts for differences in community composition recovery of intermittent streams. Macroinvertebrates and environmental information were collected at three intermittent streams from August 2013 to July 2014 near Sunol, CA. Sampling was conducted at frequent intervals (1, 8, 15, and 22 days) once stream flow resumed after the dry season; after 22 days, samples were collected every three weeks until the streams dried. All streams exhibited rapid recolonization (especially San Antonio Creek, which only flowed for five weeks) once flow resumed, suggesting taxa were well adapted to the Mediterranean climate and may have resistant/resilient life history traits to survive drying in the summer months. Taxa richness was highest in isolated pool habitats (due to an increase in x_x000D_ predatory and air breathing taxa), contradicting most findings that increased connectivity is associated with higher taxa richness. Non Metric Multidimensional Scaling was used to assess community composition within and among the three streams. Communities became more similar during months of continuous flow (February, March, and early April), suggesting that an earlier sampling window than currently used would be useful for bioassessment. In conclusion, there is a need for more studies regarding macroinvertebrate community dynamics in relation to standard bioassessment sampling protocols and how the effects of floods, flow permanence, and drought influence community dynamics in Mediterranean climate intermittent streams.