Severe and prolonged droughts in Caribbean tropical streams reached historically low records in minimal flow during the years 2014-2015 as consequence of the El Nino. Changes in water flow, a reduction in pool volume and habitats resulted in changes in the macroinvertebrates communities in headwater streams of Puerto Rico. Will these changes influence food webs if these relatively rare events become more frequent?
Decreases in rainfall and discharge caused a decreased in water velocity, pool depth, and changes the thermal regime and water chemistry. The absence of flows and the lack of connectivity among headwater pools during the drought resulted in changes in water chemistry. Streams showed enhanced diel fluctuation in dissolved oxygen at low flow near to the point of hypoxia. The macroinvertebrate abundance was affect by the long prolonged dry periods. The richness and abundance on insects increased during the drought and decreased and the end of the dry period. The abundance of the freshwater filter (Atya lanipes) and shredder (Xiphocaris elongata) shrimp decreased as the volume of the pools decreased. In contrast, the numbers of predators (Macrobrachium) increased during this period. Invertebrate abundance increased after low flow periods. These differences in predator and prey abundance are likely to change food-web structure if drought frequency increases. Some new species may disperse from intermittent streams into the previously perennial headwaters