TY - JOUR TI - When the rainforest dries: Drought effects on a montane tropical stream ecosystem in Puerto Rico AU - Gutiérrez-Fonseca, Pablo E. AU - Ramírez, Alonso AU - Pringle, Catherine M. AU - Torres, Pedro J. AU - McDowell, William H. AU - Covich, Alan AU - Crowl, Todd AU - Pérez-Reyes, Omar T2 - Freshwater Science AB - Global climate change predictions include decreased precipitation and more frequent droughts in many world regions. In the aseasonal wet tropics, predicting potential impacts is particularly challenging because droughts are rare and therefore poorly understood. In 2015, the Caribbean islands experienced the most severe drought within the past 5 decades. Here, we use this extreme event as an opportunity to assess how tropical stream ecosystems draining the Luquillo Experimental Forest (LEF) in Puerto Rico respond to severe drought. During 2015, precipitation was 45% lower than the long-term (1975–2016) average for the LEF, resulting in a 54% reduction in stream discharge. After 5 mo of declining discharge (April–August 2015), one branch of our focal study stream system became a series of isolated pools and a few riffle-type runs, while the other branch had greatly reduced flow between its pools. Concentrated biotic activity within pools resulted in elevated and highly-variable nutrient (5.1–12.1 µg PO43−-P/L; 12.9–57.2 µg NH4+-N/L; 80.0–160.0 µg NO3−-N/L) and specific conductance (95–114 µS/cm) levels among pools. However, the algal standing crop was 14× lower than the previous 15-y average despite increases in nutrient levels, reflecting intense grazing pressure of insect and shrimp consumers, potentially due to decreased pool volume. Higher nutrient levels in stream pools did increase biofilm productivity, and at the peak of the drought daily fluctuations in dissolved oxygen ranged from ∼1.0 to 6.5 mg/L. Significantly-higher riparian inputs of organic matter (7.6× the long-term average) occurred during a 15-d period in May. The drought caused a general increase in macroinvertebrate density, with collector–gatherers and some grazer taxa increasing significantly at the peak of the drought, but taxonomic richness did not change. Omnivorous shrimp abundance increased slightly in response to decreased stream flow in one branch of our focal stream. Our study highlights the marked effects of severe droughts on neotropical streams in the wet tropics, with large effects on basal resources and consequent changes in trophic dynamics. Ultimately, our findings underline the need for a whole-ecosystem perspective to understand how streams respond to increased frequencies of extreme events associated with climate change. DA - 2020/06/01/ PY - 2020 DO - 10.1086/708808 DP - journals.uchicago.edu (Atypon) VL - 39 IS - 2 SP - 197 EP - 212 SN - 2161-9549 ST - When the rainforest dries UR - https://www.journals.uchicago.edu/doi/full/10.1086/708808 Y2 - 2021/08/31/13:30:45 KW - aseasonality KW - disturbances KW - low flow KW - neotropical streams KW - precipitation ER -