6/07/2017  |   09:00 - 09:15   |  306B

UNDERSTANDING TROPICAL STREAM RESPONSES TO URBANIZATION: THE CASE OF THE RIO PIEDRAS WATERSHED IN PUERTO RICO Our understanding of tropical urban streams is limited. Puerto Rico offers a unique opportunity to study tropical urban streams. We have been focusing on the Rio Piedras, the main watershed draining the San Juan Metropolitan Area of Puerto Rico, with the goal of understanding stream responses to urban gradients. Our goal is to understand how urbanization is affecting the various components of stream ecosystems in Puerto Rico and how they change over time. Along a gradient of increasing urbanization, our studies indicate that water chemistry shows the expected increase in ion concentrations and a decrease in insect diversity. Fish and shrimp are not strongly affected by urbanization and are present in most reaches with appropriate habitat. However, fish assemblages are changing in response to hydrological changes and drought. Leaf litter decomposition decreases with increasing urbanization and riparian food webs also show negative impacts. Our finding highlight the importance of hydrology and habitat availability for maintaining ecosystem function. Overall, urban streams in Puerto Rico are a good model for understanding how streams in tropical coastal areas respond to urbanization once major sewage discharges are removed.

Alonso Ramírez (Primary Presenter/Author), North Carolina State University, alonso.ramirez@ncsu.edu;


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6/07/2017  |   09:15 - 09:30   |  306B

When the rainforest dries up: Impacts of severe drought in a tropical stream Precipitation is never constant in rainforests and annual fluctuations are often large. While extremely low precipitation (drought) occurs infrequently, it can act as a major disturbance in stream ecosystems. Understanding the effects of droughts is critical, as tropical areas are expected to progressively receive less precipitation due to climate change. In this study, we use our long-term data set (2009-2015) to assess the impacts of a severe drought during 2015 upon a third-order stream draining the El Yunque National Forest, Puerto Rico. In 2015, rainfall was 44.6% lower than the average annual precipitation. Discharge declined and physicochemical parameters were variable and related to changes in stream flow. Leaf-litter fall increased by 35% compared to our long-term data. Macroinvertebrate abundance was 10 times higher than the long-term average, but there was no change in taxonomic richness. Finally, organic biofilm (AFDM) increased and chlorophyll-a decreased. Our study highlights the dramatic effects of drought on tropical streams, with potentially large repercussions on ecosystem processes. This underlines the need for long-term data to understand how stream ecosystems respond to extreme events and climate change.

Pablo E. Gutiérrez-Fonseca (Primary Presenter/Author), University of Costa Rica, pabloe.gutierrezfonseca@gmail.com;


Alonso Ramírez ( Co-Presenter/Co-Author), North Carolina State University, alonso.ramirez@ncsu.edu;


Catherine Pringle ( Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, cpringle@uga.edu;


Pedro J Torres ( Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, torresp@denison.edu;


Alan Covich ( Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, a.covich@gmail.com;


Todd Crowl ( Co-Presenter/Co-Author), Florida International University, facrowl@gmail.com;


William H McDowell ( Co-Presenter/Co-Author), University of New Hampshire, bill.mcdowell@unh.edu;


Omar Perez-Reyes ( Co-Presenter/Co-Author), University of Puerto Rico- Rio Piedras, macrobrachium@gmail.com;


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6/07/2017  |   09:30 - 09:45   |  306B

Effects of macroconsumers on benthic communities, primary productivity, and sediment dynamics in tropical karst streams with varying degrees of riparian cover Trophic cascades in streams manifest through addition or loss of consumers. Few have addressed experimentally the effects of land use on macroconsumers as well the consequences of consumer loss on trophic interactions. We sought to investigate how trophic cascades induced by macroconsumers interact with land use change in karst streams of southwestern Brazil. Macroconsumers were experimentally excluded from benthic habitats in streams that varied in the extent of riparian forest cover to determine how exclusion affected benthic invertebrates and periphyton. Macroconsumer exclusion resulted in suppressed chlorophyll-a concentrations and reduced biodiversity in assemblages of primary producers. We detected no treatment effect on periphyton dry mass and benthic invertebrates. Most parameters did not change along a gradient of riparian vegetation cover, suggesting that the effects of land use change in these hydrologically complex watersheds may not be strong enough strong effects. Trophic interactions associated with the behavior of invertebrate grazers could have contributed to the patterns that we observed. Some groups associated with karstic biogenesis may have responded to the absence of predators by constructing retreats more freely, a finding supported by subsequent detection of elevated CaCO3 deposition in treatment replicates.

Ryan Utz ( Co-Presenter/Co-Author), Chatham University, utz.ryan@gmail.com;


Elaine Corrêa (Primary Presenter/Author), Universidade Federal de Mato Grosso do Sul, elaineccorrea@yahoo.com.br;


Fabio de Oliveira Roque ( Co-Presenter/Co-Author), Universidade Federal de Mato Grosso do Sul, roque.eco@gmail.com;


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6/07/2017  |   09:45 - 10:00   |  306B

FOOD WEBS, COMMUNITY ASSEMBLAGES, AND ORGANISMAL STOICHIOMETRY ALONG ENVIRONMENTAL GRADIENTS IN TWO MESOAMERICAN RIVER NETWORKS The Grijalva-Usumacinta watershed is a center of freshwater biodiversity and endemism in southern Mexico. Our objectives were to survey aquatic assemblages, examine feeding ecology of fishes, and investigate patterns in fish tissue stoichiometry in two large Mesoamerican rivers--the Grijalva and the Usumacinta. The rivers are subject to different types and intensities of development and drain diverse terrestrial ecosystems. Additionally, the Usumacinta is currently undammed, while the Grijalva has several large impoundments. We compared habitats in the main-stem rivers and in smaller tributaries. We observed remarkable fish diversity in the Usumacinta basin, whereas fish diversity was lower in reaches of the Grijalva basin. Furthermore, stable isotope analysis revealed fish production in the main stem of the Río Usumacinta was supported by a broader variety of food resources compared to the Río Grijalva. We did not document striking patterns in organismal stoichiometry in fishes with broad distributions in either river. Our results suggest the natural flow regime in the Usumacinta promoted resource diversity by maintaining habitat heterogeneity and providing connectivity to riparian forests and the natural flow regime of the Usumacinta supports the diversity and value of fisheries in the river.

Krista Capps (Primary Presenter/Author), University of Georgia, kcapps@uga.edu;
Research in Krista Capps's lab is dedicated to understanding how anthropogenic activities alter community structure and ecosystem processes (e.g., productivity, decomposition, and biogeochemical cycling) in freshwater ecosystems. Much of her research has focused on the impacts of consumers on basal food resources, community structure, and nutrient dynamics in streams and wetlands. To translate scientific knowledge to actionable outcomes, she actively works with community groups and local, state, and federal employees to develop programs that integrate stakeholder concerns into research planning.

Allison Pease ( Co-Presenter/Co-Author), Texas Tech University, allison.pease@ttu.edu ;


Maria Mercedes Castillo ( Co-Presenter/Co-Author), El Colegio de la Frontera Sur, Villahermosa, mmcastillo@ecosur.mx ;


Manuel Mendoza-Carranza ( Co-Presenter/Co-Author), El Colegio de la Frontera Sur, Villahermosa, xoof1@yahoo.com ;


Rocío Rodiles-Hernández ( Co-Presenter/Co-Author), El Colegio de la Frontera Sur, San Cristóbal de las Casas, rrodiles@ecosur.mx;


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6/07/2017  |   10:00 - 10:15   |  306B

PHOTOSYNTHESIS, RESPIRATION AND NITROGEN UPTAKE CHARACTERISTICS OF STREAM SUBSTRATA IN TROPICAL STREAMS: HETEROGENEITY AND SCALING Leaves, epilithon, macrophytes and fine benthic organic material are central to food webs and nutrient fluxes in streams. However, most estimates of gross primary production (GPP) and ecosystem respiration (ER) are taken at a reach-scale, omitting information on how these different compartments contribute to frame whole-stream estimates. We measured substrate-specific GPP and ER and ammonium and nitrate 15N uptake in recirculating chambers, to evaluate autotrophic and heterotrophic contribution to metabolic characteristics. We compared these decimeter-scale measurements to whole-stream estimates concurrently measured in three sites across a river continuum in a preserved Atlantic forest in Brazil. Epilithon and macrophytes (when present) were the dominant GPP and N uptake compartments in open canopy sites, but leaves contributed strongly to ER even though they covered a small percentage of the stream bottom. Ammonium and nitrate uptake was significantly different between substrata and streams with different canopy cover. However, up-scaled results showed that total nitrogen uptake was only different when macrophytes were present and whole-stream uptake estimates were consistent with chambers estimates for ammonium but not for nitrate in the smallest closed canopy stream.

Flavia Tromboni (Primary Presenter/Author), University of Nevada, Reno, ftromboni@unr.edu;


Walter Dodds ( Co-Presenter/Co-Author), Kansas State University, wkdodds@ksu.edu;


Vinicius Neres-Lima ( Co-Presenter/Co-Author), Universidade do Estado do Rio de Janeiro, vinicius.lima.eco@gmail.com;


Eugenia Zandona ( Co-Presenter/Co-Author), Universidade do Estado do Rio de Janeiro, eugenia.zandona@gmail.com;


Timothy P. Moulton ( Co-Presenter/Co-Author), Universidade do Estado do Rio de Janeiro, moulton.timothy@gmail.com;


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6/07/2017  |   10:15 - 10:30   |  306B

INTRODUCED ONCHORYNCHUS MYKISS ALTER INSTREAM NUTRIENT CYCLING IN THE NAPO RIVER BASIN, ECUADOR Astroblepus a genus of catfish (order Siluriformes) and the sole genus of the family Astroblepidae, were historically abundant in highland streams throughout the tropical Andes up to elevations of 3500m. However, since the introduction of rainbow trout (Onchorynchus mykiss) into the region, Astroblepus have been displaced to lower elevations and are rarely found in sympatry with rainbow trout. Beyond the direct effect of displacing Astroblepus, rainbow trout introductions in the tropical highlands also indirectly affect ecosystem function through altered nutrient storage and cycling. We examined the influence of introduced rainbow trout populations on nutrient storage and cycling relative to native Astroblepus vaillanti populations along an elevational gradient (2500m-1000m) in the Napo River Basin of Ecuador. Our preliminary results indicate that rainbow trout populations contribute a significantly higher nitrogen subsidy relative to Astroblepus populations through excretion, indicating potential alteration of instream nitrogen cycling. We did not find a significant difference for soluble reactive phosphorus subsidies between the two populations.

Alexander Alexiades (Primary Presenter/Author), Heritage University, alexiades_a@heritage.edu;


Andrea C. Encalada ( Co-Presenter/Co-Author), Instituto BIOSFERA, Universidad San Francisco de Quito, Cumbayá, Ecuador Biológicas y Ambientales, Universidad San Francisco de Quito, Cumbaya, Ecuador, aencalada@usfq.edu.ec;


Alexander Flecker ( Co-Presenter/Co-Author), Cornell University, Ithaca, NY, USA, asf3@cornell.edu;


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