2023 Early Hearing Detection & Intervention Conference

March 5-7, 2023 • Cincinnati, OH

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6/08/2017 | 10:15 AM - 10:30 AM | SHADE AND GRAZING, NOT PHOSPHORUS, LIMIT ALGAL BIOMASS IN TROPICAL BRAZILIAN ATLANTIC FOREST (MG) STREAMS. | 306B

SHADE AND GRAZING, NOT PHOSPHORUS, LIMIT ALGAL BIOMASS IN TROPICAL BRAZILIAN ATLANTIC FOREST (MG) STREAMS.

We manipulated nutrients grazers and predators in enclosures implanted in a shaded and a partially open site in an Atlantic Brazilian forest stream to address the question of whether these streams are top-down limited by grazers or bottom-up limited by light and nutrients. Algal biomass was low (56 to 162 µg chl-a /m ²). A 58% increase in light resulted in 2.2 fold increase in algal biomass (128 vs. 343 µg chl-a /m ²) and 4 fould increase in primary production (from 10 to 40 mg C m ² day ^-1). Nutrient (P) addition did not stimulate algal standing crop. Helicopsyche grazing caused a 49 to 59% algal biomass reduction when compared with treatments with no grazers. The presence of Anacroneuria sp. (predator) did not reduce feeding by Helicopsyche. Substrates exposed to shade and semi-open sites differed in the dominance of some algal taxa. We conclude that (1) shade and herbivory control algal biomass and in these Atlantic forest streams; and (2) small changes in the light entering the streams can have profound implications in primary producers.

C22 Disturbance
S09 The importance of environmental gradients for the advance of tropical stream ecology
C25 Food Webs

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Presenters/Authors

Manuel Graça (), MARE, University of Coimbra, Portugal , mgraca@ci.uc.pt;