The density and biomass of mesozooplankton and ichthyoplankton in the Negro and the Amazon Rivers during the rainy season: the ecological importance of the confluence boundary

PeerJ

article

Ryota Nakajima¹  Elvis V. Rimachi²  Edinaldo N. Santos-Silva²  Laura S.F. Calixto²  Rosseval G. Leite³  Adi Khen¹  Tetsuo Yamane⁴  Anthony I. Mazeroll⁵  Jomber C. Inuma⁷  Erika Y.K. Utumi⁸  Akira Tanaka⁸ 

[1] Scripps Institution of Oceanography, University of California San Diego;Plankton Laboratory, Biodiversity Coordination, National Institute of Amazonian Research;National Institute of Amazonian Research;Biotechnology Laboratory, Amazonas State University;Soka University of America;Amazon Research Center for Ornamental Fishes;Centro de Projetos e Estudos Ambientais do Amazonas;Instituto Água Floresta e Vida

关键词: River boundary;    Negro;    Solimões;    Aggregation;    Fish larvae;    Copepods;    Cladocerans;    Predation risk;    Amazon;    Neotropical;   

DOI  :  10.7717/peerj.3308

学科分类：社会科学、人文和艺术（综合）

来源: Inra

【 摘 要 】

The boundary zone between two different hydrological regimes is often a biologically enriched environment with distinct planktonic communities. In the center of the Amazon River basin, muddy white water of the Amazon River meets with black water of the Negro River, creating a conspicuous visible boundary spanning over 10 km along the Amazon River. Here, we tested the hypothesis that the confluence boundary between the white and black water rivers concentrates prey and is used as a feeding habitat for consumers by investigating the density, biomass and distribution of mesozooplankton and ichthyoplankton communities across the two rivers during the rainy season. Our results show that mean mesozooplankton density (2,730 inds. m−3) and biomass (4.8 mg m−3) were higher in the black-water river compared to the white-water river (959 inds. m−3; 2.4 mg m−3); however an exceptionally high mesozooplankton density was not observed in the confluence boundary. Nonetheless we found the highest density of ichthyoplankton in the confluence boundary (9.7 inds. m−3), being up to 9-fold higher than in adjacent rivers. The confluence between white and black waters is sandwiched by both environments with low (white water) and high (black water) zooplankton concentrations and by both environments with low (white water) and high (black water) predation pressures for fish larvae, and may function as a boundary layer that offers benefits of both high prey concentrations and low predation risk. This forms a plausible explanation for the high density of ichthyoplankton in the confluence zone of black and white water rivers.

【 授权许可】

CC BY