Fish communities critically depend on forest subsidies in small neotropical streams with high biodiversity value

• Published in: Biotropica 2021-07, Vol.53 (4), p.1096-1108
• Main Authors: Roussel, Jean‐Marc, Covain, Raphael, Vigouroux, Regis, Allard, Luc, Treguier, Anne, Papa, Yvan, Le Bail, Pierre‐Yves
• Format: Article
• Language: English
• Subjects: Algae; Ancistrus; Biodiversity; Biodiversity and Ecology; Canopies; Canopy; Carbon; Carbon sources; Dry season; Environmental Sciences; Exploitation; Fins; Fish; Food chains; Food webs; forest streams; French Guiana; freshwater fish; headwater streams; Headwaters; Herbivores; Isotope ratios; Isotopes; Lignocellulose; Marine fishes; molecular phylogeny; Muscles; Nitrogen; Organic carbon; Phylogeny; Piscivores; Prey; Ratios; Rivers; Seabirds; Solar radiation; Species; Stable isotopes; Streams; Subsidies; Terrestrial environments; terrestrial subsidies; terrestrial‐aquatic linkage; Tropical climate; Tropical fish; Tropical fishes; Tropical forests
• ISSN: 0006-3606; 1744-7429
• DOI: 10.1111/btp.12949

Trophic support of species‐rich tropical fish communities remains uncertain in small forest streams where dense and constant canopy cover strongly limits the solar radiation available to aquatic producers. We sampled >1300 fish from 80 species in 14 remote headwater streams during the dry season in French Guiana. Carbon and nitrogen stable isotope analyses and mixing models were run to estimate the trophic position (TP) of each species and its dependence on terrestrial organic carbon sources. Matching patterns were found between nitrogen stable isotope ratios and the literature on diets of species at the base and top of the food web. Nearly 60% of the species fed exclusively on animal prey (mean TP >3), including piscivorous and parasitic fish species. Phylogenetic analysis revealed that TP were distributed broadly along the phylogeny and changed gradually within lineages. Carbon stable isotope ratios differed strongly between herbivores that fed on aquatic primary producers and those that fed on terrestrial plants along banksides. Terrestrial carbon was dominant in nearly 90% of species, and most of them depended more or less exclusively on terrestrial carbon. Ancestral state reconstructions indicated that only a few lineages showed local changes toward the consumption of algal carbon. We conclude that fish in neotropical headwater streams shaded by a dense tree canopy depend strongly on terrestrial subsidies. Changes in this aquatic‐terrestrial linkage would have major consequences for the remarkable fish biodiversity in these streams. in French is available with online material. FRENCH ABSTRACT La contribution majoritaire du carbone algal aux réseaux trophiques d'eau douce a été démontrée, même dans la partie amont des bassins versants où les apports de carbone terrestre sont substantiels. Ces apports terrestres proviennent principalement de lignocellulose, une source de nourriture que les consommateurs n'assimilent pas bien sous les climats tempérés, contrairement aux algues de haute qualité nutritive. La prédominance de l'apport algal reste en questionnement dans les petits cours d'eau en forêt tropicale, qui diffèrent entre autre par un couvert forestier dense et constant limitant fortement le rayonnement solaire disponible pour les producteurs aquatiques, par les essences végétales elles même, et par les caractéristiques physicochimiques du sol et de l'eau. Nous avons étudié l'écologie trophique de 80 espèces de poissons (> 1300 individus) issues de