Contribution of macroinvertebrate shredders and aquatic hyphomycetes to litter decomposition in remote insular streams

Abstract

Shredders play a crucial role in litter decomposition in streams. However, in oceanic islands, many streams have low shredder density and richness, and microbes seem to be the main litter decomposers. Here, we evaluate the effects of shredders and aquatic hyphomycetes on litter decomposition in insular streams. Three leaf species differing in physical and chemical characteristics, Alnus glutinosa, Clethra arborea, and Cryptomeria japonica, were enclosed in bags of coarse and fine mesh to allow and avoid macroinvertebrate access to the litter, respectively, and incubated in six streams along a gradient of Limnephilus atlanticus (Trichoptera) density in Sa ˜o Miguel Island. In streams with higher L. atlanticus density, leaf mass loss was higher in coarse than fine mesh bags. However, no difference in litter mass loss was found between bag types in streams with no L. atlanticus, despite the presence of other shredder taxa. These results suggest that when L. atlanticus are present at relatively high densities, they significantly contribute to litter decomposition, while litter decomposition is mainly driven by microbes when L. atlanticus density is low, or they are absent. Moreover, litter decomposition depends on litter quality, with leaves with high nutrient concentration and low concentration of secondary compounds being preferred by shredders.

Testing the Tea Bag Index as a potential indicator for assessing litter decomposition in aquatic ecosystems

“…It is The copyright holder for this preprint this version posted April 27, 2021. ; https://doi.org/10.1101/2021.04.26.441560 doi: bioRxiv preprint Litter decomposition is an important process in aquatic systems (Graça et al, 2015), playing a major role in the global cycling of carbon and nutrients (Battin et al, 2009;Gessner et al, 1999;Graça et al, 2015). Three main factors control aquatic litter decomposition: litter quality (Jabiol et al, 2019;Neiff et al, 2006); environmental factors such as temperature, nutrient availability, salinity, acidity, and oxygen concentration (Almeida Júnior et al, 2020;Ferreira et al, 2015;Gomes et al, 2018;Griffiths and Tiegs, 2016;Woodward et al, 2012;Young et al, 2008); and decomposer community composition, including macroinvertebrates, fungi, and bacteria (Balibrea et al, 2020;Hieber and Gessner, 2002).…”

Aquatic Hyphomycetes from streams on Madeira Island (Portugal)

“…Here we present the first study that explored the distribution of aquatic hyphomycetes in insular streams from Madeira Island. Twenty-one taxa are recorded for Madeira Island, which is lower than what is reported for the Azores archipelago (41 species; see Ferreira et al 2016b , Ferreira et al 2017 , Balibrea et al 2020 ). However, these numbers cannot be used to draw conclusions about aquatic hyphomycetes species richness in each archipelago since sampling has used different approaches and has been limited in both archipelagos: in Madeira, aquatic hyphomycetes were sampled on one occasion from water in a large number of streams spatially distributed to cover the entire island surface, while in the Azores, aquatic hyphomycetes have been sampled on multiple occasions from submerged litter in few streams in one of the nine islands (São Miguel) of the Archipelago.…”

“…The aquatic hyphomycete assemblages of Madeira were composed mainly by ascomycetes with a cosmopolitan distribution ( Duarte et al 2016a , Seena et al 2019 ) which are also known from other oceanic islands ( Ranzoni 1979 , Ferreira et al 2016b , Ferreira et al 2017 , Balibrea et al 2020 ). In fact, other studies ( Fenchel 1993 , Finlay and Clarke 1999 , Finlay 2002 , Finlay and Fenchel 2004 ) suggested the high capacity of dispersal of microorganisms with few geographical barriers when compared to macroorganisms, such as freshwater macroinvertebrates ( Hughes et al 1998 , Hughes and Malmqvist 2005 , Raposeiro et al 2012 ).…”

Global patterns and drivers of coniferous leaf-litter decomposition in streams and rivers

“…The lack of information on CLL decomposition in freshwaters is, therefore, unrealistic and may lead to biased results when investigating general patterns of LL decomposition in freshwaters on a global scale. In addition, CLL naturally differs from broadleaved LL in ways of leaf morphology, nutrient concentration (e.g., N and P), chemical (e.g., lignin) and physical (e.g., toughness) characteristics, and, especially, the nutritional quality, which is lower than broadleaved LL (Martínez et al, 2013;Balibrea et al, 2020). Leaf-litter traits refer to characteristics that have correlations with LL decomposability or palatability, which include nutrient concentrations and chemical and physical characteristics in this study.…”