Pine needle litter acts as habitat but not as food source for stream invertebrates

MÁRQUEZ, JAVIER A.; PRINCIPE, ROMINA E.; CIBILS MARTINA, LUCIANA; ALBARIÑO, RICARDO J.

INTERNATIONAL REVIEW OF HYDROBIOLOGY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2017

1434-2944

Small streams are ruled by the influence that riparian vegetation has on food webs since itregulates the entry of organic matter and sunlight. The plantation of perennial tree species alongbanks of grassland streams results in heavy shading of stream bottoms and large inputs of coarseorganic matter. In this study,weexperimentally analyzed the taxonomic and trophic structure ofinvertebrate assemblages colonizing pine needles and plastic filaments (mimicking the physicalstructure of needle accumulations) placed in one afforested and one natural grassland streamfrom the mountainous region of central Argentina. We studied these two experimentalsubstrates to infer if pine leaves were colonized by invertebrates as food resource or only as asubstratum for support and refuge. Coarse mesh litter bags were used to simulate large litteraccumulations and four bags of each treatment were randomly removed after 46, 89, and158 days of exposure. Our study showed that taxonomic and trophic composition ofinvertebrate assemblages colonizing needles and plastic filaments were mostly similarsuggesting that needles constitute mainly a stable habitat but not a trophic subsidy. Richness,diversity, and evenness were lower in assemblages of the afforested stream and differences intaxonomic and trophic structure were also found between afforested and natural grasslandstreams. We conclude that environmental changes associated to afforestation modifiedinvertebrate assemblages colonizing litter but in the same way for needles and plastic filamentssince no evidence was found for supporting that the organic nature of needles makes thissubstrate different from plastic filaments for invertebrates. Therefore, needles would not bebeing used as a food resource. Our study highlights the importance of preserving riparian zonesmostly unaltered to maintain natural aquatic communities when implementing afforestationprogrames in grassland landscapes.