Project Results

Background/Question/Methods

Rainbow trout (Oncorhynchus mykiss) have been repeatedly introduced into Ecuadorian streams since the 1920’s. The introduction of non-native trout can have profound effects on stream communities by means of nutrient enrichment and also by competing with native taxa. However, how non-native trout affect stream microbial communities and their associated function is largely unknown. To address this issue, we examined the association of the stream bacterial community structure with organic matter decay (function) and environmental variables among stream sites with (Trout) and without trout farms (NoTrout). We deployed cotton strips at 5 Trout stream sites and 5 NoTrout sites (20-29 day incubation). Bacterial communities were collected from cotton strips via standardized swabbing upon strip retrieval. We assessed bacterial community composition with Illumina™ (MiSeq) sequencing of the 16s rRNA gene region (V4) of bacterial DNA. Organic matter decay was assessed as percent loss of cotton strip tensile strength per degree day and utilized as a measure of stream bacterial community function. We compared bacterial community alpha diversity (richness and inverse Simpson index) and beta diversity between Trout and NoTrout stream sites. We used non-metric multidimensional scaling (NMDS) to explore bacterial community structure as related to environmental variables and organic matter decay.

Results/Conclusions

NMDS ordination displayed a pattern along NMDS axis 1 indicating a difference in bacterial community composition related to trout farming between sites. Furthermore, stream characteristics that are often altered by trout farming were correlated with NMDS axis 1 (pH: r = 0.69, p < 0.001; total dissolved solids: r = 0.59, p < 0.001; dissolved oxygen: r = 0.48, p = 0.004; and percent canopy cover: r = 0.83, p < 0.001). However, the rate of organic matter decay was not correlated with the NMDS. Bacterial taxonomic richness and diversity did not differ between Trout and NoTrout sites and the pattern observed in the NMDS ordination was not supported by permutation-based analysis of variance which indicated no significant effect of trout farming on bacterial community structure. Further research utilizing additional sites is needed to determine if and to what extent trout farming affects stream-associated bacterial community composition and function.

About This Project

Introduced rainbow trout can have profound effects on the chemical and biological characteristics of temperate streams including increased nutrients and species extirpation. How these non-native fish impact the unique cloud forest streams of Ecuador is unknown. We will examine the effect of trout on water chemistry, macroinvertebrate communities, and functional processes of several cloud forest streams to better inform management and evaluate and prevent possible degradation.

Ask the Scientists

What is the context of this research?

Rainbow trout (Oncorhynchus mykiss) were introduced into Ecuador in the 1920’s and the 1960’s (Crawford and Muir 2008). Even today, the Ecuadorian government is encouraging rainbow trout hatchery programs (Vimos et al. 2015, MAGAP 2016). Trout farms can have a detrimental effect on streams and their biota through the release of pathogenic bacteria, chemicals/antibiotics, and nutrient enrichment from trout excrement and food wastes (Stewart et al. 2006). Furthermore, non-native trout can have repercussions throughout the stream ecosystem by altering the food web from algae to fishes (Baxter et al. 2004, Vimos et al. 2015) and even disrupting the forest ecosystem through reduction in terrestrial invertebrates and amphibian species (Gillespie 2001, Baxter et al. 2004).

What is the significance of this project?

With the growth of the human population and increasing global change, streams throughout the world are suffering. The need to understand how stream ecosystems respond to our influence is desperately needed now, so that we can respond with educated management decisions before habitat and biotic loss is unrecoverable. The urgency of this research is even more prevalent in the species-rich Ecuadorian cloud forests. This research will help us to understand the role introduced rainbow trout play in ecology of mountain streams of Ecuador. In addition, this research will support and be coupled with research exploring the effects of introduced trout on disease susceptibility, abundance, and distribution of glass frogs, a species that are rapidly disappearing throughout the Neotropics.

What are the goals of the project?

We will be quantifying and comparing the chemical, physical, and biological condition of a minimum of 5 stream reaches above and below rainbow trout farms in the cloud forests of Ecuador. At each site we will collect water samples for chemical analysis and macroinvertebrates for community analyses. In addition, we will be measuring organic matter decay by deploying cotton strips and then analyzing them for loss in tensile strength (Tiegs et al. 2013). Funds from this grant will go towards the cost of collecting and analyzing the samples. In addition, the knowledge gained through this study will be used in a parallel study that is exploring the abundance and distribution of glass frogs and their susceptibility to disease.