Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Ecology & Evolutionary Biology
Non Technical Summary
The introduction of non-native species is one of the greatest threats to species diversity and ecosystem function throughout the world. Armored catfish, also known as plecos, are common in the aquarium trade, and have been released and become invasive in many sub-tropical and tropical freshwater ecosystems. High population densities of exotic armored catfish have been linked to declines in native fish populations and reductions in water quality. The researchers conducting this project hypothesize that through grazing, exotic armored catfish will alter nutrient cycling and primary productivity, decrease food quality and quantity for native grazing organisms, and reduce native biodiversity of macroinvertebrates and fishes in invaded systems. The investigators will study the impacts of armored catfishes on river systems in the Grijalva-Usumacinta watershed, a biologically and culturally diverse region in southern Mexico.
Animal Health Component
5%
Research Effort Categories
Basic
90%
Applied
5%
Developmental
5%
Goals / Objectives
Understanding the impacts of introduced vertebrates on community composition and ecosystem function is a critical step in predicting and mitigating the effects of introduced species in new environments. This study will elucidate the effects of an invasive grazing fish in invaded stream ecosystems and has three primary objectives. Initially, we will examine whether invasive loricariids are a quantitatively important phosphorus sink. Fish can be important P sinks in aquatic systems. We hypothesize that high population densities of armored catfish will selectively retain P and create a large, novel P-sink in invaded stream ecosystems. Secondly, we will assess the degree to which invasive loricariids modify basal resource quantity and quality and native species diversity and abundance. Grazers directly affect basal food resources through their feeding activities. They can reduce standing crops of epilithon via grazing. We posit that grazing by loricariids modify resource availability by reducing epilithon biomass and algal diversity. Moreover, we hypothesize that loricariids will alter epilithon stoichiometry by increasing the epilithon N to P ratio. Finally, we will determine the impact of an exotic grazer on primary productivity in an invaded system. High densities of grazing fishes can either enhance or depress primary productivity in freshwater systems. Fishes can decrease primary production by cropping algae and reducing the amount of bioavailable nutrients via nutrient sequestration. Conversely, aggregations of fishes can generate localized areas of rapid nutrient remineralization biogeochemical hotspots that increase primary productivity. To assess the effects of loricariid consumption and nutrient remineralization on primary productivity, we will test the following two alternative hypotheses: (1) primary productivity will decrease in response to loricariid grazing in invaded sites; and, (2) aggregations of loricariids will create biogeochemical hotspots that stimulate localized primary productivity relative to other areas in the stream.
Project Methods
We will utilize mesocosm and in situ experiments coupled with regional surveys to elucidate the effects of armored catfish on community structure and ecosystem processes in invaded rivers. We will use a nutrient-recycling approach to estimate the impact of loricariids on phosphorus (P) cycling in the Chacamax River. Nutrient recycling measurements express the rate at which nitrogen (N) and P are released in the environment by consumers. In a single invaded site, we will estimate the growth, ingestion, and nutrient recycling rates of loricariids. Ten additional loricariids will be collected and dissected and the C:N:P of the contents will be used to estimate nutrient assimilation. To estimate the effect of loricariid grazing on epilithon abundance, diversity, and stoichiometry, we will construct a series of enclosures and exclosures in one invaded site. We will create a randomized complete block design of five blocks and four treatments in one invaded site using 2m by 2m cages. Each experimental block will contain a fish exclosure, a fish enclosure, a cage control, and a reference plot. Cage controls will have the downstream side removed to allow access by the full fish assemblage. Scrubbed, flat rocks from the rivers will be placed within each treatment cage and will be sampled at 14 days and 28 days. We will also measure the primary productivity and algal diversity and abundance of epilithon on 10 rocks from three invaded and three uninvaded sites. At each site, we will measure primary productivity using in situ clear and dark chambers. We will also measure primary productivity in three additional invaded and three uninvaded sites described above. At each site, we will estimate primary productivity using three sets of light/dark chambers in three run microhabitats. Additionally, we will estimate the rate of nutrient remineralization and the size of the nutrient sink created by invasive loricariid populations. To assess the effects of excretion and egestion of loricariids on primary productivity in invaded systems, we will couple per capita excretion and fish density to predict how loricariid nutrient remineralization affects nutrient concentrations in an invaded system. We will collect paired samples of water chemistry within and outside aggregations of loricariids. Within aggregations will be defined as areas with greater than 25 fish per m2 and outside aggregations will be defined as locations with 0 fish per m2. Each sample site will be standardized for depth and flow. To estimate the effects of aggregations of loricariids on primary production, we will place six unglazed tiles in each of five sites within aggregations and five sites outside aggregations of armored catfish. Half of the tiles will be placed in cages to prevent loricariid grazing, but will allow ambient nutrients and nutrients excreted by loricariids to reach the tiles. Three tiles will remain unprotected from grazing. After 14 days of in situ incubation, we will estimate the primary productivity on the tiles to determine if additional nutrient inputs from armored catfish have localized positive effects on primary productivity.