Invasive Fishes Generate Biogeochemical Hotspots in a Nutrient-Limited System

Abstract

Fishes can play important functional roles in the nutrient dynamics of freshwater systems. Aggregating fishes have the potential to generate areas of increased biogeochemical activity, or hotspots, in streams and rivers. Many of the studies documenting the functional role of fishes in nutrient dynamics have focused on native fish species; however, introduced fishes may restructure nutrient storage and cycling freshwater systems as they can attain high population densities in novel environments. The purpose of this study was to examine the impact of a non-native catfish (Loricariidae: Pterygoplichthys) on nitrogen and phosphorus remineralization and estimate whether large aggregations of these fish generate measurable biogeochemical hotspots within nutrient-limited ecosystems. Loricariids formed large aggregations during daylight hours and dispersed throughout the stream during evening hours to graze benthic habitats. Excretion rates of phosphorus were twice as great during nighttime hours when fishes were actively feeding; however, there was no diel pattern in nitrogen excretion rates. Our results indicate that spatially heterogeneous aggregations of loricariids can significantly elevate dissolved nutrient concentrations via excretion relative to ambient nitrogen and phosphorus concentrations during daylight hours, creating biogeochemical hotspots and potentially altering nutrient dynamics in invaded systems.

Phosphorus body content in an herbivorous fish in environments with different trophic state

“…Other species within the family (Ancistrus triradiatus and Chaetostoma milesi) have been reported to show body P values of approximately 4.5% (Hood et al, 2005), while the Mexican invasive sailfin catfish Pterygoplichthys sp. presented an average P value of 5.7% (Capps and Flecker, 2013). Our results are in agreement with those found for some of these Loricari- idae species, although some fishes from the mesotrophic site presented body P values of less than 2%.…”

“…Differences in the organismal stoichiometry of populations from sites with different trophic status can lead to variations in the fish excretion rates, thus potentially affecting their role as nutrient recyclers. In disturbed sites, the ecological function of the species can change, with potential implications for the functioning of the ecosystem (Capps and Flecker, 2013;Spooner et al, 2013). Future studies should investigate if the trophic status of the environment has a direct or indirect effect on the fish body stoichiometry, to pin point the mechanisms generating the observed differences.…”

“…For fishes, besides nucleic acids that contain significant amount of P, bones and scales are also rich in this element (Vrede et al, 2004;Hendrixson et al, 2007). Loricariids, a common Neotropical fish family, are covered with armor-like bony plates, which lead to high body P concentrations (4-6%; McIntyre and Flecker, 2010), and therefore high P demand (Capps and Flecker, 2013). In environments with low P availability, loricariids can thus be P-limited (Hood et al, 2005;Capps and Flecker, 2013), even maintaining nutrient homeostasis.…”

“…Loricariids, a common Neotropical fish family, are covered with armor-like bony plates, which lead to high body P concentrations (4-6%; McIntyre and Flecker, 2010), and therefore high P demand (Capps and Flecker, 2013). In environments with low P availability, loricariids can thus be P-limited (Hood et al, 2005;Capps and Flecker, 2013), even maintaining nutrient homeostasis. The role of loricariids in the ecosystem as P sources of sinks can thus depend on their body elemental content and on the nutrient concentrations in the environment.…”

Sustaining Freshwater Biodiversity in the Anthropocene

“…This last 'idiosyncratic hypothesis' holds that the identity of species lost may be more crucial than the number remaining, and there is some evidence that this relationship applies in freshwater ecosystems (e.g. McIntyre et al 2007;Gessner et al 2010;Capps and Flecker 2013). Recent findings (e.g., Cardinale 2011;Cardinale et al 2012), and uncertainty over the form of the relationships between biodiversity and ecosystem functioning (see Dudgeon 2011;Tomimatsu et al 2013), strongly suggest that it would be prudent to adopt the precautionary principle and minimize further species declines or losses.…”