Basins for Fish and Ecoregions for Macroinvertebrates: Different Spatial Scales Are Needed to Assess Louisiana Wadeable Streams

Abstract

We targeted wadeable streams in six USEPA Level III ecoregions spanning eight major study basins in northern Gulf of Mexico coastal plains and terraces to identify appropriate spatial frameworks for the assessment of stream quality, as well as fish species and macroinvertebrate families that were characteristic of least disturbed conditions. We analyzed previously collected (1990–2006) and recently collected (2005–2010) stream fish and macroinvertebrate data with mean similarity analysis to identify spatial frameworks, either basins or ecoregions, appropriate for the assessment of stream fish and macroinvertebrates. We also conducted partial redundancy analysis of fish and macroinvertebrates separately, controlling for differences in stream size, and variance partitioning to identify the variation attributable to ecoregion or basin as a measure of the importance of spatial influence. Our results indicated that fish distributions were better described by basins, with anticipated strong dissimilarities in fish community composition between river basins west and east of the Mississippi River. In addition, we found unexpected differences in Pearl River and Red River basin fish communities relative to neighboring study basins and unexpected similarities among the geographically distant fish communities in the Western Gulf Coastal Plain and Mississippi Alluvial Plain Ecoregions. Conversely, once we accounted for the expected dissimilarity caused by the Mississippi River, macroinvertebrate data were better explained by ecoregion than basin. Our analyses indicated that the incorporation of both spatial classifications for assessment will be necessary in this region.

Received September 8, 2011; accepted January 14, 2013

ACKNOWLEDGMENTS

The authors thank Phil Crocker of the United States Environmental Protection Agency, Emelise Cormier and Amanda Vincent of the Louisiana Department of Environmental Quality, Ross Hartfield formerly of the Louisiana Department of Environmental Quality, Charlie Demas and Scott Mize of the United States Geological Survey, David Byrd of the United States Department of Agriculture Forest Service, and the Louisiana Department of Wildlife and Fisheries. Field collections were conducted by Michael Campbell, Kayla (DiBenedetto) Kimmel, A. Raynie Harlan, Anne (Commagere) Hijuelos, Peter Markos, Adam Piehler, Mason Piehler, Aaron Podey, Chad Thomas, Brian Ward, Jonathan West, and Angela Williamson. Portions of this project were funded by the United States Environmental Protection Agency as Interagency Agreement # W-950518-01. This manuscript was improved by the comments of four anonymous reviewers. This manuscript was approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript 2012-241-6388.