Assessment of anthropogenic influences on littoral-zone aquatic communities of Lake Texoma, Oklahoma-Texas, USA

From 1999-2001, we evaluated the effects of anthropogenic activities in and around Lake Texoma, Oklahoma-Texas, USA, on the structure of littoral-zone fish and benthic invertebrate assemblages at 20 potentially impacted sites relative to paired reference sites. Spatial structuring of both assemblages was strongly related to variables associated with water clarity, water-column chlorophyll-a levels, and degree of site exposure to wind and waves. Fish assemblages at reference sites and impact sites exhibited minor differences, but none that were considered indicative of severe anthropogenic stress. Conversely, benthic invertebrates exhibited greater differences between reference and impact sites. Procrustean analyses and Mantel tests indicated little concordance between reference site and impact site benthic invertebrate assemblages. Greater abundances of oligochaetes at impact sites and greater abundances of chironomids at reference sites contributed most to these differences, with the largest assemblage differences found at sites influenced by agriculture and sanitary dumps. Despite the fact that fishes and benthic invertebrates were structured along similar environmental gradients, little concordance was observed between assemblages. Wide annual fluctuations in the dominant taxa of each assemblage contributed most to the general discordance. Furthermore, discordant fish and invertebrate assemblages likely resulted because responses of each assemblage to anthropogenic impacts occurred at different scales of space and time.