Citation:

Reusser, D., H Lee II, W G. Nelson, J O. Lamberson, AND B. Thompson. EFFECTS OF NONINDIGENOUS SPECIES ON THE TAXONOMIC DIVERSITY OF ESTUARINE ASSEMBLAGES. Presented at 13th International Conference on Aquatic Invasive Species, Ennis, Ireland, September 19-23, 2004.

Description:

The effects of the few numerically dominant invasive species on benthic community abundance patterns has been documented in a number of estuaries. What is less appreciated is that the entire suite of nonindigenous species may alter the taxonomic composition of a community or biogeographic region. Recently, the "average taxonomic distinctness" (AvTD) and the "variation in taxonomic distinctness" (VarTD) have been proposed as measures of taxonomic breadth. AvTD measures the average taxonomic distance between pairs of species within an assemblage while VarTD measures variation in the taxonomic distance among species. These indices have been used to assess pollutant effects, but are used here to quantify the taxonomic diversity of nonindigenous species compared to the native species in two surveys of soft-bottom benthos. The first is the U.S. EP A's EMAP program, which conducted a probabilistic-based survey of the "small" estuaries of Oregon, Washington, and California (USA). The sampling frame included all Pacific Coast estuaries other than Puget Sound, San Francisco Estuary, and main stern of the Columbia River. A total of 842 benthic species were collected from 187 random benthic grabs taken from over 90 different estuaries/sub-estuaries. Of these species, 429 were native, 53 nonindigenous, 113 cryptogenic (species of uncertain origin), and 247 indeterminate (species that can not be classified). The second study was a compilation of monitoring programs within the San Francisco Estuary in which 235 native, 63 nonindigenous, 21 cryptogenic, and 212 indeterminate species were collected from 590 benthic grabs.

Our initial hypothesis was that nonindigenous species would have a lower taxonomic distinctness than the natives. However, there was no difference in AvTD between native and nonindigenous species among the small estuaries of the Pacific Coast or within the San Francisco Estuary. The lack of differences in AvTD does not appear to be a scale effect as there was no difference in AvTD between natives and nonindigenous species when evaluated within individual grabs from the EMAP survey. However there were differences among specific taxonomic groups, and the nonindigenous polychaetes had a significantly lower AvTD compared to the native polychaetes in both the Pacific Coast estuaries and the San Francisco Estuary, reflecting the high number of exotic spionid polychaetes in both studies. In contrast to Avid, VarTD was significantly higher in the entire suite of nonindigenous species than for the natives. Compared to a random subset of native species, the nonindigenous species display relatively greater diversity at the family and order levels. At least in these two studies, the suite of nonindigenous benthic species was not taxonomically impoverished compared to the natives, which reflects, in part, the mixing of invaders from different oceans and biogeographic zones. In contrast, previous studies have shown that pollution stress tends to reduce average taxonomic distinctness. Thus, invasive species and pollutants appear to have fundamentally different impacts on the taxonomic diversity and composition of benthic communities.

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