Abstract
As part of a multi-year field study to investigate plankton dynamics in the Lower Columbia River Estuary (LCRE), we conducted monthly sampling of the mesozooplankton (> 73 μm) at a station near Astoria, Oregon. The planktonic copepod community was numerically dominated by three non-indigenous species (NIS), Pseudodiaptomus forbesi, Limnoithona tetraspina, and Sinocalanus doerrii, and two native species, Eurytemora affinis and Diacyclops thomasi. However, seasonal co-occurrence of non-indigenous and native copepods was highly variable between species-pairs. The native E. affinis and the non-indigenous S. doerrii showed the greatest temporal overlap (March-October), but other species-pairs also showed periods of considerable overlap during some seasons (e.g., E. affinis and P. forbesi in June-September). Spatial co-occurrence of native and non-indigenous species was also examined in temperature and salinity “space” (rather than geographic space): all six species-pairs (3 non-indigenous species × 2 native species) showed some degree of overlap, with the greatest (proportional) overlap occurring between the native E. affinis and the two nonindigenous species, S. doerrii and P. forbesi. This suggests the potential for competition to occur between native and non-native copepods in the LCRE, although with variation between seasons and species. Future studies are recommended that explicitly test for and distinguish between the relative importance of biological (e.g., competition and predation) and physico-chemical processes (e.g., freshwater runoff, eutrophication) in regulating the population dynamics of native and invasive copepods in the LCRE.
Highlights
There have been many studies detailing the economic and ecological impacts of nonindigenous species (NIS) that invade terrestrial, marine and freshwater habitats
Three species of non-indigenous planktonic copepods were abundant in our samples: Pseudodiaptomus forbesi, Limnoithona tetraspina, and Sinocalanus doerrii (Figure 2B)
Two species of native planktonic copepods were abundant in our samples – Eurytemora affinis (Poppe, 1880) and Diacyclops thomasi (Forbes, 1882) (Figure 2C)
Summary
There have been many studies detailing the economic and ecological impacts of nonindigenous species (NIS) that invade terrestrial, marine and freshwater habitats. Though there are numerous cases of invasive planktonic animals, only a few have been studied in detail (Bollens et al 2002) These plankton invaders can have profound ecological and economic impacts, the most notorious and well-studied being the ctenophore Mnemiopsis leidyi (Agassiz, 1865) in the Black and Caspian Seas (Shiganova et al 2004; Daskalov and Mamedov 2007; Roohi et al 2008; Roohi et al 2010). In North America, exotic planktonic crustaceans have been successful, with eight planktonic copepod invaders documented in coastal rivers and their estuaries (Cordell et al 2008), and at least 10 other nonindigenous planktonic copepod and cladoceran species occurring in inland fresh waters (USGS 2009). Bythotrephes can have large effects on invaded plankton communities including negative effects on some of its competitors (Foster and Sprules 2009), declines in plankton species richness (Yan et al 2002; Strecker et al 2006), and reductions in total community biomass and abundance (Yan et al 2001; Boudreau and Yan 2003; Strecker and Arnott 2005; Strecker et al 2006; Strecker and Arnott 2008)
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