Differential physico-chemical tolerances of amphipod species revealed by field transplantations

Abstract

Physico-chemical regimes of river systems are major determinants of the distributions and relative abundances of macroinvertebrate taxa. Other factors, however, such as biotic interactions, may co-vary with changes in physico-chemistry and concomitant changes in community composition. Thus, direct cause and effect relationships may not always be established from field surveys. Equally, however, laboratory studies may suffer from lack of realism in extrapolation to the field. Here, we use balanced field transplantation experiments to elucidate the role of physico-chemical regime in determining the generally mutually exclusive distributions of two amphipod taxa, Gammarus (two species) and Crangonyx pseudogracilis. Within two river systems in Ireland, the former species dominate stretches of well oxygenated, high-quality water, whereas the latter dominates stretches of poorly oxygenated, low-quality water. G. pulex and G. duebeni celticus did not survive in bioassay tubes in areas dominated by C. pseudogracilis, which itself survived in tubes in such areas. However, both C. pseudogracilis and Gammarus spp. survived equally well in tubes in areas dominated by Gammarus spp. Physico-chemical regime thus limits the movement of Gammarus spp. into C. pseudogracilis areas, but some other factor excludes C. pseudogracilis from Gammarus spp. areas. Since previous laboratory experiments showed high predation rates of Gammarus spp. on C. pseudogracilis, we propose that predation by the former causes exclusion of the latter. Hence, presumed effects of physico-chemical regime on macroinvertebrate presence/abundance may often require experimental field testing and appreciation of alternative explanations.

Replacement of a native freshwater macroinvertebrate species by an invader: implications for biological water quality monitoring

“…Our findings reinforce this view, as G. pulex seemed to greatly over-inflate scores in poor quality areas, where in many sites it was the highest scoring BMWP group, despite routinely co-occurring with very tolerant taxa such as isopods, chironomids and oligochaetes. This view is reinforced when the North American Crangonyx pseudogracilis Bousfield is considered, as this is found in even lower water quality areas than G. pulex in N. Ireland and the Isle of Man (MacNeil et al, 2000(MacNeil et al, , 2009. For instance, although G. pulex has replaced G. d. celticus in lower water quality areas of rivers such as the Lagan, in even more grossly polluted areas, both these Gammarus spp.…”

“…are absent. Interestingly, the family Crangonyctidae is grouped with the Gammaridae in the BMWP scoring system, increasing the scope for flawed assessments of biological water quality (MacNeil et al, 2000). The influence of relatively high scoring amphipods such as C. pseudogracilis or G. pulex will be disproportionately high in very poor water quality sites where there tends to be a depauperate and low scoring assemblage, and this disparity will increase as water quality decreases.…”

“…The BMWP system assigns scores to macroinvertebrate families based on their perceived relative sensitivities to organic enrichment. However, some invasive species are far more pollution tolerant than natives (Dick & Platvoet, 1996;MacNeil et al, 2000) and are capable of surviving rigorous introduction mechanisms that allow them to enter river systems where environmental degradation has diminished native assemblages (den Hartog et al, 1989;Conlan, 1994;MacNeil et al, 2004). The BMWP and other indices do not distinguish between native and invasive species within the same family, even when they differ in sensitivity to organic pollution (Walley & Hawkes, 1996;MacNeil et al, 2000).…”

“…Since the 1940s and 1950s, populations of the native Gammarus duebeni celticus Stock & Pinkster in the Isle of Man (an island of 500 km 2 in the Irish Sea) and N. Ireland, respectively, have been subjected to invasion by Gammarus pulex (L.) introduced from England (Strange & Glass, 1979;Dick et al, 1997;MacNeil et al, 2009). Native and invasive species such as G. d. celticus and G. pulex in N. Ireland and the Isle of Man, are also 'lumped' together as 'Gammaridae' in the BMWP index and assigned the same score (MacNeil et al, 2000). In many river systems in N. Ireland and the Isle of Man, G. d. celticus has replaced G. pulex, through intraguild predation (IGP) (see Polis et al, 1989;Dick, 2008) and lower dissolved oxygen levels and higher levels of organic pollution favour IGP of G. d. celticus by G. pulex in N. Irish rivers (MacNeil et al, 2004).…”

Enhanced fecundity and parasite release in the first amphipod invader on the Iberian Peninsula

“…Crangonyx pseudogracilis seems to thrive best in marginal habitats, particularly shallow eutrophic waters , rich in macrophytes and/or roots (Grabowski et al, 2012). Generally, this species is associated to low water quality (polluted and low oxygen content) but it is also able to colonize areas of high water quality (MacNeil et al, 2000). Thus, it is possible that C. pseudogracilis will be able to invade nearby water bodies and poor-quality rivers which are very common in the study area.…”