Seasonal variability in the grazing potential of the invasive amphipod Gammarus tigrinus and the native amphipod Gammarus salinus (Amphipoda: Crustacea) in the northern Baltic Sea

Abstract

Mesograzers are known to reduce the biomass of their host plant and modify the structure of the whole macrophyte community in many ecosystems. Thus, the introduction of an efficient mesograzer may destabilize macrophyte community and also affect the native grazers. We estimated how large proportion of macrophyte production are consumed by the alien gammarid G. tigrinus and the native gammarid G. salinus in the species poor ecosystem of the northern Baltic Sea. We analysed whether G. tigrinus consumes different diet as the native G. salinus and whether the effect of G. tigrinus on the survival of the native G. salinus is macrophyte species specific. Grazing experiments showed that there was a clear difference in the grazing rates of gammarids among the studied macrophyte species in summer and autumn but not in spring. The grazing rates were significantly higher in the prevailing macrophyte Pilayella littoralis as compared to other macrophytes. The grazing was inversely related to the diurnal net photosynthetic values of macrophytes. The gammarid amphipods potentially removed only a minor part of plant primary production except for summer and autumn when grazing of a few perennial species exceeded macrophyte production. Macrophyte species and presence of G. salinus had no effect on the survival of G. tigrinus. The presence of G. tigrinus, however, reduced the survival of the native gammarids within P. littoralis in summer. To conclude it is likely that both native and alien gammarid amphipods do not exert significant pressure on the macroalgal communities in the northern Baltic Sea. Competitive interactions between G. tigrinus and G. salinus within the prevailing macrophyte P. littoralis is the likely explanation of the decline of the native gammarid amphipods after the establishment of G. tigrinus in the northern Baltic Sea.

Potential impact of invasive amphipods on leaf litter recycling in aquatic ecosystems

“…Previous studies from the Netherlands (Pinkster et al 1977) and Northern Ireland (Dick 1996) highlighted the predation of invertebrates and fish eggs by this invasive species. However, some experimental studies have shown that G. tigrinus also consumes different types of algae (Orav-Kotta et al 2009) and Rong et al (1995) observed the consumption of leaf litter. Due to the differential leaf litter breakdown rates between native and invasive species and the decrease in amphipod biomass, the replacement of native species by invaders should lead to a strong decrease in leaf litter recycling in rivers.…”

Differences in stress tolerance and brood size between a non-indigenous and an indigenous gammarid in the northern Baltic Sea

“…However, its effective spread and dominance may also be due to earlier maturation and greater brood size (both traits were indicated in these experiments), faster juvenile growth, longer and more frequent reproductive periods, higher reproduction rates and greater longevity. Additionally, G. tigrinus predates on indigenous species (Grabowski et al 2007b) as well as other non-indigenous species (Platvoet et al 2009) and it is also said to be a strong competitor for food and habitat (Orav-Kotta et al 2009). All these traits may further contribute to its dominance and success.…”

Behavioural and physiological responses to ­pharmaceutical exposure in macroalgae and ­grazers from a Baltic Sea littoral community

“…Non-linear responses are common in experiments testing pharmaceuticals and other emerging substances (e.g. Calabrese & Baldwin 2001, De Lange et al 2006, 2009, Eriksson Wiklund et al 2012 in press). Although the measured effect concentrations are higher than environmental concentrations, the traditional predicted environmental concentrations (PEC) to predicted no-effect concentration (PNEC) ratio approach in risk assessment would indicate a high relevance to the environment (Cleuvers 2005).…”

“…and macroalgae like F. vesiculosus are interdependent and constitute an important key community of the Baltic Sea (Råberg & Kautsky 2007). By feeding on the macroalgae, the amphipods both degrade the macroalgae itself and remove impeding epibiota (Orav-Kotta et al 2009). Consequently, the amphipods affect the macroalgal structure and productivity (Arrontes 1999) and constitute an important link in the littoral community, connecting primary producers to secondary consumers in the coastal zone (MacNeil et al 1999).…”