Functional role of native and invasive filter-feeders, and the effect of parasites: learning from hypersaline ecosystems

摘要

Filter-feeding organisms are often keystone species with a major influence on the dynamics\udof aquatic ecosystems. Studies of filtering rates in such taxa are therefore vital in order to\udunderstand ecosystem functioning and the impact of natural and anthropogenic stressors\udsuch as parasites, climate warming and invasive species. Brine shrimps Artemia spp. are the\uddominant grazers in hypersaline systems and are a good example of such keystone taxa.\udHypersaline ecosystems are relatively simplified environments compared with much more\udcomplex freshwater and marine ecosystems,making themsuitablemodel systems to\udaddress these questions. The aimof this study was to compare feeding rates at different salinities\udand temperatures between clonal A. parthenogenetica (native to Eurasia and Africa) and\udthe invasive American brine shrimp A. franciscana, which is excluding native Artemia from\udmany localities.We considered how differences observed in laboratory experiments upscale\udat the ecosystem level across both spatial and temporal scales (as indicated by chlorophyll-a\udconcentration and turbidity). In laboratory experiments, feeding rates increased at higher temperatures\udand salinities in both Artemia species and sexes, whilst A. franciscana consistently\udfed at higher rates. A field study of temporal dynamics revealed significantly higher concentrations\udof chlorophyll-a in sites occupied by A. parthenogenetica, supporting our experimental\udfindings. Artemia parthenogenetica density and biomass were negatively correlated with chlorophyll-\uda concentration at the spatial scale.We also tested the effect of cestode parasites,\udwhich are highly prevalent in native Artemia but much rarer in the invasive species. The cestodes\udFlamingolepis liguloides and Anomotaenia tringae decreased feeding rates in native\udArtemia, whilst Confluaria podicipina had no significant effect. Total parasite prevalence was\udpositively correlated with turbidity. Overall, parasites are likely to reduce feeding rates in the\udfield, and their negative impact on host fecundity is likely to exacerbate the difference between\udgrazing rates of native and alien Artemia populations at the ecosystem level. The results of\udthis study provide evidence for the first time that the replacement of native Artemia by A. franciscana\udmay havemajor consequences for the functioning of hypersaline ecosystems. The\udstrong effect of parasites on feeding rate underlines the importance of taking parasites into\udaccount in order to improve our understanding of the functioning of aquatic ecosystems