Abstract
Different irrigation or ventilation strategies by macrofauna may provide a competitive advantage to tolerant species invading impacted benthic systems and alter benthic-pelagic coupling. To comparatively analyze the effects of an exotic and a native polychaete burrower on sediment-water exchanges, two laboratory experiments were performed. In the first experiment, the invasive spionid polychaete Marenzelleria neglecta was added to defaunated sediments and fluxes of the inert tracer (bromide, Br−) were measured to quantify the effects of irrigation by the worm on the tracer transport. In the second experiment, M. neglecta or the native polychaete Hediste diversicolor were introduced to a relatively diverse Baltic soft-bottom macrofauna community. The effect of species on fluxes of reactive solutes (ammonium, NH4+, and phosphate, PO43−) and transport rates of Br− was estimated. The results indicate different invasion effects depending on the characteristics of the recipient habitat. In defaunated sediments, a single specimen of M. neglecta significantly enhanced originally low solute exchange rates. Total tracer flux was significantly enhanced over diffusive flux by a factor of 1.6 ± 0.14 (n = 3). In natural sediments, on the other hand, the addition of either M. neglecta or H. diversicolor had no statistically significant effects on benthic fluxes. Tracer flux estimates between control and treatment incubations differed by less than 10% on average, and both reactive solutes tended to increase by 10 to 40% after additions. One specimen of M. neglecta in cores with defaunated sediment generated approximately 20% of the tracer flux produced by the relatively diverse macrofauna community. Estimated net tracer fluxes in two experiments corresponded well with the number of adult polychaetes found in sediments (r2 = 0.73, p = 0.005, n = 12). The invasive M. neglecta produced a small effect on fluxes in biodiverse sediments, comparable to those of H. diversicolor, but it may deeply alter porewater chemistry in azoic sediment. As M. neglecta tolerates chemically reduced and sulphidic conditions, its bioirigation may favor sediment reoxidation and ultimately the recolonization by less tolerant, native species.
Highlights
Understanding and evaluating the functional role of individual species is linked to the growing awareness of invasion phenomena in marine ecology [1,2,3,4,5,6]
Total tracer flux was significantly enhanced over diffusive flux by a factor of 1.6 ± 0.14 (n = 3)
Tracer flux estimates between control and treatment incubations differed by less than 10% on average, and both reactive solutes tended to increase by 10 to 40% after additions
Summary
Understanding and evaluating the functional role of individual species is linked to the growing awareness of invasion phenomena in marine ecology [1,2,3,4,5,6]. There is a need to quantify the impacts of species in recipient ecosystems [7,8,9] and to gain more knowledge regarding the extent of changes in biogeochemical cycling caused by invasions [10,11]. The role of functional redundancy (i.e., several species performing the same functions) may be as important as or even more important than species richness [19,20]. It seems that the effect of an invasive species on the recipient ecosystem and its (biogeochemical) functions may depend on both species richness and functional diversity
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