The study aimed to investigate patterns of spatial and temporal variability of mobile macroinvertebrate assemblages associated to coralligenous habitat. A multi-factorial sampling design was used to test the hypotheses that the structure of assemblages and their spatial and temporal variability changed in relation to substrate inclination. Moreover, macroalgae and sessile macroinvertebrates were also investigated in order to detect eventual relationships between sessile and mobile assemblages. A total of 236 mobile macro-invertebrate taxa were identified, among them 2 Platyhelminthes, 4 Sipuncula, 6 Nemertea, 27 Mollusca, 86 Annelida, 103 Arthropoda, 8 Echinodermata. The results of the study show that mobile macro-invertebrate assemblages of coralligenous habitat were little influenced by the inclination of substrate and by the morphology of sessile organisms, as patterns of variation were different between the two assemblages. Mobile macro-invertebrate assemblages changed among sampling dates within a one-year period and showed high variability at the spatial scale examined.

1. Whilst the successful establishment and spread of invasive species can be determined by above-ground processes, results are often equivocal. Emergent research, mostly from terrestrial ecosystems, demonstrates that below-ground processes (nutrient cycling, chemical properties) under microbial control can mediate interactions between native and invasive plants. Because microbes can control similar sediment properties in marine ecosystem that influence plant fitness, we argue that below-ground properties should also exert strong control interactions between native and invasive marine macrophytes.2. We coupled surveys of microbial communities and chemistry of sediments collected from an invasive alga (Caulerpa cylindracea), a native competitor (the seagrass Posidonia oceanica) and unvegetated sediments with a large field experiment, in which we manipulated the presence/absence of the canopies of both species to determine the effects of above-and below-ground processes on the success of C. cylindracea. Posidonia oceanica and C. cylindracea sediments have microbial communities andpredicted metabolic process that reflect aerobic and anaerobic conditions, respectively. Moreover, the nutritional quantity of organic matter was higher, but quality lower in C. cylindracea sediments compared to the two native habitats. The growth of C. cylindracea fragments was equally low in the presence or absence of a P. oceanica canopy, whereas the growth of C. cylindracea was higher in the canopy removed vs. present treatment, possibly because, in the absence of a C. cylindracea canopy, fragments are released from intraspecific competition for resources. 4.Synthesis. Sediment/soil processes are increasingly recognized as important drivers of the success and hence impacts of invasive plants. We extended this theory to marine ecosystems and suggest biotic resistance to invasion may not always be attributable to intact canopies, but may also result from indirect effects of native | 2083Journal of Ecology GRIBBEN Et al.

No abstract

No abstract