Disturbance to ecosystems comes in many forms, including climatic changes, anthropogenic influences, and introductions of invasive species. As with other forms of disturbance, species invasions can cause pronounced disruptions, predominantly through resource exploitation and rapid biomass accumulation, and a corresponding exclusion of other species. This continued inundation may stall or prevent the recovery of native species, resulting in ecosystem regime shifts with long-term consequences for ecosystem diversity and functioning. While the physical and chemical consequences of species invasions are well-studied, whether there is a microbial component aiding in invasion strategies is an outstanding ecological question. Here, we tracked a temperate kelp forest ecosystem undergoing a significant regime shift from native (Macrocystis pyrifera) to invasive (Sargassum horneri) macroalgal-dominated, monitoring perturbations in the microbiomes in conjunction with the proliferation of an invasive species through time. Specifically, we used whole genome shotgun metagenomic sequencing to characterize the shifts in kelp forest microbiome structure and function along a temporal trajectory of the invasive alga’s spread until early ecosystem recovery, and infer the potential of altered microbiomes to influence the health and future recovery of the native kelp.
Results/Conclusions
Overall, we found significant compositional distinctions in the microbiome of invasive alga S. horneri to the microbiome of the native kelp, M. pyrifera; most notably the enrichment of potential pathogens including Vibrios. During the early signs of ecosystem recovery, the native and invasive algae coexisted within the kelp forest; however, we observed extensive tissue damage on the native kelp where the two species were in direct contact. We hypothesized that the tissue damage was a direct result of inoculation of the pathogen-enriched Sargassum microbiome onto the native kelp; however, our metagenomic description of the microbiome did not support this hypothesis. Rather, we found evidence of microbiome dysbiosis on the bleached kelp. We did, however, detect evidence of Sargassum microbiome inoculation into the surrounding environment, specifically onto the benthic substrate directly underneath the canopy. At sites where this benthic microbiome shift occurred, there was a corresponding delay in native kelp recovery despite favorable environmental conditions for recruit proliferation. Previous studies show that benthic microbiome composition and functional potential affect the recruitment success of macroalgal propagules; thus, our results suggest that the microbiome perturbations may have a negative impact on kelp recruitment. Our study suggests that ecosystem disturbance caused by invasive species may be magnified by microbial perturbations, which may further delay the future recovery of native populations.