The influence of marine invasive species on native seagrasses: a brief overview highlighting research gaps and biases

Seagrasses are angiosperms widespread among many coastal regions although absent from others. Over most of their distribution range, these ecosystem engineers are experiencing declines due to a wide range of small- and large-scale stressors. Among the latter, we briefly reviewed the influence of marine invasive species that are colonizing and interacting with native populations of seagrasses. Our study scanned the literature and compiled 73 studies that allowed us to outline the threats these invaders pose to seagrass beds and their associated communities. Invasive species included various primary producers and a variety of consumers, epiphytes and bioturbators. Based on number of studies alone, competitive interactions were the most common mechanism of seagrass disruption. Most of the effects reported were negative and affected a variety of seagrass traits, including but not restricted to shoot density, size, photosynthetic rates, growth, productivity, rhizome stability, reproduction, quality, and survival. These effects varied widely in strength and with seagrass species, type of invader and location, and included a few cases where no effects or evidence of resistance to invasion were reported. A concentration of studies on two seagrass species and a few coastal regions also suggests strong taxonomic and geographic biases on the research available. The influence of invasive species is not isolated from other disturbances, particularly anthropogenic stressors, so they were most detrimental upon seagrasses in already poor condition. More mitigation or restoration efforts are needed to alleviate the multiple effects of invasive species and improve the sustainability of these critical habitat-forming species.