546 www.frontiersinecology.org © The Ecological Society of America Write Back hypothesis. In our first hypothesis, exemplified by the metaphor of the “low-hanging fruit”, the lion’s share of our capacity to explain and predict is made possible by long-established theories. The “explanation of resid- ual variation” described by Patten and Hartnett could have been substi- tuted with our use of the term “mar- ginal explanatory power”. We did not, however, speculate on the advent of a “paradigm shift” in ecology or the advent of a new crop of fruit. We do not identify as philosophers or historians of science, but we do feel the portrayal by Patten and Hartnett of “paradigm shift” in con- trast to “normal science”, sensu Kuhn, is not entirely adequate, even if this distinction may be highly sub- jective. We would suspect that para- digm shifts are accompanied by leaps in R 2 in the specific context that the advancement applies. While the dis- covery of relativity could undoubt- edly be labeled a “paradigm shift”, it is not because this theory offered a step improvement on Newton’s the- ories. Rather, Einstein’s theory pro- vided explanatory and predictive power (R 2 ’ 1) in a context where Newton’s theory failed (R 2 ’ 0) – the prediction and explanation of the movement of extremely large objects or movement at extreme speeds – while also providing expla- nation and prediction in all contexts where Newtonian physics had not been falsified. The effect of “para- digm shifts” on explanatory power or complexity is a suitable question for future metaknowledge studies. We likely have not presented an exhaustive list of the possible mech- anisms for the observed trends in R 2 and number of P values in ecology. These trends may be best explained by hypotheses that make reference to “normal science” and “paradigm shifts” as suggested by Patten and Hartnett, beyond what is included in the “low-hanging fruit” hypothesis. We would suggest that further meta- knowledge studies are required to discern between proposed hypothe- ses and to accurately describe the state of our discipline. Etienne Low-Décarie *† , Corey Chivers, and Monica Granados Department of Biology, McGill University, Montreal, Canada; † Current address: School of Biological Sciences, University of Essex, Colchester, UK * (elowde@essex.ac.uk) doi:10.1890/14.WB.015 Rapidly spreading seagrass invades the Caribbean with unknown ecological consequences The non-native seagrass Halophila stip- ulacea has spread rapidly throughout the Caribbean Sea (Willette et al. 2014); without additional research, the ecological ramifications of this invasion are difficult to predict. Biodiversity, connectivity of marine ecosystems, and recovery of degraded coral reefs could all be affected. The invasive seagrass, native to the Red Sea and Indian Ocean, has taken over sand bottoms and intermixed with or replaced native seagrasses, including Thalassia testudinum, Syringodium fili- forme, and Halodule wrightii (Figure 1). H stipulacea is an established inva- sive species in the Mediterranean Sea, probably introduced after the opening of the Suez Canal. Com- petition between H stipulacea and native Mediterranean seagrasses is minimal to absent due to habitat pref- erences; H stipulacea grows in deeper, bare sand habitats and over sub- merged dead mats of native seagrass (Sghaier et al. 2011). The only other known invasive seagrass species, Zostera japonica, has displaced a native seagrass at some locations off the coast of the Pacific Northwest (Jun Bando 2006). Experimental introduction of Z japonica to bare mud flats increased the density and num- ber of animal species observed therein (Posey 1988). Sediment disturbance, such as the excavation of underwater substrate by storms, provides an advantage to both of these faster- growing invasives over their native counterparts (Jun Bando 2006; Willette and Ambrose 2012). In the Caribbean, H stipulacea could stabilize previously unvege- tated sand bottoms, thereby reducing erosion of nearby coastal shorelines during storm events, which are expected to become more frequent and stronger under a changing cli- mate. Improved understanding of the potential effects of this invasive sea- grass in the Caribbean requires more Figure 1. The invasive seagrass Halophila stipulacea (bright green, short elliptic/oblong blades 3–8 cm long, with distinct mid-veins) growing intermixed with Thalassia testudinum, Halodule wrightii, and Syringodium filiforme near St John, in the US Virgin Islands. CS Rogers