Reimagining South American coasts: unveiling the hidden invasion history of an iconic ecological engineer

Abstract

Aim The smooth cordgrass Spartina alterniflora is an iconic ecological engineer that has inspired some of the more insightful concepts and perspectives in modern theoretical ecology and environmental management, from population to community and ecosystem scales. Although it is currently considered native over more than 100 degrees of latitude along the Atlantic coast of the Americas, we challenge the default assumption that this cordgrass is native to South America, and propose an alternative hypothesis that it was introduced in the 18th or early 19th century by human activity.Location World-wide. Methods We applied nine criteria that have been proposed for the recognition of non-native species. These criteria consider the historical, biological, geographic, dispersal, ecological and evolutionary evidence that classically underpin the distinctions between native and non-native species. ResultsOur results strongly support the hypothesis that S. alterniflora is not native to South America. Herbarium collections, historical floristic descriptions and extensive literature reports clearly indicate that S. alterniflora was absent prior to the early 1800s in South America. S. alterniflora shows a reduced morphological, ecological and physiological variability along the South American coast and demonstrably increased in both regional extent and abundance over the 20th century. Main conclusionsWe conclude that what are now extensive S. alterniflora marshes in this region were probably bare mudflats and that there have been vast unrecorded and thus overlooked shifts in bird, fish and invertebrate biodiversity, and immense shifts in algal vs. detritus production, with the concomitant trophic cascades that these changes imply. Our results change the way we perceive "natural" coastal ecosystems on the Atlantic coast of South America as a whole. Indeed, most South American coastal marshes currently are what we term "ecological mirages"-illusions that have seriously hampered our ability to recognize the nature of pre-existing native ecosystems.

Invasive species denialism: Sorting out facts, beliefs, and definitions

“…Overgrowth of bare mudflats is more debatable (after all, that is what all cordgrasses do, regardless of their origin), but increasing costs of managing wildlife (i.e., eliminating the introduced seagrass), and interfering the human uses of estuaries is clearly contradictory with the fact that they should be protected where they are native (i.e., not wiped out by grazing by cattle or for urbanization). The smooth cordgrass, Spartina alterniflora , historically assumed to be an indigenous, highly valued feature of the Atlantic coasts of South America, was suggested to have catastrophically (our emphasis) altered the pristine state of nature when its native status was questioned (Bortolus, Carlton, & Schwindt, ). Although many arguments on the positive and negative effects of NIS are disputable, some are plainly untenable.…”

SupportingSpartina: Interdisciplinary perspective showsSpartinaas a distinct solid genus

“…In modern times, Spartina species have played a major role in long‐term studies of coastal environmental engineering, inspiring the “ecological mirages hypothesis” (Bortolus et al. ), and in conservation ecology relative to coastal accretion and marsh creation, as well as of linkages to primary and secondary production of fauna species worldwide (Costa and Davy , Adam , Bertness , Gan et al. , Silliman et al.…”

“…In fact, S. alterniflora and S. anglica are responsible for some of the largest continental‐scale bioinvasion events ever recorded in Asia (Qiu ) and the Americas (Bortolus et al. ) having reshaped vast coastal‐marine ecosystems and altered coastal geomorphology, biodiversity, and primary and secondary productivity. These invasions resulted in striking, cascading socioeconomic impacts (Li et al.…”

“…Species such as S. alterniflora figured prominently in agriculture and botany in the colonial Americas (Elliott 1821, Barlett 1908, as well as in pioneer works on coastal biogeography (Chapman 1960). In modern times, Spartina species have played a major role in long-term studies of coastal environmental engineering, inspiring the "ecological mirages hypothesis" (Bortolus et al 2015), and in conservation ecology relative to coastal accretion and marsh creation, as well as of linkages to primary and secondary production of fauna species worldwide (Costa and Davy 1992, Adam 1993, Bertness 1999, Gan et al 2009, Silliman et al 2009).…”

“…This species is one of the "100 World's Worst Invasive Alien Species" and is widely regarded as an aggressive nonnative species in Europe, the North American Pacific coast, South American Atlantic coast, China, New Zealand, Australia and South Africa. In fact, S. alterniflora and S. anglica are responsible for some of the largest continental-scale bioinvasion events ever recorded in Asia (Qiu 2013) and the Americas (Bortolus et al 2015) having reshaped vast coastal-marine ecosystems and altered coastal geomorphology, biodiversity, and primary and secondary productivity. These invasions resulted in striking, cascading socioeconomic impacts , Strong and Ayres 2009, Wan et al 2009, Saarela 2012, Luque et al 2014, Yin et al 2015.…”