How does invasive Spartina densiflora respond to contrasting environmental conditions in its native region?

Abstract

Coastal salt marshes are recognized worldwide as diverse and productive environments, providers of many ecosystem services, and as places where a wide variety of taxa live, nest, nurse, and/or feed. Along the Atlantic coast of South America, the austral cordgrass Spartina densiflora displays great phenotypic variations that may favor it to thrive on a wide range of substrates, inhabiting not only the typical soft bottom marshes, but also on cobble beaches and rocky shores. These Patagonian rocky salt marshes, unlike other salt marshes, develop predominantly on top of wave-cut platforms made of sedimentary rock, highly exposed to wave action, and with a dwarf Patagonian phenotype of S. densiflora commonly dominating the vegetation. In this work we evaluate experimentally the hypothesis that this phenotype is a plastic response that maximizes the survival of S. densiflora on rocky bottom environments exposed to wave action. Our results strongly suggest that the austral cordgrass S. densiflora is able to adjust its morphological characteristics in relation to contrasting environmental changes, allowing it to survive in a broad spectrum of coastal environments, including rocky shores with little accumulation of mud and high wave exposure. The typical plants transplanted from the muddy marsh to the rocky marsh exhibited lower height (80%) than the typical control in muddy marsh and than the Patagonian plants in rocky marsh (38%), additionally the typical transplants in the rocky marsh showed no visible damage to their leaves or stems. Our research provides new evidence to understand the success of this species across non-native regions worldwide where it is considered an aggressive invasive bioengineer.