Effects of sediment and salinity on the growth and competitive abilities of three submersed macrophytes

• Microcosm tested salinity and sediment effects on SAV growth and competition.
• H. dubia was sensitive to salinity while V. americana preferred muddy substrate.
• H. dubia and V. americana were stronger competitors compared with S. pectinata.
• Positive interactions provide support for multi-species restoration.

Submersed macrophytes are generally found in multispecies beds, with the dominance of individual species varying in both space and time. In estuarine environments, these plants can grow across a range of environmental conditions which may alter species interactions. Three species common to the Chesapeake Bay region, Vallisneria americana (wild celery), Heteranthera dubia (water stargrass), and Stuckenia pectinata (sago pondweed), were planted in a microcosm designed to test their growth and interactions (relative yielding) under a range of conditions of salinity (0, 5, or 10), sediment type (mud or sand), and species combinations. H. dubia was most sensitive to elevated salinity, while sediment type impacted only V. americana, performing better in mud compared with sand. V. americana and H. dubia were strong competitors, overyielding in many treatments when grown in mixture, while S. pectinata never overyielded and frequently underyielded. Interspecific competition was only strong between H. dubia and S. pectinata under 0 salinity, regardless of sediment type. V. americana on the other hand, showed strong interspecific competition with S. pectinata across multiple salinity and sediment types, indicating that this species is able to compete well across a wider range of environmental conditions. Our results suggest that H. dubia and V. americana are strong candidates for multi-species restoration, as positive interactions were observed when grown together. This measure of complementarity provides evidence for increased mixed bed plant performance under environmental conditions that would typically be more stressful to each growing alone.