Data for early stages of sea-level rise lead to decreased salt marsh plant diversity through stronger competition in Mediterranean-climate marshes

Humans depend on ecological communities for invaluable ecosystem services that can be lost due to environmental degradation. Salt marshes provide many important ecosystem services including storm protection and nursery habitat for commercially-important species, but they are threatened by habitat destruction and sea-level rise (SLR). In salt marshes, community responses to SLR may be driven by a few dominant plant species. To better understand how SLR and interactions with Salicornia pacifica, the dominant species, will affect community diversity, I transplanted plots from the mid-marsh to two lower tidal elevations (10cm lower and 30 cm lower), removing the dominant species from half of the plots to distinguish the effects of SLR and dominant species. I monitored plant and invertebrate composition within these plots twice yearly for three years. For comparison, this experiment was also conducted at the nearby Tijuana River Estuary where single species are more dominant. Both dominant and subordinate plant species were affected by sea-level rise, and subordinate species cover and diversity were lower with large amounts of sea-level rise in the presence of S. pacifica than when it was removed. Invertebrate data were also collected and identified to order. The community-level response of salt marsh communities to SLR has rarely been addressed experimentally, and this project addresses that gap. In elucidating ways that community composition could shift with SLR, this study also contributes results that could be useful for managers planning for future SLR scenarios.