Biological and physical factors affecting the colonization of vegetation-free patches in a SW Atlantic salt marsh

Abstract

In many Northern Hemisphere salt marshes, recovery of disturbance-generated bare areas usually occurs within a few years. However, in some southwestern Atlantic marshes, bare patches may remain unchanged for several years. Here we investigated biological and physical factors that might affect bare patch colonization in a Mar Chiquita coastal lagoon salt marsh (Argentina). We evaluated natural seedling emergence of the pioneer pickleweed plant Sarcocornia perennis, considering distance to mature plants and the herbivory/bioturbation exerted by the crab Neohelice granulata (using exclosures). Almost no seedling emergence was observed in patches distant from mature plants, while higher emergence resulted in close patches. Crab exclusion did not affect seedling counts. Nevertheless, most of these seedlings did not survive high-temperature months. We analyzed if colonization was favored by increasing the availability of S. perennis seeds, and we found similar seedling emergence in patches both close and distant to mature plants. As in the previous experiment, most of them did not survive the high-temperature months, but some seedlings could establish within crab exclosures. Finally, we used a shade cloth to reduce solar radiation, but this did not increase seedling survival, which was only favored in crab exclosures. In summary, our results suggest that seed availability, followed by the presence of crabs (but not solar radiation), affect the rate of patch recovery. Additionally, our results show that life-history traits (seed ecology) of the colonizer can be a key and are a usually overlooked driver of salt marsh secondary succession.