Georgia marshes

My current research centers on climate change impacts to tidal wetlands such as salt marshes in the Pacific Northwest. I also worked in these ecosystems as a graduate student in San Diego. So, for years I have become familiar with the scientific literature on the organisms and ecology of coastal wetlands. Though I have only conducted research on the west coast, much of the literature about the plants and algae of tidal wetlands, and the ecology of these ecosystems, has come from the east and Gulf coasts of the US. So, many of the species and research sites have familiar names, but until this month I had never been in an Atlantic marsh.

Last weekend I attended the Benthic Ecology Meeting in Savannah, Georgia. There were scientific talks on fishes, coral reefs, oyster beds, and of course, salt marshes. One of the highlights of the meeting was a short underwater film festival called “Beneath the Waves”, an effort now in its fourth year. We viewed a series of short films about marine conservation, marine ecosystems and human relationships with the environment. Some of the films were produced by graduate students. Overall, the subset of films I saw at the conference were of very high quality and I highly recommend any chance to see them.



Spartina marsh with wrack.

The conference events absorbed most of my three day trip to Georgia, but after the final session of talks I snuck away for two hours down the Savannah River towards Tybee Island to see what I could of Georgia’s marshes.

The tidal wetlands of the Atlantic coast are extensive, so it was not long before I ran into waterways and wetlands. I stopped for a while at Ft. Pulaski National Monument and walked along a trail that ran parallel to the river. It wasn’t a particularly impressive marsh, but it was my first chance to see an east coast tidal wetland. There was the iconic Spartina alterniflora, a grass species that tends to form monocultures in low marsh. From my experience with the scientific literature, it is probably the most well-studied salt marsh plant in the world.

I also saw salt grass, Distichlis spicata (we have this species on the west coast as well), a species of Juncus, pickleweed, and some shrubs at the margins of the marsh. The notorious Littorina was also common. It is a dime-sized snail that has been the cause of some of the extensive marsh die-offs in Atlantic marshes. Research by Brian Silliman suggests that a simple trophic cascade can lead to marsh die-off: reductions in blue crab numbers (due to human harvest) results in an increase in the herbivorous snails and a decline in marsh plants.




Spartina alterniflora shoots with a few
 Littorina snails at the base of the plants.

 Overall the east coast salt marshes do not seem to be particularly species rich. Spartina steals most of the show. We seem to have more species and more complex assemblages in the Pacific Northwest (e.g., Jefferson 1975). However, ecological interactions among species and their environment seem to be much better understood in the Atlantic marshes due a rich tradition field experimentation, and perhaps, because those less-diverse communities are more tractable ecologically.

Atlantic salt marsh ecology has contributed to important insights into the factors that limit species distributions. For instance, salt-tolerant species (“halophytes”) tend to be excluded from fresher environments because of poor competitive ability with other species, not because they cannot tolerate fresher conditions (Crain et al. 2004). Salt-intolerant plants, on the other hand, cannot handle the level of environmental stress present in more saline marshes. Moreover, the spatial distribution of some plant species can be extended by the presence of other species because the latter essentially create more benign environmental conditions; Hacker and Bertness (1995) showed that the rush Juncus ameliorated soil salinity stress for the shrub Iva thereby allowing it to persist in lower tidal environments than might otherwise be favorable. Plant assemblages in other geographic regions – with different sets of species and different climates – may be structured differently, but the Atlantic marsh research has established useful groundwork for continued advances in tidal wetland ecology.

References

Crain et al. 2004 Ecology 85:2539
Hacker and Bertness. 1995. Ecology 76:2165
Jefferson 1975. Oregon State Univ PhD dissertation.