PARENT SESSION
Oral Session # 54: Coastal Ecosystems: Salt Marshes.
Presiding: P Ringold
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.
Will the marsh paradigm hold? Spartina distributions along the length of the Altamaha River Estuary, GA.
White, Susan*,1, Alber, Merryl1, 1 University of Georgia, Athens, GA
ABSTRACT- In the Altamaha River estuary in Georgia, S. alterniflora and S. cynosuroides are the dominant plant species in salt and brackish marshes, respectively. The general paradigm for zonation in salt marshes is that stress tolerance and competition combined drive vegetation patterns within a single marsh. However, it is unclear if the stress tolerance/competition paradigm can be applied along an estuarine gradient. Two field experiments established in Spring 2001 examined factors that control S. alterniflora and S. cynosuroides distribution along the Altamaha River estuary. Abiotic (salinity) and biotic (intra/interspecific competition) influences on Spartina growth were investigated through reciprocal transplant studies coupled with neighbor removal treatments (at salinity extremes) and experimental species removals (from a mid-salinity, mixed species area). Results from the transplant experiments indicate that high salinities negatively affected S. cynosuroides growth more than S. alterniflora (i.e., 20% S. cynosuroides survival vs. 80% S. alterniflora survival, etc.). However, both plants showed evidence of competitive effects. The presence of neighbors increased S. cynosuroides growth (i.e. avg. height with neighbors was 1.5(±0.5) m vs. 0.85(±0) m without neighbors in the high salinity zone, 1.45(±0.73) m with neighbors vs. 0.97(±0.59) m without neighbors in low salinity zone) indicating the possibility of facilitation, whereas S. alterniflora performed poorly with neighbors present (i.e., avg. height with neighbors was 0.8(± 0.72) m vs. 1.2(±0.75) m without neighbors in high salinity zone, 0.3(± 0.45) m with neighbors vs. 0.69(± 0.14) m without neighbors in low salinity zone), indicating a possible competitive effect. We interpret these results to suggest that physiological tolerance to high salinity is the primary control of species distribution but that competitive interactions are important at lower salinities. These results provide support for the extension of the stress tolerance/competition paradigm along the length of an estuary.
Key words: competition, salinity, spartina, zonation