Effect of plant-bioturbation interaction on tidal creek growth in two contrasting saltmarsh habitats

MAURICIO ESCAPA; GERARDO PERILLO; OSCAR IRIBARNE

Bahía Blanca, Argentina

Congreso; ECSA 44. Science and Management of Estuaries and Coasts: A tale of two hemispheres.; 2008

Distribucin y efectos ecolgicos de la ostra introducida Crassostrea gigas en Bahia Anegada <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> There is strong evidence about the role of saltmarshes as protectors of the coastline, and a high proportion of the saltmarsh loss may be due to bioturbation activity that destabilizes sediments. Using field measurements and experiments, we investigated the effect of the Southwest Atlantic burrowing crab Neohelice granulata on the inland growth of tidal creeks in contrasting saltmarsh habitats (Bahía Blanca Estuary). This crab species inhabits both Sarcocornia perennis-dominated marshes and Spartina alterniflora marshes. Crab activity in relation with tidal creek growth, crab effect on sediments, plant biomass and architecture, and sediment deposition rates were evaluated in both types marshes. Bioturbation activity by this crab changed sediment physical parameters, as penetrability, water content, and shear strength; which are related to sediment erodability in both marshes. There was a positive relationship between crab activity and creek growth rates for Sarcocornia saltmarshes, and no significant relationship was found between those variables in Spartina marshes. Field experiments show that bioturbation by N. granulata and their burrows enhance growth rates of tidal creeks, promoting marsh erosion on Sarcocornia marshes but crab presence did not affect growth rates of creeks in Spartina marshes. When crabs were present, these creeks grew faster than creeks where crabs were excluded. Plant biomass was higher in Spartina marshes than Sarcocornia marshes during the year; consequently, sediment deposition rates were higher in Spartina marshes than in Sarcocornia dominated marshes. The implication is that bioturbation effects on creek growth may produce contrasting outcomes depending on the habitat structure.