MEPS 178:79-88 (1999)  -  doi:10.3354/meps178079

Effects of the SW Atlantic burrowing crab Chasmagnathus granulata on a Spartina salt marsh

Alejandro Bortolus1,*, Oscar Iribarne2

1Becario CIC and 2Investigador CONICET, Biología (FCEyN), Universidad Nacional de Mar del Plata, CC 573 Correo Central (7600) Mar del Plata, Argentina

ABSTRACT: In this work we evaluated the effect of the burrowing crab Chasmagnathus granulata on the soil quality and on the cordgrass Spartina densiflora in a SW Atlantic coastal lagoon (Argentina, 37°32'S, 57°19'W). Soil hardness and percolation rates were higher outside the crab inhabited area than inside, and soil profiles showed 2 different strata in areas without crabs. Crabs were associated with low soil water content, a higher variability in pH, and a homogeneous distribution of organic matter. Meiofaunal abundance was lower inside the area inhabited by crabs than outside. The water content of aboveground structures of S. densiflora was lower inside the crab populated areas. Leaf survival was lower inside the area inhabited by crabs than outside. In areas with new shoots (after burning by a brush fire) crabs depleted the aboveground plant structures. A caging experiment showed that crabs decreased leaf survival by herbivory. During the experiment, substrata was covered by sediment displaced by crabs, and the area showed less soil hardness and lower percolation rates than controls. Crabs decreased water content and organic matter on upper sediment layers. Meiofaunal abundance (arachnids and insects) was higher in control plots (without crabs) than in treatment plots. A field selection experiment showed that crabs decreased survival of young stems, but did not affect old stems. All this evidence suggests that C. granulata affects cordgrass production by herbivory on new shoots, and can change the physical characteristics of the environment, which may also indirectly affect S. densiflora production. Thus, the general belief that in Spartina marshes only a small proportion of primary production is consumed in situ may not apply to SW Atlantic Spartina marshes inhabited by crabs.

KEY WORDS: Spartina · Crabs · Marsh · Herbivory · Bioturbation · Fire

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