Enviro-Days 1997 The effect of periwinkle grazing on saltmarsh cordgrass growth and reproduction: evidence for compensatory growth

Brian Reed Silliman and Jay Zieman

Much evidence in the literature has pointed to the potential importance of grazing on saltmarsh cord grass, Spartina alterniflora, by the gulf periwinkle, Littoraria irrorata. Many studies have investigated the overall consumption of Spartina production by Littoraria and the palatability of varying stages of senescing cord grass leaves to these prosobranch molluscs. None, however, have determined whether Littoraria grazing is deleterious, inconsequential, or stimulatory to Spartina production. This experiment is unique in that it is the first to investigate Spartina’s growth response to periwinkle herbivory. The grazing effect of Littoraria on Spartina growth and reproduction was monitored from May, 1996 through October, 1996 at both old and young marsh sites at the Virginia Coast Reserve/Long Term Ecological Research Center on Hog Island, VA. Nine-1 m2 enclosure pens were placed at equal elevations along the interface of medium and tall-form Spartina at each of the two sites. Treatments for the pens were: 1) three times the natural occurring density of Littoraria (3x pens), 2) the naturally occurring density of Littoraria (control pens), and 3) zero Littoraria (zero pens). Preliminary results from the Old Marsh site suggest that Littoraria grazing at natural occurring densities stimulates early and mid-season Spartina production.

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