Observations on intertidal organism associations of St. Catherines Island, Georgia. 2, Morphology and distribution of Littorina irrorata (Say). American Museum novitates ; no. 2873

Abstract

"The marsh periwinkle Littorina irrorata (Say) occurs in a variety of Spartina marsh settings on St. Catherines Island, Georgia. Cohorts of L. irrorata were collected at four marsh localities and control grids were monitored over a three-week period. In addition, a fossil population was collected from a relict marsh mud. Each sample was subjected to detailed morphometric analysis using univariate, bivariate, and multivariate techniques. Adult size of L. irrorata is inversely related to population density and density, in turn, is directly proportional to the abundance of Spartina grass. Progenesis appears to be the adaptive strategy adopted for size decrease. Aperture shape exhibited the least variation and was relatively independent of translation rate, whorl expansion rate, aperture angle, and total width. larger apertural area was correlated with low marsh environemnts ('wetter' conditions). Total width of L. irrorata proved to be a better indicator of population structure than total height and should be used in the construction of survivorship curves for this species. The fossil population sample apparently refelcts substantially different growth dynamics, achieving adult size at fewer than six whorls. L. irrorata is a potentially useful tool for paleoenvironmental reconstructions. the species appears to exhibit limited lateral motility and has a strong distributional dependence upon Spartina grass. Monitoring cohorts of L. irrorata demonstrated a direct relationship between population density and short-term stability of population size"--P. [1].