Observations on intertidal organism associations of St. Catherines Island, Georgia. 1, General description and paleoecological implications. Bulletin of the AMNH ; v. 159, article 3

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New York : American Museum of Natural History
"Intertidal environments of St. Catherines Island, Georgia are diverse and include exposed sand beaches, sandy tidal flats, relict salt marsh deposits (mud and peat) on exposed beaches, and salt marsh complexes. Nine localities from the northern half of St. Catherines Island were selected for study because they displayed a wide variety of intertidal habitats and organism associations. No attempt was made to describe the entire spectrum of intertidal associations on St. Catherines Island. The bulk of study was made on the relict salt marsh deposits. Besides representing unique modern habitats for infaunal and epifaunal bivalve-dominated associations, the salt marsh deposits gave us valuable paleoecological insights. The organism groupings recognized in the present study are associations in the sense of Kauffman and Scott (1976), but communities in the usage of most workers. One relict mud occurrence contained an assemblage of six distinct associations. The fidelity of replication of these associations in the fossil record depends, in part, upon the steepness of the intertidal environmental stress gradients and the resultant spatial and temporal environmental heterogeneity. The infaunal bivalves of the relict muds showed expected trends of size distribution with depth, the larger individuals occupying the greater depths. It is suggested that the lateral transportation of dislodged mud clasts has an analog in the geological past in the occurrence of 'exotic' fossiliferous pods and steinkerns. Association boundaries were sharp only where spatial heterogeneity was pronounced, such as within salt marsh complexes. The polychaete associations along sandy tidal flats were less clearly bounded and were often marginally intergradational. Many observations on the intertidal associations of St. Catherines Island were in disagreement with observations made on similar associations elsewhere. Contrary to the conclusions of Woodin (1976), dense infaunal bivalve populations (Petricola pholadiformis) did coexist with dense epifaunal bivalve populations (Brachidontes recurvus). Also, repeated observations of dense tube-building polychaete populations failed to show epifaunal bivalves as predominant co-occurring forms. Polychaete associations along a narrow tidal flat displayed onshore-offshore distributional trends that may have paleoecological utility in the resolution of transgression-regression sequences. Tidal creek populations of Ilynassa obsoleta have a narrower aperture relative to total height than similar populations from more open sand flats. It is suggested that this is correlated with the greater duration of intertidal exposure in the tidal creek habitat. Study of another intertidal snail, Littorina irrorata, demonstrated considerable lateral as well as vertical motility in that species"--P. 89.
p. 89-128 : ill., maps ; 26 cm.
Includes bibliographical references (p. 127-128).