Paleoecology of a Pliocene coral thicket from North Carolina: an example of temporal change in community structure and function

Abstract

A two meter stratigraphic interval within the Chowan River Formation of North Carolina contains a thicket of branching coral, Septastrea crassa (Holmes), associated with a diverse macrofaunal assemblage. The thicket modified a local shelf habitat by providing protection and feeding opportunities for certain vagrant epifaunal species. Faunal adjustments wrought by the thicket and thicket growth represent autogenic succession. Coral growth rates and preservation suggest a time span of about 100–300 years for thicket development.Bottom shoaling, associated with a eustatic regression, caused movement of a depth controlled environmental gradient during thicket growth. As the habitat changed, a plane bottom macrofaunal assemblage replaced the thicket assemblage by reordering abundances of intergradational species and introducing a few new species. Faunal density, diversity, trophic structure, and modes of life of component species were altered during replacement.Observed temporal community changes are best explained as gradual faunal adjustments along a shelf stress gradient. Short term allogenic or autogenic events may temporarily perturb gradual changes. Changes associated with thicket development are interpreted as a brief autogenic perturbation of long term community replacement.