Recruitment, growth, and mortality of a living articulate brachiopod, with implications for the interpretation of survivorship curves

Abstract

An intertidal sample of 118 to 155 Terebratalia transversa on Saltspring Island, B.C., was censused in 1974, 1975, and 1976. Growth in length was a maximum of 7.8 mm per year and declined with size (age). As in fossil articulates, mortality rate was independent of age (size). Recruitment was patchy in time and space, was multi-annual or continuous, and was concentrated near conspecific adults. There were as many as 800 individuals/m2. None moved or changed orientation. Morphologic variation of Terebratalia valves is not directly controlled by the intensity of waves or currents.Paleontological survivorship curves based on size-frequency data are subject to ambiguous interpretation because two critical assumptions (direct relationship of size and age, constant population structure) are difficult to justify.