Estimating growth parameters from growth rate data : Problems with marine sedentary invertebrates.

The time interval over which growth rates are measured modifies the observed growth rates in non-linear growth curves. Growth rates obtained from a sigmoid curve such as the logistic growth equation may appear as if they were derived from the non-sigmoid von Bertalanffy growth equation when the small stage is not represented in the hypothetical growth observation. The inflection point of a sigmoid curve may be underestimated in noninstantaneous growth rate data when they are plotted on a graph against the initial sizes. This problem is significant for marine macro-benthos, whose growth is likely to be sigmoid and initiates mostly at microscopic sizes, when the popular von Bertalanffy growth equation is fitted to the observed growth rate data. Even when the von Bertalanffy growth equation appears to represent the observed growth rates adequately, extrapolation of the equation toward the smaller stage may require an independent investigation.