Differences in growth rates of the sea urchin Echinocardium cordatum as estimated by the parameter w of the von Bertalanffy equation applied to skeletal rings

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Abstract
Initial observations on the echinoderm E. cordatum collected in the southern North Sea indicated that the maximum attainable size for this species differed in the different substrate sampled. This suggested either a difference in longevity or in growth rates. A method of aging E. cordatum is presented which also allows incremental annual growth of an individual to be calculated. The parameter .omega. derived from the parameters k and L.infin. of the von Bertalanffy growth model, was used to compare the growth rate of E. cordatum at different sites. Analysis of approximately 2000 specimens collected from different points along a north-south transect showed an increasing rate of growth from north to south. Maximum size of the organisms also increased in the same direction. No differences in longevity were observed. The causative factors are still speculative at this time. A number of physical parameters which form gradients along the transect provide several interesting possibilities for future investigation. The most promising of these is bottom temperature. The highest rate of growth for this organism occurs in sediments containing the lowest amounts of organic matter and biomass. This poses interesting questions regarding its food and feeding habits.

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