Modelling somatic growth in the sea urchin Evechinus chloroticus (Echinoidea: Echinometridae)
Abstract
Somatic growth was examined in two populations of the sea urchin Evechinus chloroticus (Valenciennes). Growth was quantified for smaller urchins (<10 mm test diameter (TD)) through laboratory rearing and in situ airlift sampling of newly settled juvenile cohorts, and for larger individuals (>10 mm TD) by calcein tagging and recapture. Newly settled urchins grew to a mean size at 1 year of 8.05 mm TD in the laboratory and an estimated 10.5 mm TD in the field. Growth of newly settled urchins appeared to be biphasic with a period of slow growth (0–200 days post-settlement), followed by accelerated growth. Larger, calcein tagged individuals were recaptured 1 year after tagging and their growth modelled using three asymptotic growth functions (Brody-Bertalanffy, Richards and Jolicoeur) and one non-asymptotic function (Tanaka). A second sample of tagged urchins was recovered from one of the sites 3.9 years after the initial tagging. Evaluation of each growth model was made using (1) sum of the squares residual values of the difference equation regressions for each growth function (2) an examination of the regression residuals (3) a comparison of the predicted versus observed size at age at 1 year for E. chloroticus sampled in Doubtful Sound, and (4) a comparison of the predicted growth of urchins over 3.9 years, with the observed growth in the urchins recovered 3.9 years post-tagging. The sample taken 3.9 years after tagging also allowed us to examine whether growth is asymptotic in the larger size classes. While growth does not appear to be be asymptotic, we found the Richards function best described growth in E. chloroticus overall. Using this model, the test diameters of individuals at ages 1 to 6 years are about 10, 25, 40, 55, 65 and 72 mm TD, respectively.
- Publication:
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Journal of Experimental Marine Biology and Ecology
- Pub Date:
- January 2000
- DOI:
- 10.1016/S0022-0981(99)00107-0
- Bibcode:
- 2000JEMBE.243...17L
- Keywords:
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- Growth;
- Sea urchin;
- Echinoid;
- Evechinus chloroticus