Natural growth lines in sea urchin (Heliocidaris erythrogramma) ossicles

Brief description

Sea urchin tagged using tetracycline display visible marks in jaw elements and test plates that can be used to determine growth and subsequently an individuals age. Natural growth lines in the same structures can be used to determine age if natural lines are deposited at a consistent rates independent of age. Sea urchins were tagged using tetracycline and age determined from both fitted growth models and the number of bands deposited. Rates of natural line deposition were also quantified.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Approximately 400 individual urchins were chemically tagged at each of three sites in the Mercury Passage, Tasmania. At each site all sea urchins from an experimental plot measuring approximately 10m x 6m were collected for tagging. Sites were at Four Mile Point (42o 37'S, 148o 01'E), Chinamans Bay (42o 40'S, 148o 02' E) and Lords Bluff (42o 31'S, 147o 59'E), and experimental plots were located on the 5m depth contour. The test diameter of each urchin was measured, and individuals received a standard dose of tetracycline for tagging. Chemically tagged sea urchins were returned to experimental plots. Two samples of tagged sea urchins were later recovered to determine the deposition rate of growth lines, 12 and 24 months post-tagging. Sample preparation: Prior to dissection the test diameter of the urchin was measured. On dissection, half of the test and the entire Aristotle's lantern were placed into a solution of 5% sodium hypochlorite. The calcified material remaining after 24 hours was rinsed thoroughly with freshwater before being air-dried for 48 hours. Four separate ossicles were selected from each individual sea urchin. Three plates were selected from the interambulacral column for preparation, viz. from the oral end, mid-axis and aboral end along with one demipyramid. The mid-axis plate is located at the maximum radius of the test curvature. The oral plate was located by measuring the mid-point between the oral nerve complex and the mid-axis plate and the aboral plate located mid way between the mid-axis plate and the genital plate. For further details on sample preparation, selection and growth measurement please contact the researcher.

Notes

Credit
Australian Research Council (ARC)

Purpose
Determine if natural growth lines in sea urchin jaws and test plates could be used to accurately determine age.