Rate of spiculogenesis in some common Mediterranean Calcispongiae: A tetracycline and ⁴⁵Ca⁺⁺ labelling study

Abstract

Calcareous spicule formation was studied using tetracycline and ⁴⁵Ca⁺⁺ tagging in Clathrina cerebrum (Haeckel), Ascandra falcata Haeckel and Sycon ciliatum (Fabricius) (Porifera: Calcispongiae). The percentage of fluorescent spicules 24 h after the start of the experiment was similar in C. cerebrum and A. falcata (about 13% of the whole spicular population), while no fluorescence occurred in S. ciliatum. Results from ⁴⁵Ca⁺⁺ labelling experiments were similar in C. cerebrum and S. ciliatum. Estimated rates of spicule production by tetracycline labelling (30 mg/g/day and 34 mg/g/day for Clathrina and Ascandra, respectively) were about four times greater than those by ⁴⁵Ca⁺⁺ tagging (8.2 mg/g/day and 8.1 mg/g/day for Clathrina and Sycon, respectively). Our data show that about 1–3% of sponge calcite in the three species examined reforms in 24 h, suggesting that a constant deposition rate of from one to three months is needed for a complete turnover of the total spicular population.

Key words:

• Biocalcification
• Spiculogenesis
• Tetracycline
• ⁴⁵Ca⁺⁺