Variations in bioerosion rates of different Caribbean excavating sponge species

Student: 
Lisanne Annemarie van den Bogaart

Coral reefs are highly productive and biologically diverse marine ecosystems, providing important ecological and economic services. The 3D-structure and shape of coral reefs relies on the net accumulation of calcium carbonate (CaCO3), a function of the balance between reef construction and destruction. Bioerosion by excavating sponges contributes significantly to reef destruction, particularly in the Caribbean. Total erosion rates were quantified for six common Caribbean boring sponge species: Cliona aprica, Cliona caribbaea, Myrmekioderma rea, Siphonodictyon sp., Cliona sp.-“amber papillae”, and Cliona laticavicola. Sponges contribute to erosion both chemically and mechanically. Chemical erosion was determined from increase in alkalinity of the experimental water in a newly developed flow-through system, mechanical erosion was estimated from the amount of CaCO3 chips produced by the sponges in a long-term experiment. Bioerosion rates for these species were 1.4, 1.9, 2.0, 3.6, 4.7 and 8.0 kg CaCO3 m-2 year-1, respectively. The obtained numbers were within range of reported erosion rates and close to recorded coral calcification rates, suggesting that sponge bioerosion alone could reach critical levels in areas heavily invaded by boring sponges, resulting in net destruction of the reef. These results contribute to a better understanding of sponge bioerosion, essential for proper reef management.