Densities of cyanobacterial cells, spicules, and particles in the coral-killing sponge Terpios hoshinota in Sesoko Island, Okinawa, Japan

Abstract

The coral-killing sponge, Terpios hoshinota, has great potential to cover corals and threaten coral reefs. This sponge has numerous endosymbiotic cyanobacterial cells, silicate spicules in the tissue, and particles on the tissue surface, which could have an important role in the growth and defense of the sponge. However, little is known about the morphological traits of these components. Here we report the estimated density measurements of cyanobacteria by grinding the coral branch covered by the sponge without sponge tissue remains. Density was estimated to be 1.2 ×107 cells cm−2. We also obtained the densities for the spicules and particles which were 4.7×105 cm−2 and 1.3×106 cm−2, respectively. The spicule length of the Sesoko sample was shorter than those reported in previous studies. Size frequency distribution of the particles was measured for the first time, showing that the sponge selected silt-size particles with a mean size of 22.3 µm. We conclude that this study provides basic information on measuring the important components of T. hoshinota and is useful for comparing the measurements of those components in other coral reefs overgrown by this coral-killing sponge.