Monthly progression rates of the coral-killing sponge Terpios hoshinota in Sesoko Island, Okinawa, Japan

Abstract

Terpios hoshinota is a black, encrusting sponge that hosts numerous symbiotic cyanobacteria in its tissues. The sponge often overgrows live scleractinian corals, thereby causing widespread and accelerated coral loss. However, our understanding of how subtropical waters influence the seasonal change in the progression rate of the sponge is poor. To elucidate the progression dynamics over a year, we obtained monthly measurements of linear progression of T. hoshinota (mm month−1) on the branching coral Montipora digitata in the subtropical waters of Sesoko Island, Okinawa, Japan from 2019 to 2020. The progression rate of T. hoshinota varied monthly throughout the year. The progression rates were the highest in summer (July, August, and October) with a mean value of 66 mm month−1, except in September, when strong typhoons came close to Okinawa and the progression rate decreased temporarily. The progression rates were the lowest in February 2020, at 9 mm month−1. The mean annual linear progression rate was estimated to be 28 mm month−1. Therefore, the progression dynamics of T. hoshinota could be linked to their growth mechanisms in relation to the seasonal changes in subtropical waters.