The Ecology of Terpios hoshinota in the Maldives Based on Three Decades of Observation

Abstract

Coral reefs are experiencing significant degradation caused by anthropogenic environmental changes. Sponges, such as the cyanobacteriosponge Terpios hoshinota, are becoming increasingly abundant in these ecosystems. This study examines the likelihood that T. hoshinota is invasive, identifies the types of corals that are overgrown, and investigates patterns and possible drivers of T. hoshinota outbreaks on Maldivian reefs over the past 23 years. From 1990 to 2012 reefs throughout the Maldives were surveyed using transects, photoquadrats and visual surveys. The types of corals overgrown and possible correlations between sponge prevalence and environmental variables were noted. T. hoshinota was first observed in South Malé Atoll in 1990 and has since been found in many Maldivian atolls, predominantly overgrowing massive and encrusting corals. Both large and small blooms of the sponge have been transient, possibly periodic, and increased in magnitude after 1998. Both corals and T. hoshinota exhibit boom-bust population ecologies. For corals vulnerable to bleaching, these cycles are relatively predictable and largely driven by environmental factors like sea surface temperature (SST) (Morais et al. 2021). In contrast, the ecology of T. hoshinota is poorly understood and apparently shaped by stochastic environmental factors. Interactions between the sponge and corals seem to be influenced by the effects of environmental changes on the competitive balance between the two. If current trends continue, the survival of both organisms may be at risk as the degradation of reef structures accelerates.