Boring activity of the sponge Cliothosa delitrix (Pang, 1973) (Clionaidae, Clionaida) in thermoresistant corals and the state of the art of the order Clionaida in Ceará

Abstract

Cliothosa delitrix, a bioeroding demosponge of the family Clionaidae, stands out on reefs due to its high bioerosion rates in coral colonies, particularly under environmental stress conditions. This behavior makes it an efficient competitor in these environments, as bioeroding sponges erode the calcareous substrate. This process may be intensifying as a result of global climate change, contributing to the ongoing degradation of coral reefs. In this context, this study aligns with Sustainable Development Goal (SDG) 14, which aims to conserve and sustainably use the oceans. The general objective of this study was to conduct the first ecological investigation of the developmental stages of C. delitrix and its occupation of colonies of the stress-tolerant coral Siderastrea stellata, comparing bleached and healthy individuals at the Pedra da Risca do Meio Marine State Park (PEMPRIM), as well as to record and describe species of the order Clionaida along the Southwestern Equatorial Atlantic coast (Ceará, Brazil). Specimens were collected through active intertidal searches and scuba diving along the Ceará coast and at PEMPRIM (15–30 m depth). After collection, organisms were preserved in 80% ethanol and identified in the laboratory based on spicule and skeletal preparations. Ecological data on C. delitrix were collected between March and July 2024, during the fourth global coral bleaching event. We obtained 50 × 50 cm photoquadrats along 20 m linear transects, yielding a total of 40 images per dive site. Each individual and its developmental stage were quantified, and occupied area (cm²) on coral colonies was estimated. Results indicate the presence of C. delitrix boring into both healthy and bleached coral colonies. Of the 347 coral colonies surveyed, ~52% were bleached and 48% showed no signs of bleaching. Among bleached colonies, 37.99% were bored by the sponge, whereas only 2.98% of non-bleached colonies showed bioerosion, suggesting greater vulnerability to C. delitrix colonization following thermal stress and mass bleaching events. No significant correlation was found between sponge boring and depth, indicating adaptation across depth ranges and highlighting coral availability and stress condition (i.e., bleaching) as the most important drivers of bioerosion. Additionally, five species of Clionaida were identified along the Ceará coast, including the first records for the Southwestern Equatorial Atlantic of Cliothosa delitrix and Cliona carteri (Clionaidae), Spirastrella hartmani (Spirastrellidae), and Placospongia giseleae (Placospongiidae), and confirmation of the Cliona celata species complex. These findings expand regional taxonomic knowledge and characterize the spatial occupation, developmental stages, and possible preference of C. delitrix for the massive coral Siderastrea stellata with higher boring rates in bleached colonies. The dissertation will be presented in two chapters: the first on the boring activity of the sponge Cliothosa delitrix, and the second on the state of the art of the order Clionaida in Ceará.