Sponges

Sponges are dominant, but poorly understood, components of mesophotic coral ecosystems (MCEs). Herein, we review the current understanding of mesophotic reef sponges focusing on their biodiversity, ecology, and threats, and comparing this to shallow reef sponges. The few studies of MCEs report a large number of new species, for which their contribution to ecosystem services and our understanding of sponge biodiversity and evolution are unknown. Major threats to MCE sponges are similar to threats to deep-water sponge communities and to mesophotic corals: fishing activities, pollution, and climate change, as well as in the Caribbean, invasive lionfish predation on herbivorous fishes that can result in overgrowth of algae that smother corals and sponges. The current geographic, habitat, and sampling biases prevent a full understanding of mesophotic sponge biodiversity and their ecological roles. Future studies must include not only massive sponges, but also the rare and harder to collect encrusting sponges. It is premature to draw global patterns of diversity and distribution for mesophotic sponges, since MCEs have not been studied worldwide, and geomorphological features vary within regions, causing species distributions to be highly variable.