Black Mantle Tissue of Endolithic Mussels (Leiosolenus spp.) Is Cloaking Borehole Orifices in Caribbean Reef Corals

Abstract

Bioerosion caused by boring mussels (Mytilidae: Lithophaginae) can negatively impact coral reef health. During biodiversity surveys of coral-associated fauna in Curaçao (southern Caribbean), morphological variation in mussel boreholes was studied. Borings were found in 22 coral species, 12 of which represented new host records. Dead corals usually showed twin siphon openings, for each mussel shaped like a figure of eight, which were lined with a calcareous sheath and protruded as tubes from the substrate surface. Most openings surrounded by live coral tissue were deeper and funnel-shaped, with outlines resembling dumbbells, keyholes, ovals or irregular ink blotches. The boreholes appeared to contain black siphon and mantle tissue of the mussel. Because of the black color and the hidden borehole opening in live host corals, the mantle tissue appeared to mimic dark, empty holes, while they were actually cloaking live coral tissue around the hole, which is a new discovery. By illustrating the morphological range of borehole orifices, we aim to facilitate the easy detection of boring mussels for future research.

Stony Corals and Their Associated Fauna Residing in Marine Lakes under Extreme Environmental Conditions

“…Clusters of the box mussel bivalve, Septifer bilocularis (family Mytilidae), were present in high densities over the upper surface of massive coral colonies and inside crevices (Figure 6a-c). Boring mussels of the genus Leiosolenus (previously also known as Lithophaga) of the same family lived inside massive Porites corals, showing their characteristic orifices [46][47][48][49] scattered over their host's surface (Figure 6d). The shell ribs of Septifer bilocularis resemble those of Brachidontes spp., which were also found to be abundant in the lakes but not in association with corals [22].…”