Plexaurella nutans

Lore & Background

Plexaurella nutans can grow to a height of over a metre, with thick cylindrical branches that occasionally fork and are often slightly clubbed at the tips. The branches have a diameter of 10 to 15 centimetres. The polyps are rather large and protrude from round, oval or slit-shaped grooves in the cup-shaped calyces in the coral skeleton. Each calyx sits on a slight mound, giving the coral a dimpled surface. When the polyps are extended, as they usually are, the coral appears fuzzy. Its color is usually pale brown, grey, or sometimes lavender.

This species is uncommon and occurs at depths down to 50 metres in the Caribbean Sea, the Bahamas, and Florida. It is typically found on isolated patch reefs or on forereef slopes.

The polyps extend their tentacles to feed on zooplankton and other small invertebrates. Food is shared with neighboring polyps via the gastrovascular cavity; in an experiment, radioactive tracer fed to a single polyp was detected in tissues up to 11 centimetres away. Plexaurella nutans is a zooxanthellate species, hosting symbiotic dinoflagellates from the genus Symbiodinium. Different species of Symbiodinium were found at different depths, and when tissues were cultured in the laboratory, other species became apparent, favored by the lab environment, suggesting they were previously undetected.

Reader's Guide

Plexaurella nutans is significant as a relatively uncommon soft coral in the Caribbean region, notable for its large size—over a meter in height—and its distinctive dimpled surface created by calyces on slight mounds. Its polyps, which are usually extended, give the coral a fuzzy appearance, and its color ranges from pale brown to grey or lavender. The species is found on isolated patch reefs or forereef slopes at depths down to 50 metres, contributing to the biodiversity of these habitats.

Its biology reveals interesting features: polyps share food through a gastrovascular cavity, with experimental evidence showing nutrient transport up to 11 centimetres from a feeding site. As a zooxanthellate coral, it relies on symbiotic dinoflagellates (Symbiodinium) for nourishment, and research indicates that different Symbiodinium species occur at different depths, with additional species emerging in laboratory cultures. This underscores the complexity of its symbiotic relationships and the potential for undetected microbial diversity within its tissues. The species thus serves as a model for studying nutrient sharing and symbiont dynamics in soft corals.