Orange Sea Grapes

Stolonica socialis

Stolonica socialis is a colonial tunicate that forms small clusters of zooids, each reaching up to 2 cm in height. These zooids are typically orange but can also appear yellow or pale brown. The smooth outer surface of the zooids is distinctive, as sand does not adhere to them, while the mat of stolons may collect sand. Stolonica socialis is found in the northeastern Atlantic Ocean, particularly in the Irish Sea and the English Channel, where it inhabits rocky seabeds at depths ranging from 5 to 35 meters. It prefers shaded areas on rocks, boulders, and overhangs, often forming large populations that can spread across the substrate. As a filter feeder, Stolonica socialis draws in water through an inhalent siphon, filtering out edible particles before expelling the water through an exhalent siphon. The colony grows by extending stolons across the rock surface and budding new zooids. In winter, dormant orange-red buds can be observed, which develop into zooids in spring. This species reproduces sexually, releasing eggs and sperm into the water column during adverse conditions. The presence of secondary metabolites called stolonoxides may help prevent the colonization of other organisms on its surface. Encounters with Stolonica socialis during dives can be interesting due to its unique coloration and colonial structure. Divers may find large sheets of these tunicates covering rocky surfaces, providing a visual contrast against the backdrop of the seabed. While not currently evaluated for conservation status, its presence in various dive sites suggests it is relatively common in its habitat.