December 4, 2021: Rock Pen
Image courtesy of NOAA Ocean Exploration, Mountains in the Deep: Exploring the Central Pacific Basin. Download larger version (jpg, 1.9 MB).
A relatively recent discovery is that some sea pens (Pennatulacea) live on hard bottoms. These “rock pens” use their peduncle, or stalk, like a suction cup, as shown on this colony at ~2,200 meters (~7,220 feet) depth on the Pacific’s North Manihiki Plateau.
As sessile fauna, octocorals such as sea pens live primarily attached and fixed in place in their habitat, meaning that they need food to come to them and are generally considered suspension feeders. Among the octocorals, biodiversity is greatest where the seafloor is dominated by rock that has mostly been swept clear of sediment. The exposed rock suggests that water flow in the area is strong enough to sweep settling sediment particles away and also deliver plenty of food.
From: Stuck to Rock and Anchored in Mud.