Variable Loggerhead Sponge

Overview

The Variable Loggerhead Sponge (Ircinia variabilis) is a common marine sponge known for its highly adaptable growth forms and distinct, rugged texture. Often called the "stinker sponge" due to its strong odor when removed from the water, this species plays an important role in benthic ecosystems by providing refuge for various small invertebrates.

Distribution & habitat

This species is primarily found throughout the Mediterranean Sea and the eastern Atlantic, including the Azores, Canary Islands, Cape Verde, and the Gulf of Guinea. It typically inhabits well-lit, shallow, and agitated rocky environments, often settling on the upper surfaces of rocks rather than vertical or overhanging faces.

Appearance

As its name suggests, the Variable Loggerhead Sponge exhibits a wide range of shapes, appearing as massive, globose, encrusting, or even branched structures. Its surface is characteristically wrinkled and covered in numerous conules—small, conical projections—which may be connected by ridges. The sponge features a few large, slightly raised oscules (exhalant openings) often located at the top of its lobes. Its coloration is equally diverse, ranging from greenish and brownish to purplish-brown, often influenced by symbiotic cyanobacteria. Despite its soft appearance, the sponge is remarkably tough and difficult to tear, thanks to a dense internal network of spongin fibers and fine filaments.

Biology & behavior

Ircinia variabilis is a filter feeder that consumes plankton and microorganisms from the water column. It reproduces both sexually, releasing larvae that settle on the substrate, and asexually through fragmentation. It is known to host various small organisms within its structure and can help stabilize the substrate when growing in an encrusting form.