Grotta dei Gamberi, Ustica: deep cave exploration with unicorn shrimp

The Grotta dei Gamberi, also known as Shrimp Cave, is a significant volcanic cave system located off Punta Galera on the southwest coast of Ustica, Sicily. Access to the site is typically by boat from Ustica Island dive centres, mooring near the single buoy at Punta Galera. From the surface, you descend along the reef, following its slope down to a sandy seabed where the cave entrance opens between 38 and 42 metres. This initial approach sets the stage for a deep dive, requiring careful buoyancy control from the outset.

Upon reaching the entrance, you'll find a large, inviting opening that leads into a spacious primary chamber. The cave's topography is defined by rocky ridges and lava tongues, remnants of its volcanic origin. As you penetrate deeper, the ambient light from the entrance gradually diminishes, replaced by the beam of your dive light. This transition highlights the delicate microfauna and organisms that thrive in this low-light environment, clinging to the cave walls and ceiling.

The main feature of the Grotta dei Gamberi is its extensive horizontal structure, stretching for approximately 320 metres. Beyond the initial chamber, the cave narrows into a corridor that begins to ascend inside the cliff. This internal profile rises from around 40 metres at the entrance to an exit point near 24 metres, continuing further up to about 13 metres depth. Navigating this ascending corridor requires precise trim and propulsion techniques to avoid disturbing the delicate cave floor and walls.

The site earns its name from the dense colonies of unicorn shrimp (Parapandalus) that carpet the ceiling and walls throughout the cave. As your light sweeps across these surfaces, their eyes reflect back, creating a shimmering, almost surreal display. Observing these shrimp in their natural habitat, you'll notice their constant activity, a testament to the rich, albeit specialized, ecosystem within the cave. This unique visual is a primary draw for divers willing to undertake the challenge.

Beyond the shrimp, the cave system and its surrounding reef host other marine life adapted to these conditions. Within the cave, you might encounter hake, conger eels, and various crabs and lobsters tucked into crevices. Moray eels are also resident, often found in the darker recesses. Outside the cave, along the rich reef of Punta Galera, barracuda can be seen, adding to the diversity of the dive.

The ambiance inside the Grotta dei Gamberi is distinct from an open reef dive. The water is often calmer, and the silence more profound, creating an intimate exploration experience. While large pelagic species are less common inside, the focus shifts to the intricate details of the cave's inhabitants and formations. Every corner and anfratuosity holds the potential for discovery, rewarding patience and meticulous observation.

Visibility within the cave system is generally good, often ranging from 20 to 30 metres or more, which is crucial for safe cave penetration. While currents are not a primary hazard, they can be variable. Reports indicate generally good conditions with possible weak currents, sometimes noticeable during descent and ascent along the reef. These currents are typically not strong enough to be a defining challenge but warrant awareness, especially during the initial and final phases of the dive.