Scientific divers studying the wreck of the Italian hospital ship Po in Albania have found a densely colonised artificial reef that sustains varied marine life and alters sediments on the surrounding seabed.
Digitally reconstructed from the original historical photo of the Hospital Ship “Po” on the right
More than eight decades after sinking in Albania's Vlora Bay, the wreck of the Italian hospital ship Po has become both an ecological habitat and a physical influence on the surrounding seabed.
A new study has combined scientific diving, sonar surveys, sediment sampling and 3D photogrammetry to examine how the 135m wreck interacts with its surroundings. Researchers found extensive biological colonisation across its surfaces, and the structure appears to influence nearby currents and sediment formation.
The wreck will already be familiar to some X-Ray Mag readers. In issue #83 of X-Ray Mag, Cesare Balzi documented an IANTD expedition to Po, combining its wartime history with a first-hand account of exploring the remarkably well-preserved wreck.
Read X-Ray Mag's 2018 feature: Italian Hospital Ship Po.
The new research returns to the same wreck from a different perspective. Rather than concentrating primarily on its history and exploration, scientists have examined how a ship that has spent 85 years underwater is becoming integrated into—and changing—the marine environment around it.
A living wreck
Po rests upright at 33 to 37m on a gently sloping seabed within Albania's Karaburun-Sazan Marine Protected Area.
Between June 2022 and September 2024, researchers conducted 32 scientific scuba dives as part of a multidisciplinary survey. Biological observations were combined with high-definition multibeam and side-scan sonar, sediment sampling and Structure-from-Motion photogrammetry. Thousands of underwater photographs were used to build detailed 3D representations of the wreck.
More than 80 per cent of the accessible hard surfaces were colonised in the surveyed areas. Researchers identified a varied community of sponges, cnidarians, bryozoans, molluscs, tunicates and other organisms, together with 28 fish species recorded around the wreck.
The bow supported a particularly diverse and structurally complex community. Because it is more exposed to prevailing currents than other parts of the wreck, the researchers suggest that water movement may be one factor forming the different biological communities found across the ship.
They also made some unusual observations. The team recorded the invasive lionfish, Pterois miles, evidence of squid spawning and a sighting of the critically endangered Mediterranean monk seal (Monachus monachus). The researchers suggest the wreck could occasionally serve as a feeding area for the seal, although a single observation is insufficient to establish regular use.
Reshaping the seabed
The wreck does more than provide a hard surface for marine life. Sonar surveys revealed a scour hollow reaching 2.1m below the surrounding seabed on the upstream side of the wreck. Downstream, a depositional feature extends for approximately 45m.
Sediment immediately around the wreck also differs from the surrounding seabed. Fine silt and clay occur close to the structure, in contrast to the predominantly medium sand farther away. The pattern is consistent with the wreck altering near-bottom water flow and influencing where sediment is eroded or deposited. The researchers caution, however, that the study is based on observation, and that the precise sources and movement of those sediments call for further investigation.
This physical interaction is one of the study's more interesting aspects. Rather than treating a wreck as an artificial reef on the seabed, the researchers studied it as a structure that can gradually modify the surrounding environment.
From hospital ship to artificial reef
Originally built as the passenger vessel Wien, the ship was converted into an Italian hospital ship during the Second World War. Po was sunk in Vlora Bay on the night of 14 March 1941, after being struck by a torpedo launched by a British Fairey Swordfish aircraft. The hospital ship had been ordered to remain dark that night, because illuminating it could also have revealed nearby Italian naval and merchant vessels to attacking aircraft. The British aircrew therefore did not recognise it as a hospital ship before attacking. X-Ray Mag's earlier feature examined the circumstances of the sinking in detail.
Today, the wreck is simultaneously part of Albania's underwater cultural heritage, a dive site, and part of the ecology of the country's largest marine protected area. The researchers argue that recognising these overlapping roles could help historic wrecks be considered more effectively in marine conservation and spatial planning. They have proposed preliminary ecological and geomorphological indices for describing the influence of wrecks, although these will require testing at other sites before their wider usefulness can be established.
For Po, however, the wider picture is already becoming clear. After 85 years underwater, the ship is no longer simply an object resting on the seabed. It has become part of Vlora Bay's physical and biological landscape.
