When History meets Biology Shipwrecks as Ecological Hotspots

Underwater cultural heritage (UCH) is defined by UNESCO as “all traces of human existence having a cultural, historical or archaeological character which have been partially or totally under water, periodically or continuously, for at least 100 years”. In Malta, UCH is defined as “remains found on the seabed that are situated in the territorial waters of Malta and are at least 50 years old”.

Remains range from ancient cities and submerged harbour structures to wooden shipwrecks, crashed aircraft and shipwreck sites. In the context of an archaeological investigation, these remains are scientifically examined to identify and document a cultural resource that can inform human understanding of the past. This is done through a variety of methods including remote sensing, visual surveys, 3D documentation and excavation. From an archaeological perspective, these submerged time capsules offer an insight into our collective human history. However, from an ecological viewpoint, submerged cultural remains can act as habitats for a diverse range of marine life.

When it comes to the management of UCH, Malta has over the last three years implemented an innovative approach to public access management that encompasses both diver and virtual access. Since 2019, through Heritage Malta’s Underwater Cultural Heritage Unit (UCHU), no fewer than 20 historic underwater sites have been opened to the diving public, with many of these also virtually accessible through an online museum for UCH, accessed through the link: www.underwatermalta. org. The process of selecting sites for public access classifies the sites according to three categories – war grave, unexploded ordinance, and protected marine life. Most of the wreck sites date to the First and Second World Wars and are a direct legacy of Malta’s role during both conflicts. Many of them are also the last resting place of fallen servicemen, both Allied and Axis, and the status of ‘war grave’ is given to any site with known casualties, to be equally respected as cemeteries on land. The presence of unexploded ordinance also directly relates to this wartime legacy, and the status of protected marine life is given to those sites colonised by species that are known to be endangered or ecologically important. All three of these categories contribute to Heritage Malta’s policy of “look, but don’t touch” with wreck penetration or disturbance actively discouraged. This article will focus on the category of marine life, and more specifically the WreckLife project that was initiated in 2022.

The aim of WreckLife is to bridge a significant knowledge gap. At present, there is no information available on the species associated with historic wrecks, located at depths beyond those accessible by recreational divers. The element of depth is an important consideration, since all the historic wrecks open to the public are beyond recreational diving limits, starting at 55m and extending to 115m. Studies tend to focus on either the archaeological value of a site, or on the encrustations of marine species on individual cultural objects, such as amphorae. However, shipwrecks have rarely been studied as artificial surfaces on which benthic communities –species that live on the seabed – can grow. The wreck acts as a substitute to natural rocky reefs and the study of these communities colonising wrecks remains a significant knowledge gap, making this project a crucial baseline study for future investigations. The effect of wrecks on the surrounding environment is also poorly understood, especially when taking into consideration metal shipwrecks and the polluting potential of these sites.

Another important consideration when discussing marine life and historic wrecks is that of climate change. The oceans and seas around the world have acted as crucial buffers, or carbon sinks, absorbing approximately 25% of carbon dioxide released by human activity. As a result, oceans and seas are becoming warmer, more acidic, and less oxygen-rich, impacting marine biodiversity. The impact on the deepsea is less well understood, and changes are often not as obvious as on the surface, but may nevertheless have a profound effect. Such changes will also impact UCH, particularly on the various materials that constitute these sites. A prime example of this is the potential increase in corrosion levels on metal wrecks due to increasing water temperatures, an impact that may result in accelerated polluting events (such as oil spills). Marine species are excellent indicators of climate change, sensitive to these variations and often studied and tracked over long periods of time. The study of legacy data through the WreckLife project and the generation of new baseline data sets, will enable Heritage Malta to better anticipate and mitigate against climate induced changes.

Large areas of the seafloor remain empty and deserted, void of any distinguishable features that would otherwise provide a hard structure on which marine organisms can settle. Many marine species spread by drifting or floating with the ocean currents as larvae or by crawling on the ocean floor. Whilst drifting, the larvae need to find a rigid structure, such as a rocky outcrop or reef, that will provide a solid surface on which to settle and grow. Almost like an isolated ‘island-oasis’ on an otherwise empty desert landscape, shipwrecks protrude from the seabed and provide a rigid structure with an assortment of surfaces made of various materials with different angles, overhangs, textures and holes. These offer many opportunities for colonising organisms to hide and shelter, as well as encouraging biological diversity. Complex communities are thus created around wrecks, which in turn develop into environments that facilitate a multitude of species, all taking advantage of the superstructure of the wreck.

Effectively, shipwrecks fulfil a similar role to natural habitats like coral reefs, kelp forests and rainforests, albeit artificially, by enabling a wide range of marine life to congregate in one place. With shipwrecks hosting so many different physical features, the abundance and variety of life will naturally vary on each site. This is largely due to the resting place of wrecks varying in depth, temperature, available light, current movement, surrounding seabed morphology, and other environmental drivers present around each site.

Considering their location in the centre of the Mediterranean, it comes as no surprise that the Maltese Islands proved to be a strategic position for seafaring people and nations. This allowed Malta to become a maritime hub with a seafaring history dating back to approximately 5500BC, when its first inhabitants arrived on rafts or simple vessels. However, the first group to start using Malta as an outpost for trade and other shipping activities was the Phoenicians, who played a large part in establishing the archipelago’s importance as a maritime hub (Gambin 2003).

Recent conflicts, such as the first and second World Wars saw the loss of numerous ships and aircraft off the Maltese Islands. Vessels were sunk by sea mines and torpedo strikes or scuttled due to major damage sustained from the latter and air raids. Many of these wrecks now lie concentrated within a