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At the crossroads of history and biology: shipwrecks as ecological hotspots

Written by Prof Timmy Gambin, Associate Professor of Maritime Archaeology, Department of Classics and Archaeology, University of Malta; Maja Sausmekat, Principal Officer for Maritime Archaeology, Underwater Cultural Heritage Unit, Heritage Malta; and Nick Coertze, Marine Biologist, Coordinator, Underwater Cultural Heritage Unit, Heritage Malta

If you were to stand on the breakwater that protects the entrance to Malta’s Grand Harbour and look out at sea, would you think of the multitude of shipwrecks that dot the seabed? Would you think of the tragic stories behind them or the life that is flourishing on them now? These sites, by their very nature are often out of sight and out of mind, invisible to the majority and only accessible by the few, but the sea doesn’t only create a barrier between us and underwater cultural heritage sites, it also protects and preserves them. In turn, these sites become havens of marine biodiversity, often likened to island oases on otherwise barren seabeds. This is particularly true for deep-water sites, often the only distinct feature on an otherwise barren seabed.

Standing on that breakwater and looking out at sea, underwater cultural heritage is all around you. But what exactly is underwater cultural heritage? UNESCO defines underwater cultural heritage as “all traces of human existence having a cultural, historical or archaeological character which have been partially or totally underwater, periodically or continuously, for at least 100 years”[1]. You might be thinking, why 100 years? The 100-year barriers ensured that the vast majority of cultural remains from our collective human past is protected, but it often (unintentionally) overlooks cultural remains from more recent historical events such as the Second World War, making these vulnerable to looting and destruction. In Malta this time barrier was considered too broad.

Prior to 2019 there were no specific legal provisions within Malta’s cultural heritage legislation for the protection and management of underwater heritage, leading to decades of looting and mismanagement. This all changed in 2019. Monumentally, amendments to local heritage legislation contained specific sections that saw underwater cultural heritage sites being granted the same level of attention that terrestrial sites had received for over a century and when it came to defining underwater cultural heritage, a conscious effort was made to include remains from more recent historical events. The law now states that “remains found on the seabed that are situated in the territorial waters of Malta and are at least 50 years old” [2] are considered underwater cultural heritage. Remains can range from prehistoric material and submerged harbour structures to wooden shipwrecks, crashed aircraft and warships of the First and Second World War to bottles from the mid-20th century. Whilst a beer bottle from the 1950s found on the seabed might not immediately jump out as being a cultural object, Maltese legislation does not differentiate this, and considers anything over 50 years old to form part of the island’s heritage.

A defining outcome of these changes was the creation of the Underwater Cultural Heritage Unit (UCHU) within Heritage Malta, the state agency for cultural heritage. The unit is tasked with regulating public access to underwater heritage, putting an end to decades of unregulated diving. Another question to ask at this point – is who does heritage really belong to? Here, we believe that heritage belongs to the people, and so since 2019 no fewer than 20 wreck sites have been opened to the diving public, with many of these also virtually accessible through a bespoke online museum –

The Crossroads

As we answer questions such as, "what is heritage?", and "who does it belong to?" we then come to another conundrum. Can we separate tangible heritage from the natural environment? Over time, as the purpose of these areas evolve to become ecological niches, do the species which colonise them become heritage too? We now look to WreckLife, an initiative seeking to bridge the knowledge gap that exists on marine species associated with historic wrecks.

That wrecks act as artificial reefs is no secret, with scuttling projects occurring the world over to attract marine life and divers alike. Just last year the Maltese tourism authorities scuttled the MT Hephaestus, a bunkering oil tanker that had previously foundered on the coast after a bad storm. The impact of artificial reefs goes beyond the immediate benefits to the marine environment, but ripple further outward. The socio-economic value attributed to artificial reefs on a global level run into the billions, related primarily to recreational activities and food production, becoming important sources of income for local communities. In Malta, the placement of wrecks as artificial reefs relates primarily to the island’s diving tourism. Locations and depths of scuttled wrecks are chosen with specific questions in mind, like will most divers be able to reach the wreck at this depth? What is the infrastructure like around the site? Are restrooms, shops, or restaurants available in the vicinity? All these questions factor into the decision that is eventually made on the location of an artificial wreck reef, with the full knowledge that the benefits will trickle to dive centres, dive boats, sea-related stores and indirectly also to hotels and restaurants. This is why scuttled wrecks are rarely found deeper than 30 metres, opting to cater to many divers rather than the minority that are able to dive deeper than 50 metres.

The historic wrecks located in deeper waters can also be considered artificial reefs, not intentionally scuttled but beneficial, nonetheless. Whilst artificial reefs in shallower waters have been studied, the connection between historic wrecks and species that inhabit the benthic zone – meaning the seabed – beyond 30 metres is less well understood and studied. For us this is important as almost all surviving historic wrecks around the Maltese Islands are located beyond 50 metres, and what they all have in common is the remarkable quantity of marine life present.

A new approach

As scientists study wreck sites, investigators tend to focus on either the archaeological value of the site in its many variations, or on the marine life on individual objects [3]. Rarely have we focused on combining both these elements, or why these sites are important on a broader scale – for the environment, and for the people who live and work around them. Studies focused on natural and cultural heritage in the deep seas are particularly infrequent - mostly owing to accessibility constraints [4]. Here at WreckLife, we seek to bridge this gap to understand how deep-water historic wrecks act as artificial reefs, to be considered as “islands of biological diversity.” The wreck acts as a substitute to natural rocky reefs and overhangs, imitating natural features, and transforming “into artificial reefs through colonisation by microorganisms, who establish and preserve the habitability of the built structure.” [4]

Wing section of a Ju88 aircraft lying at a depth of 55m. Note the variety of marine life, including the biofilm covering the metal structure. © John Wood/Heritage Malta

Particularly in the deep sea, vast expanses of the sea floor remain barren and desolate, lacking distinct features that could serve as a solid foundation for marine organisms to settle upon. Many marine species disperse by drifting or floating as larvae, carried along by ocean currents. During their drifting phase, these larvae rely on encountering a sturdy structure like a rocky outcrop or reef where they can anchor themselves and thrive. Instead, they encounter shipwrecks, where diverse surfaces provide abundant opportunities for colonising organisms to seek refuge, find shelter, and foster biological diversity. Complex ecosystems emerge around these shipwrecks, serving as a unique hub for biodiversity. However, the characteristics of each shipwreck site differ. Depth, temperature, light penetration, water currents, surrounding seafloor topography, and other environmental factors, contribute to variations in the abundance and variety of life colonising and thriving at each site. Having established the link between biology and history, the intention is to now dive deeper into the ecological signature of historic deep-water shipwreck sites in Malta, through the WreckLife initiative.

The other side

The dark side of the synergy between historic wrecks and marine biodiversity also warrants exploration. The impact of wrecks, particularly metal ones, on the surrounding environment remains poorly understood. More specifically, it is the polluting potential of these wrecks that raise concerns. This is especially true when it is estimated that about 1.5 million tons of shipping were lost in the Mediterranean during the Second World War [5]. The primary tragedy here remains, of course, in the massive loss of human life. However, the consequences of sinking vessels that were carrying fuel and armaments have only recently started to have a detectable impact. The structural integrity of these wrecks is weakening as a result of almost a century underwater. Eventually, the fuel currently contained within the ship’s hull will spill and the only variable is when (certainly not if). It’s also worth mentioning that oil spills can’t be treated as national problems, the sea and its currents does not differentiate between national borders. What starts in one country will almost certainly negatively affect neighbouring countries. When researching these wrecks, it’s often easy and convenient to forget that there’s a dark side. Faced with the reality, it becomes harder for heritage managers to ignore what is essentially a global problem.

Oil spills can be catastrophic ‘one-off’ events, but they can also be a gradual problem. During its diving operations on the Polish warship ORP Kujawiak (L72), UCHU personnel noted evidence for a slow but consistent oil leak. This served as a wakeup that led to the prioritisation of the polluting potential of wrecks, and today the UCHU is actively working on a desk-based assessment of all known metal wrecks in Malta’s territorial waters in order to begin ranking sites for further assessment.

Fuel on the surface of the sea over a site that is known to be leaking oil. © Maja Sausmekat/Heritage Malta

The severity of the spill will be determined by things like biofouling of the ship’s hull, damage sustained during the wrecking event, seabed conditions such as light penetration, temperature and even salinity. To date, we believe that the colonisation of wrecks by marine life has added a protective layer that acts as a form of barrier between the sea and the metal. However, this will not protect the structural integrity of the wrecks indefinitely, and as the environment around us continues to change due to climate change and its associated consequences, so too will the marine environment. The impact this will have on historic wrecks is also poorly understood. Nevertheless, climate change has the potential to affect these underwater sites in several ways:

1. Increased water temperatures: Rising global temperatures can lead to warmer waters even in the deep sea. Higher temperatures can accelerate the corrosion process, particularly on metal shipwrecks. This increased corrosion can weaken the structural integrity of the wrecks.

2. Ocean acidification: The sea acts as a carbon sink, absorbing approximately 25% of carbon dioxide in the atmosphere. As carbon dioxide levels continue to rise so too does the amount of carbon dioxide absorbed by the sea, leading to increased acidity in the seawater, a process known as ocean acidification. This can accelerate the degradation and loss of shipwrecks.

3. Changes in marine biodiversity: Climate change affects marine ecosystems. Shifts in temperature, ocean currents, and nutrient availability can alter the composition and distribution of marine species. This can indirectly impact shipwrecks by influencing the communities of organisms that inhabit and interact with these sites. Changes in biodiversity can affect the colonisation of shipwrecks by marine organisms, potentially leading to alterations in ecological processes and the preservation of the wrecks.

In these cases, marine species are valuable indicators of climate change due to their sensitivity to changes in the environment. By analysing legacy data through initiatives such as WreckLife and by generating new baseline datasets, the UCHU aims to enhance its ability to anticipate and mitigate against climate-induced changes in Malta, and beyond.

To highlight how biology and history intersect, we’ll now take a dive into two shipwrecks, each with its own biological signature and story to tell. First, let’s visit the older wreck - that of HMS Nasturtium, a British minesweeping sloop.

HMS Nasturtium

The sloop formed part of Britain’s Emergency War Programme. Mine laying at sea intensified during the First World War, both offensively and defensively. Defensive mine laying had the express aim of protecting a nation’s coastline, ports, harbours, and shipping lanes, whilst offensive mine laying concentrated on laying mines in the enemy’s waters in the hope of incapacitating the opposing fleet. Minesweeping vessels were purposefully built to counter this underwater threat and would literally sweep the sea, clearing a safe path for other vessels to follow. HMS Nasturtium formed part of the Arabis-class, the largest of the five classes of minesweeping sloops constructed. Launched in December 1915, HMS Nasturtium was based in Malta searching for submarines and mines. In April 1916, a minefield laid by the German submarine U-73 claimed several vessels, one of which was the sloop. Steaming approximately 10km off the coast of Malta, HMS Nasturtium struck a mine on her starboard side, flooding the boiler rooms and expelling a significant amount of coal causing a list to port that slowly flooded the vessel. Even though several attempts were made to tow HMS Nasturtium, the sloop ultimately sunk on 28 April 1916.

Today, the wreck lies approximately 12 nautical miles off the coast of Valletta and rests on a sandy seabed at a maximum depth of 67 metres. The site was first discovered by fishermen and is in a good state of preservation, now clothed in a colourful colonisation of sponges.

Figure 4. Sponge growth on HMS Nasturtium. © John Wood/Heritage Malta 2021

Marine sponges come in many different shapes, sizes and colours which are not only pretty to look at but also help to increase habitat complexity and diversity. Sponges are one of the simplest forms of multi-cellular animals, lacking organs and a nervous system. They feed through filtering water through their porous bodies and capture nutrients from the surrounding ocean currents. The widespread distribution of both sponges and gorgonians makes them excellent indicators of habitat health. The density of sponges on HMS Nasturtium, often also noted by visiting divers, spurred the decision to carry out a sampling experiment to begin quantifying and qualifying the marine life present on the site. To this end, in early 2021, Heritage Malta applied for a sampling permit from Malta’s Environmental Resources Authority to conclusively identify the species present. Technical divers descended to the site and collected various sponge samples, guided by specialists from the University of Malta’s Marine Biology department. These were then fixed, preserved and later analysed by taxonomic specialists from the Centre for Advanced Studies of Blanes research institute of the Spanish National Research Council.

Diver collecting sponge samples from HMS Nasturtium. © John Wood/Heritage Malta

The dominant species identified from the collected sample was identified as Aplysina cavernicola. This is a species of sponge that is native to the western Mediterranean where it typically grows in caves, with its base attaching to hard surfaces and colonies of small finger-like protrusions growing from it. HMS Nasturtium acts as that all-important substitute for the hard surface on which the species normally grows. On this wreck this species is clearly thriving. The information gathered through these exercises allows heritage managers to develop a deeper understanding of how these shipwrecks are impacting the surrounding environment, and how in turn, that environment is impacting the wreck. Of note, this species is protected both nationally and internationally. Thus, the presence of protected marine life adds another level of protection to the wreck site and vice-versa, with protected wrecks providing legally protected zones with minimal human interference.

HMS Olympus

Let’s now don our fins to focus on another historic shipwreck and delve into the case of HMS Olympus. This Royal Navy submarine played a crucial role during the Second World War as part of the "magic carpet service," which involved supplying Malta with personnel and essential supplies such as fuel, food and other necessary provisions. However, operating in the vicinity of the Maltese Islands was a dangerous exercise due to the intense bombing and underwater mine laying conducted by Axis forces. In a tragic turn of events, HMS Olympus embarked on its departure from Malta in the early hours of May 8, 1942, transporting her own crew and those of two other recently sunk submarines. Catastrophically, HMS Olympus struck a mine on her way out of the Grand Harbour, resulting in its sinking and the devastating loss of 89 servicemen. This incident still stands as the worst submarine disaster in the history of the Royal Navy. In 2011, the wreck site of HMS Olympus was located at a depth of 115 metres. Resting upright on a sandy seabed it is currently the deepest historical wreck site open to divers. The wreck remains largely intact, except for damage on the starboard side where the mine struck. The open hatch on the conning tower serves as stark and poignant reminder of the crew's efforts to escape the sinking submarine. To honour the memory of those who lost their lives, a memorial plaque was placed on the submarine by a dive team from the University of Malta in 2017, coinciding with the 75th anniversary of the loss of HMS Olympus.

Memorial plaque placed on HMS Olympus, honouring the 89 submariners who lost their lives. © Dave Gration/Heritage Malta

The marine ecological importance of HMS Olympus lies in the growth of gorgonians, and especially the rare black coral – Antipathella subpinnata - on the site. Gorgonians are colonial coral organisms with a tough, yet flexible axial skeleton covered with living tissue. The term “black coral” stems from the coral’s black skeleton. Underwater black coral is confusingly white, however as soon as it’s brought to the surface and the tissue layer dies off, it turns black. Both obtain nutrients from feeding on microscopic food particles in the water column while gorgonians can also obtain nutrients through a symbiotic relationship with marine algae. Black corals lack photosynthesizing algae, which allows them to live in deeper waters unrestricted by available light sources, growing in depths up to 600 metres - The species has a slow growth rate and longevity that allows them to live for up to a millennia, no joke! These types of corals are vital in the sense that they are biodiversity hotspots, creating complex forest-like structures that allow other species to grow and thrive. This is not the only wreck in Maltese waters with such a dense concentration of black coral, suggesting that in a world of rising sea-temperatures, ocean acidification, and increased storm frequency, submerged cultural heritage sites are providing essential opportunities for marine life to grow and flourish.

Black coral growth on HMS Olympus. © Heritage Malta

Faced with adversity brought about by challenging conditions (such as depth) as well as the threat of climate change, as managers of Malta’s underwater cultural heritage we made a strategic and largely unique decision to adopt a multi-faceted approach. We believe that combining archaeology, heritage and the environment (in its broadest sense) provides a holistic approach to dealing with issues that go beyond the site-specific. It is imperative that the synergies between natural and cultural heritage are not only observed and recorded but studied, fully understood and recognised as being inseparable – this is true for the past, the present and the future.


[1] Maarleveld, T. J., Guerin, U., Egger, B. eds. Manual for Activities directed at Underwater Cultural Heritage: Guidelines to the Annex of the UNESCO 2001 Convention. United Nations Educational, Scientific and Cultural Organization; 2013

[2] Cultural Heritage Act, Cap 445. Available at: (Accessed on 27 June 2023)

[3] Gravina MF, Casoli E, Donnarumma L, Giampaoletti J, Antonelli F, Sacco Perasso C and Ricci S. Report on the Benthic Invertebrate Community Associated with a Bronze Naval Ram from the First Punic War: A Proxy of Marine Biodiversity. Front. Mar. Sci. 2021; 8:772499. https://doi: 10.3389/fmars.2021.772499

[4] Hamdan, L.J., Hampel, J.J., Moseley, R.D. et al. Deep-sea shipwrecks represent island-like ecosystems for marine microbiomes. ISME J 2021; 15, 2883–2891.

[5] Michel, J., Etkin, D.S., Gilbert, T., Urban, R., Waldron, J., Blocksidge, C.T. Potentially polluting wrecks in marine waters. IOSC 2005: International oil spill conference. May 2005, 15-19. Accessed on 30.06.23


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