Ancient shipwreck reveals 'ecological memory' of reefs

An ancient warship sunk in 241 BCE has revealed how aquatic animals construct a home.

The Battle of the Aegates Islands laid the path for the domination of the Roman Empire in antiquity, but also left the seabed near Sicily littered with the remains of sunken ships.

Though many human lives were lost in the conflict, scientist have now found that these ships provide a record of the animals which have lived under the sea during this time. In total, 114 different invertebrate species were found living together on the ram of a Carthaginian warship.

Lead author Dr Maria Flavia Gravina from the University of Rome, says, 'Younger shipwrecks typically host a less diverse community than their environment, mainly species with a long larval stage which can disperse far.

'By comparison, our ram is much more representative of the natural habitat: it hosted a diverse community, including species with long and short larval stages; with sexual and asexual reproduction; and with sessile and motile adults, who live in colonies or alone.

'We have thus shown that very old shipwrecks, such as our ram, can act as a novel kind of sampling tool for scientists, which effectively act as an "ecological memory" of colonisation.'

The research, led by a group of Italian institutes, was published in the journal Frontiers in Marine Science.

When history meets biology

Since humanity first took to the oceans, there have been shipwrecks. The cultural organisation UNESCO estimates that there are around three million sunken boats lying on the seabed, in addition to other manmade craft such as planes.

There are a variety of reasons for why they end up on the sea floor. For instance, many vessels from the Spanish Armada sank in stormy weather, while the Titanic famously collided with an iceberg.

Vessels can also be sunk deliberately. Ships can be scuttled to provide the beginnings of artificial reefs, but may also be sunk for military purposes, such as those of the German fleet at Scapa Flow in the aftermath of World War One.

The ships sunk during the Battle of the Aegates Islands, however, came under attack during the First Punic War. Both the Roman Empire and its foe Carthage, an ancient state in north Africa, were equipped with bronze rams on the front of their ships which were designed to breach enemy vessels.

The battle, fought on 10 March 241BCE, was a decisive victory for the Romans and led to the end of the war. Many of the shipwrecks from the conflict were relocated by archaeologists in the mid-2000s off the coast of Sicily.

While previous studies have looked at the archaeological significance of the site, biologists wanted to use it to investigate how artificial reefs form over thousands of years.

Co-author Dr Sandra Ricci says, 'Shipwrecks are often studied to follow colonisation by marine organisms, but few studies have focused on ships that sank more than a century ago.

'Our study is the first to focus on the colonisation of a wreck over a period of more than 2,000 years.'

Archaeological allies

Sediment and layers of marine animals were encrusted onto the bronze naval ram, which was removed from the front of a Carthaginian ship.

Each animal was identified to the species level, including 58 species of mollusc such as snails and clams; 33 species of underwater worms known as polychaetes; and 23 species of colonial animals known as bryozoans.

Co-author Dr Edoardo Casoli says, 'We deduce that the primary constructors in this community are organisms such as polychaetes, bryozoans, and a few species of bivalves. Their tubes, valves, and colonies attach themselves directly to the wreck’s surface.

'Other species, especially bryozoans, act as binders where their colonies form bridges between the calcareous structures produced by the constructors. Then there are "dwellers", which aren’t attached but move freely between cavities in the superstructure.'

The species make-up of the naval ram community was then compared with the surrounding area to assess if the group of animals living on the shipwreck differed significantly.

The researchers found that the animal communities living on the ram were most comparable to deep reefs and environments known as detritic bottoms, similar to the surroundings the shipwreck was found in. While newer shipwrecks can differ significantly from their surroundings by the animals that inhabit them, this suggests that they blend in once given enough time.

The researchers now hope to find out the order in which the different animals arrived to colonise wrecks, allowing them to learn more about how these ecosystems have changed over thousands of years.