Corals Used as Ballast: The Zen City Site, an 18th Century Shipwreck Found at Buenos Aires City, Argentina

By Nicolas Ciarlo, Associate Editor for Maritime Archaeology

M. WeisselDirección de Patrimonio Museos y Casco Histórico, Ministerio de Cultura, GCABA, Argentina;

R.M. Garberoglio, Laboratorio de Ecosistemas Marinos Fósiles, IDEAN, FCEN-UBA,

H. PadulaDirección de Patrimonio Museos y Casco Histórico, Ministerio de Cultura, GCABA, Argentina;

The Zen City site, found in 2008 when digging the foundations of a homonymous building complex, corresponds to the remains of an early 18th century Spanish merchant ship that sank with products from Spain at the entrance of Buenos Aires port, in Argentina.

Coral remains recovered from a 9,5 cubic meters pile of stone ballast from the site comprehend 279 items, which were preliminary catalogued as scleractinian coral skeletons. All corals have a roughly rounded shape, with maximum diameters between 3 and 30 cm (avg: 12.7 cm) and a weight between 10 and 10,000 g (avg: 637 g). These parameters are similar to other contemporary examples (Keith and Simmons, 1985; Gifford, 2014), evidencing a common selection criterion.

These samples were observed under magnifying glass (10x) and grouped in different morphotypes. Representative well-preserved specimens (n: 16) were selected, and were identified at specie level based on their morphological characteristics and using the systematic literature of the group. The scleratinian assembalge correspond to the following four species: Siderastrea radians (130), Porites astreoides (60) (Fig. 1), Orbicella annularis (49) and Pseudodiploria strigosa (11) (Fig. 2); other 29 fragments were too worn to be determined. All four species have massive/hemispheric growth habits, live in shallow waters and have a broad distribution in the Caribbean Sea. S. radians and P. astreoides also occur in West Africa islands and coasts, and the later also in Brazilian waters. Given this fact, and the common practice of reusing ballast material, makes it possible for corals to have been loaded in the Caribbean region or at some point on the route between Spain and Buenos Aires. 

Figure 1. Siderastrea radians (1), Porites asteroids (2). Photograph (2x). 

There are scarce reports of corals carried on board as a minor component of ballast, and only few of them have been identified. Two of the recorded species in the Zen City site are among the four found at a Spanish shipwreck from 1559, located in Pensacola Bay, Florida (Gifford, 2014), and all four are among those used for the construction of the San Juan de Ulúa fort, at Veracruz, Mexico (Carricart Ganivet, 1998). 

Figure 2. Orbicella annular (3), Pseudodiploria strigose (4), Photograph (2x).

On the other hand, the possibility that coral pieces were shipped to be sold at the destination port as raw material for manufacturing lime, should also be considered. Altogether, the analysis of corals recovered from this shipwreck brings new evidence to discuss the ship's itinerary.



Carricart Ganivet, J.P., 1998. Corales escleractinios, “piedra mucar” y San Juan de Ulúa, Veracruz. Ciencia y Desarrollo 141:70-73. 

Gifford, M.J., 2008. Everything is ballast: an examination of ballast related practices and ballast stones from the Emanuel Point shipwrecks. Master Thesis University of West Florida. 149 pp.

Keith, D.H., Simmons, J.J., 1985. Analysis of hull remains, ballast, and artifact distribution of a 16th-century shipwreck, Molasses Reef, British West Indies. Journal of Field Archaeology 12(4):411-424.