Maritime archaeology and trans-oceanic trade : a case study of the Oranjemund Shipwreck Cargo, Namibia

Routine sand dredging for alluvial diamonds at Oranjemund on the southern coast of Namibia exposed remnants of a long forgotten Portuguese merchant ship believed to have wrecked in the 1530s. The rescue excavations yielded over 40 tons of cargo consisting of thousands of gold and silver coins, tons of copper and lead ingots, and large quantities of ivory together with food refuse, part of personal possessions and the superstructure of the ship. This paper discusses the cargo from the shipwreck. The varying provenances show that overland inter-and intra-regional networks fed into the maritime trade between Europe and the Indian sub-continent. As such, the wreck is a lens through which we can view what was happening on the seas as well as on land. Finally we consider wider issues raised by this discovery relating to the protection and management of such material wherever it may be found in future.

Multiple dispersal vectors drive range expansion in an invasive marine species

The establishment and subsequent spread of invasive species is widely recognised as one of the most threatening processes contributing to global biodiversity loss. This is especially true for marine and estuarine ecosystems, which have experienced significant increases in the number of invasive species with the increase in global maritime trade. Understanding the rate and mechanisms of range expansion is therefore of significant interest to ecologists and conservation managers alike. Using a combination of population genetic surveys, eDNA plankton sampling and hydrodynamic modelling we examined the patterns of introduction of the predatory Northern Pacific seastar (Asterias amurensis) and pathways of secondary spread within southeast Australia. Genetic surveys across the invasive range reveal some genetic divergence between the two main invasive regions and no evidence of ongoing gene flow; a pattern that is consistent with the establishment of the second invasive region via a human-mediated translocation event. In contrast hydrodynamic modelling combined with eDNA plankton sampling demonstrated that the establishment of range expansion populations within a region is consistent with natural larval dispersal and recruitment. Our results suggest that both anthropogenic and natural dispersal vectors have played an important role in the range expansion of this species in Australia. The multiple modes of spread combined with high levels of fecundity and a long larval duration in A. amurensis suggests it is likely to continue its range expansion and significantly impact Australian marine ecosystems.