ICMM - International Council on Mining & Metals

CASE STUDY

Monitoring marine species diversity

Background

Minera Escondida Ltda. (MEL), owner of the world's largest producing copper mine, began operations in December 1990. The mine site is in northern Chile's Atacama Desert, 160 kilometres southeast of the port city of Antofagasta, at 3100 metres above sea level. As part of its operations, MEL produces and transports copper concentrates through a 170 kilometre slurry pipe to the seaside at Punta Coloso at the southern end of the Bay of Antofagasta, 14 kilometres south of the city itself.

In 1990, MEL built a copper concentrate filtering plant and port facility for copper concentrates. The seaside industrial facilities were built at Punta Coloso, on approximately 21 hectares, with a fenced coastal marine concession and a coastline of some 3 kilometres. This concession operates as a preserved coastal area and is one of the few located in northern Chile. In light of that, for the 14 years since the mine opened MEL has run a marine environmental monitoring programme that has focused on the state of coastal ecosystems in and around Punta Coloso, in particular evaluating marine species diversity (macroalgae, invertebrates and fish). A key aspect of MEL’s approach to its research on marine coastal systems in Chile has been publication of the results the company has obtained, which adds credibility and transparency to industrial operations.

Watching a Unique Species

To monitor the condition of the coastal ecosystems, MEL compared conditions inside the Punta Coloso Marine Reserve, which is closed to the public, with conditions in adjacent coastal intertidal and subtidal areas, which are open to the public and to fishing activities, such as intertidal food-gathering and nearshore skin diving. Both of these resource-extracting activities are widely practised in the Bay of Antofagasta.

Researchers focused on the barrel-shaped ascidian (sea squirt) Pyura praeputialis as a biological indicator of conditions in the area. P. praeputialis is an autogenic bioengineer’ that creates dense and extensive masses in the mid-low rocky intertidal fringes and the shallow subtidal area, down to about 5 metres. Autogenic bioengineers are species that generate long-lasting structures that modify the resources used by associated species – thus they influence key ecological or physiological mechanisms, maintaining high levels of species diversity.

The species was selected due to its biological characteristics: it is abundant, dominant, locally fished for bait and food, an autogenic ecosystem bioengineer, an alien species and unique to the Bay of Antofagasta. P. praeputialis was introduced to the bay probably a few hundred years ago from Australia. Apart from this bay, plus approximately 8 kilometres of coastline south of the bay, the species is not found in other localities along the coast of Chile or South America. From the Chilean marine species diversity point of view, therefore, P. praeputialis is a unique species.

Evidence of High Species DiversityP. praeputialis, researchers found that inside the rocky shore of the Bay of Antofagasta, at the lower mid-intertidal belt, this ascidian harbours 116 species of macro-invertebrates and algae – both inside its matrices and attached to the ascidians themselves. In contrast, in sites outside the Bay at the same tidal level, the number of macro-invertebrates and algae reaches only 66 species.

Thus the monitoring programme led researchers to conclude that matrices of this ascidian increased species richness at intertidal local and seascape scales by providing novel habitats that are used by mobile macro-invertebrates that are free to move about and that otherwise would be excluded from this particular tidal level. Furthermore, it has been found that P. praeputialis provides nursery areas for juveniles – offering protection against predation for a large class of exploited molluscs, such as the gastropod ‘loco’ and keyhole limpets, and crustaceans, such as crabs. Another conclusion of the monitoring is that MEL’s industrial activities in Punta Coloso have not had negative impacts on populations of P. praeputialis or rocky and shallow subtidal marine communities.