Natural and anthropogenic influences on cold-water corals of the Chilean fjords: A historical perspective using geochemical tracers

Laura Robinson, Marine Chemistry and Geochemistry

Grant Funded 2007

Despite high levels of biodiversity, endemism and its complex climate and coastal morphology, the North Patagonian fjord system in southern Chile remains one of the least explored areas of the world. Ongoing baseline surveys persistently reveal new species and unique ecosystems to be living in the fjord regions, from the inter-tidal zone, through to hundreds of meters water depth.  The fauna and flora are well adapted to living in a dynamic environment, where parameters such as nutrients, salinity and temperature fluctuate on daily, seasonal and multiyear timescales. However, changing land use and the expansion of industries such as aquaculture are causing new and increasing environmental pressures on the fjord ecosystems. In addition, climate changes are likely to have a substantial impact through processes such as glacial retreat and shifting rainfall distributions. Variations in sediment and nutrient loading, temperature or pH over and above natural variability, are poised to upset the existing delicate balance between environment and ecosystem. At present, however, the rates and spatial extents of these influences are poorly known.

One particularly striking species that has been found thriving at high densities the shallow waters of the fjords is the solitary coral Desmophyllum dianthus. However, in some areas entire dead colonies have been observed, and the exact reason for their mortality is unknown. The fragility of cold-water (often referred to as deep-sea) coral populations has received heightened media and scientific attention in recent years, but investigations are costly at the great depths (many thousands of meters) that the corals normally inhabit. This project aims to gain a unique historical perspective of the natural and anthropogenic pressures on D. dianthus by measuring chemical tracers in the skeletons of the corals themselves. High resolution trace element and isotopic analyses will be used to constrain the timing and amplitude of natural variability in the fjord waters, and changes that have happened before and since the initiation of pervasive anthropogenic influences in the region. Novel geochemical techniques will be directed towards determination of sediment loading in the fjord over the last century in corals that were collected both live and dead. Coupled with age dating of dead coral individuals, this data will be important in determining the timing of growth and extinction events within discrete populations, and their subsequent response to environmental stressors.