Ocean Deoxygenation Conference | Kiel 2018

In the last 10 years the coast of south-central Chile was strongly perturbed by two events of different origin on a scale of tens to hundreds of kilometers. The first, which occurred in January 2008, was a natural hypoxic event associated with the coastward intrusion of upwelled water low in dissolved oxygen, which produced massive mortality of benthic and planktonic organisms in Coliumo Bay. The second was the world’s sixth strongest earthquake on record (8.8 Mw) and subsequent tsunami that occurred on February 27, 2010, heavily impacting Coliumo and Concepción Bays which are located 25 and 30 km south of the epicenter, respectively. These events provided a unique opportunity to study the dynamics and resilience of benthic communities after major perturbations. Here we analyze the effect that both major perturbations had on the megafaunal community of Coliumo Bay, evaluating its stability and resilience over the following seven years. Either by natural or anthropogenic sources, the benthic environments of both bays are subjected to forcing factors, which modify the oxygenation of the deeper layers of the water column. Quarterly oceanographic surveys were conducted at Coliumo Bay from 2007 to 2017. The megafauna community was sampled using a modified Agassiz trawl. Vertical profiles for salinity, temperature and dissolved oxygen were taken at the sampling sites with a CTD-O.Within approximately three months after the hypoxic event the megafaunal community of Coliumo Bay had returned to conditions similar to those existing prior to the hypoxic event, suggesting a rapid recovery. After the tsunami the megafaunal community (both in density and biomass) shifted inter-annually through different structures, with an apparent directionality. Oceanographic and biological seasonality at Coliumo Bay showed a strong cyclical influence on this inter-annual community response. A spatial homogenization of the community over time (i.e. diversity recovery) took place, probably promoted by ecological functionality of scavenger species and by the proportional increase of non-dominant species. In this community recovery, bottom dissolved oxygen and bathymetry also played a crucial role in the spatial structure. Seven years after the tsunami total density and total community biomass were still considerably below those described for unperturbed conditions (i.e. before 2008), mainly associated with the decrease in density and biomass of dominant species. A comparison of the effects that the tsunami and hypoxic conditions produced on the structure of the benthic communities of Coliumo and Concepción Bay is also reported.
Funding: PIMEX PROGRAM (U.R. 23801.567.552), INCAR (FONDAP-CONICYT 15110027)