Salmon farming is a relevant activity in southern Chile, so it is necessary that monitoring instruments include indexes that account for the changes that are occurring to preserve biodiversity and the sustainability of this activity. The AZTI Marine Biotic Index (AMBI) classifies macrofauna species into ecological groups (EG) according to their sensitivity to pollution, distinguish various impact levels and establishes an acceptability limit (3.3). The objective of this study was to evaluate the ecological condition of sites exposed and less exposed to salmon farming in subtidal soft bottom systems in the Los Lagos and Aysén regions of southern Chile using the AMBI biotic index.
The sampling design included 4 zones per region (2), 3 sectors per zone, and 3 sites per sector. Sediment samples were obtained using a Van Veen (0.1 m2) grab sampler. The variables analyzed in this study are sediment Redox potential (mV), Total organic matter (TOM) (%), richness, dominance and AMBI. Two-way Analysis of Variance with level of exposure and season of the year as factors were carried out to compare the variables. A regression analysis for ordinal data was used to predict the AMBI based on Potential redox and Dominance indicator.
Exposed zones show lower redox potential, higher i) AMBI values, ii) dominance and iii) % of organic matter than non-exposed zones, which is to be expected due to the entry of organic matter from fish feces and uneaten food. In exposed zones, the most frequent disturbance level is “moderately disturbed” (AMBI>3.3) (Fig. 1 as an example), and unlike the less exposed zones, it is possible to find highly disturbed sites (AMBI>5). Macrobenthic community changes along the redox gradient are different depending on whether it is in an exposed or less exposed area to salmon farming. Future studies should include phosphorus. It could explain differences in community recovery when oxygen availability improves between sites exposed and less exposed to salmon farming.