Abstract

The ecological characteristics of the benthic macrofauna make a good indicator to evaluate the effects of anthropic perturbations (e.g., aquaculture, submarine pipelines emissions) on marine ecosystems. Chilean environmental regulation establishes that macrofauna characterization must be performed with sieves with 1,000 mu m opening. To evaluate the loss of information on species composition and abundance by using an opening of 1,000 mu m instead of 500 mu m, subtidal samplings were performed during summer and winter of 2018 in 5 areas of the Gulf of Arauco, central Chile. Sampling and analysis consisted of: (i) samples were sieved through 1,000 mu m mesh and the organisms passing through this sieve were retained in 500 mu m mesh sieves; (ii) identifying the taxa retained in both sieves to the lowest possible level, and (iii) comparison of the macrofauna between sieves, periods and sampling areas, using univariate and multivariate statistics. The analyses showed significant differences in the community structure among sieve sizes, areas and sampling periods. The AMBI and W indexes, used as community bio-indicators, also showed significant differences between sieve sizes. The results revealed that, although a 1,000 mu m sieve can identify spatial and temporal differences in the macrofauna, it underestimates the level of impact shown by community bio-indicators. The use of a 500 mu m sieve is recommended if the objective is to evaluate anthropic impact on the marine environment, especially for baseline studies, preliminary site characterizations for aquaculture, monitoring and/or environmental surveillance programmes. This information should also be complemented with multivariate statistical tools that are capable of incorporating together all the biological and environmental information compiled in the study area.