Effects of shoreline discharge of iron mine tailings on a marine soft-bottom community in northern Chile.

This study evaluates the magnitude and extension of the impact produced by the discharge of inert allochthonous materials, including clays and particulate iron, on macrobenthic soft-bottom assemblages in the subtidal zone of a coastal bay in north-central Chile. An average of 118 Ton h(-1) of finely divided solids were discharged into the rocky intertidal zone of the bay for a period of over 16 years, producing continuous turbidity in the water column and sedimentation in the subtidal zone. Data obtained four months before cessation of the discharge showed that the macrofauna present at 20 and 50 m depth in the bay suffered an important decrease in abundance and species richness, low diversity/high dominance, and deep changes in community structure related to the discharge. The faunal assemblages present at 110 m depth did not show effects from the discharge, suggesting that the impact was limited to the inner part of the bay. The impoverished faunal aggregates at 20 and 50 m depth showed exclusive domination by the Lumbrineris bifilaris (polychaete)-Diastylis tongoyensis (cumacean) association, representing a simple trophic guild of deposit feeders. The complete absence of opportunistic species such as capitellid, spionid, and/or cirratulid polychaetes may be associated with the turbidity and sedimentation levels in the bay.