Polluted Mediterranean lagoons deform fish ear bones, signaling ecosystem damage
Researchers found that toxic cocktails of metals and industrial chemicals in Tunisian lagoons physically distort the ear structures of young seabream, a commercially important species. The discovery provides a biological marker that pollution is harming fish health before visible symptoms appear—crucial for regulators monitoring water quality and aquaculture operations protecting food supplies.
Originaltitel: Environmental cocktails of pollutants leave morphological imprints on Seabream otoliths in Mediterranean lagoons.
Föroreningarnas inverkan på fiskuppväxt hotar mediterrane lagunernas värde som växtkammare för kommersiella arter. Forskare undersökte 93 ungdomsfiskar av gilthuvad havsbraxem från tre tunisiska laguner och fann att föroreningar från industriell aktivitet orsakar mätbara missbildningar i otoliter — hörselbenen som styr fiskens balans och orientering. Tunis Lagoon visade högst metallhalter (bly, nickel) och långlivade organiska föroreningar (PCB, DDT, bromerade flamskyddsmedel). Även då muskelkoncentrationer låg under gränsvärdena för livsmedel, påverkade särskilt koppar, rubidium, strontium och DDT otoliternas utveckling. Vänster otoliter visade större asymmetri, tecken på utvecklingsstörning under miljöstress. Resultaten från Frankrike, Tunisien och Sverige erbjuder nya verktyg för att bedöma föroreningsrisker i känsliga lagunhabitats innan effekterna blir synliga i slutna ekosystem eller livsmedelskedjor.
Anthropogenic activities have led to the persistent build-up of trace metals and organic pollutants in coastal ecosystems, threatening aquatic life. Gilthead seabream, a commercially valuable species, often inhabits Mediterranean lagoons that function as vital nursery grounds. In this study, we examined 93 juvenile seabreams from three Tunisian lagoons to evaluate contamination levels and their effects on otolith morphology. We measured inorganic and organic contaminants in fish muscle and investigated their potential effects on otolith shape and asymmetry. Clear fish muscle contamination signatures emerged across sites: Tunis Lagoon exhibited the highest levels of contamination, followed by Ghar El Melh, while El Biban Lagoon appeared relatively pristine. Relatively elevated levels of metals (e.g., Pb, Ni, Be) and persistent organic pollutants (e.g., PCBs, DDTs, PBDEs) were observed in the more impacted lagoons. Notably, we found that otolith shape and fluctuating asymmetry were significantly associated with contaminant exposure, even after accounting for natural variables like fish size and lipid content. Specific pollutants, especially Cu, Rb, Sr and DDT, were linked to altered otolith shape and increased asymmetry, suggesting disrupted biomineralisation. Greater asymmetry observed in the left otolith suggests that sub-lethal stress impairs developmental stability. Although fish muscle contaminant levels generally fell below food safety thresholds, the observed effects on otolith development raise concerns about functional consequences and underlying physiological stress. Our results highlight otolith asymmetry as a sensitive bioindicator of environmental stress in wild fish. By integrating shape analysis with contaminant profiling, this study offers a powerful tool for assessing pollution impacts in vulnerable Mediterranean nursery habitats.