Histopathological and physiological response to zinc exposure in Orchestia species from a Tunisian lagoon

The Bizerte lagoon is a highly productive coastal ecosystem, yet it faces constant pressure from human activities and exposure to Zinc. This study compared Zn bioaccumulation in three Orchestia species (Orchestia gammarellus, Orchestia montagui, and Orchestia mediterranea) collected from the lagoon's banks. Individuals were exposed to contaminated soil with three different zinc concentrations, and their biological and physiological responses were assessed. Body zinc concentrations were measured using flame atomic emission spectrometry. Results showed a significant increase in mortality by the second week of exposure, alongside notable differences in body mass variations between species. O. mediterranea exhibited greater resilience to zinc exposure. Zinc accumulation in the Orchestia species was considerably higher than in the surrounding sediment, classifying all three species as macroconcentrators of zinc. Additionally, zinc-contaminated substrates induced structural changes in the amphipods' hepatopancreas, considered as the efficient storage organ, with the most pronounced alterations occurring at the highest zinc concentrations. In O. gammarellus, ultrastructural changes included lipid granules of varying shapes and sizes, while O. montagui and O. mediterranea displayed disrupted cell borders and swollen mitochondria.

This study highlights the sensitivity of Orchestia species to zinc contamination, confirming their potential as bioindicators of metal pollution in coastal environments.