# Trajectories of trace element accumulation in seagrass (Posidonia oceanica) over a decade reveal the footprint of fish farming

## TL;DR

A study over ten years found that fish farming increases trace element accumulation in seagrass, showing environmental impact.

## Contribution

Long-term tracking of trace elements in seagrass near fish farms reveals historical contamination trends and ecological impacts.

## Key findings

- Rhizome production near fish cages was up to 50% lower than in control areas.
- TE concentrations in dead sheaths showed significant differentiation between Cage and Control stations from 2012–2020.
- Contamination levels increased for certain phytotoxic elements like As, Cu, Cd, Mo, and V near fish farms.

## Abstract

To evaluate the effect of trace element (TE) release from fish farms on seagrass Posidonia oceanica, we compared TE concentrations (As, Cd, Co, Cu, Mn, Mo, Ni, Pb, V, Zn) in shoots near fish cages (Station ‘Cage’) with those away from them (Station ‘Control’) in two fish farm facilities (Site 1 and Site 2, North Aegean Sea, Greece). We assessed the present (i.e., 2021, year of sampling) and past (reconstructed period 2012–2020) accumulation of TEs using the living compartments (leaf blades, sheaths, rhizomes, roots, epiphytes) and the dead sheaths, respectively. We also assessed possible seagrass degradation by reconstructing past rhizome production. P. oceanica rhizome production at the ‘Cage’ stations was up to 50% lower than at the ‘Control’ stations. Most TE concentrations were higher at ‘Cage’ stations, but the differences often depended on the seagrass living compartment. Significant differentiation between ‘Cage’ and ‘Control’ stations was observed based on the TE concentrations of the dead sheaths during 2012–2020. The contamination level at the ‘Cage’ stations was mostly moderate in Site 1 and low in Site 2, during the reconstructed period, while an increasing contamination trend was found for certain potential phytotoxic TEs (As, Cu, Cd, Mo, V). Our results emphasize the need for the aquaculture industry to work towards a more ecologically aware approach.

The online version contains supplementary material available at 10.1007/s11356-024-32910-0.