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Research conducted by the University of Oxford claims that the rapid expansion of fish farms in the Mediterranean Sea is killing wide swaths of Posidonia oceanica, a seagrass that’s endemic to the Mediterranean and vital to biodiversity and carbon sequestration in the region.

‬Widespread loss of the Mediterranean’s dominant seagrass species,‬‭ Posidonia oceanica‬‭, have‬‭ been documented over the past two decades and are expected to increase under imminent‬‭ aquaculture expansion plans. This study aims to investigate historic and current impacts of fish‬‭ farming on‬‭ P. oceanica‬‭ meadows around the island of‬‭ Poros, Greece, aiming to quantify the‬‭ magnitude, spatial extent, and persistence of potential health declines, to establish baseline‬‭ conditions for future monitoring and to anticipate future impacts. By Emily Jones. Supervised by Dr. Gwilym Rowlands, Dr. Nancy Burrell & Dr. Katrina Davis.

A University of Oxford study has documented ecological degradation of Posidonia oceanica meadows in Poros, Greece, linked to long-term fish farming impacts extending up to 14 years after farm removal and as far as 900 metres from former sites.

Overabundance of fish farms is a risk to both the marine environment and the economy. By Christos Logaras

Independent journalist Francesco De Augustinis explores the impact of the Area of Industrial Development of Aquaculture planned for Aetolia-Akarnania in Western Greece, where fish cages will occupy 100 hectares and another 100 hectares will be used for other activities. Inhabitants of the islands and villages protest against the fish farms and any further expansion project. In the past ten years they have watched their sea become contaminated and poor in natural resources. The industrial fisheries at Western Greece have also had an impact on Posidonia meadows, which is now absent or very deteriorated.

Marine cage aquaculture has the potential to severely impact Posidonia oceanica seagrass meadows and its associated fauna. In order to assess the impact of fish farming in a littoral bay of Corsica, France, physico-chemical (mud and organic matter) and biological (density and compactness of P. oceanica beds and associated macrofauna) variables have been examined in two stations putatively impacted to different degrees (St1 and St2) and in two unimpacted stations (Controls: C1 and C2). Principal Component Analysis of meadow structural variables (shoot density and compactness of matte) and abiotic variables (mud and organic matter percentage into sediment) highlighted differences among stations and, particularly, differences between impacted stations and controls. Results from C1 and C2 totally overlapped. St1 was the station which differed the most from controls. Compared with control stations, St1 and St2 were characterized by higher values of organic matter and mud and by lower values of shoot density and matte compactness. Permutational multivariate analysis of variance (PERMANOVA) did not show significant differences between C1 and C2 in the structure of macrofauna assemblages, whereas significant differences between the two impacted sites and between these and the control conditions emerged. Differences in assemblages were well correlated with the measured abiotic variables. The analysis showed that the species most responsible for difference among stations were typical of muddy sediment with high organic matter content. These species had higher mean abundance values at impacted stations than at controls. This study suggests fish farming determines an increase of organic matter and sedimentation, which resolve in changes in structural properties of the seagrass meadows and, consequently, changes in the associated macrofauna assemblages.