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Aquaculture Environment Interactions

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AEI 2:105-115 (2012)  -  DOI:

Indirect effects of fish cage aquaculture on shallow Posidonia oceanica seagrass patches in coastal Greek waters

Konstantine J. Rountos1,*, Bradley J. Peterson1, Ioannis Karakassis2

1School for Marine and Atmospheric Sciences (SoMAS), Stony Brook University, Stony Brook, New York 11794-5000, USA
2Marine Ecology Laboratory, Biology Department, University of Crete, PO Box 2208, 71409 Heraklion, Crete, Greece

ABSTRACT: Over the last 3 decades fish cage aquaculture has increased exponentially in the eastern Mediterranean Sea and has induced various levels of environmental change in coastal waters. The most apparent negative changes involve the degradation of the native seagrass Posidonia oceanica (L.) Delile. Our study examined the effects of fish cage aquaculture on seagrass health, sea urchin density and herbivore feeding pressure in shallow seagrass patches in the coastal waters of 2 Greek islands (Evia and Crete) between February and May of 2008. Evia and Crete represent a wide range of fish farming intensities, from small-scale (75 t yr−1) to large-scale (1000 t yr−1) fish production, respectively. On both islands, the seagrass variables, shoot productivity, standing crop and leaf morphometrics (length and width) were significantly lower (p < 0.0001) in impacted seagrass patches adjacent to fish farms compared with control patches. In addition, significantly higher sea urchin densities and herbivore feeding pressure (percentage of shoots with herbivore grazing scars) were found in impacted patches on both islands. Higher leaf tissue nitrogen and epiphyte loads were also found in impacted patches, but these increases could not be attributed to fish farming alone. Our results show that negative effects on seagrass patches can occur as a result of fish farming at both small-scale and large-scale intensities and that increased sea urchin densities and feeding pressures are important indirect effects of coastal aquaculture on these islands.

KEY WORDS: Aquaculture · Seagrass · Posidonia oceanica · Paracentrotus lividus · Nitrogen · ­Herbivory · Indirect effects

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Cite this article as: Rountos KJ, Peterson BJ, Karakassis I (2012) Indirect effects of fish cage aquaculture on shallow Posidonia oceanica seagrass patches in coastal Greek waters. Aquacult Environ Interact 2:105-115.

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