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Individual study: Biological recovery from organic enrichment: some systems cope better than others

Published source details

Macleod C., Moltschaniwskyj N., Crawford C. & Forbes S. (2007) Biological recovery from organic enrichment: some systems cope better than others. Marine Ecology Progress Series, 342, 41-53

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Leave a fallow period during fish/shellfish farming Subtidal Benthic Invertebrate Conservation

A replicated, before-and-after, site comparison study in 2001–2003 at two soft seabed locations in the Tasman Sea, southeastern Tasmania, Australia (Macleod et al. 2007 – same experimental set-up as Macleod et al. 2006) found that after a three-month fallow period invertebrate community composition had changed at farmed sites. After the fallow period (no fish in cages), communities were different to that of the pre-fallow period (fish in cages), and similar to communities present before fish were added (empty cages), but not to that of nearby sites without fish farms (natural seabed). Community data were reported as statistical model results and graphical analyses). Although not tested for statistical significance, at one location, abundances of three pollution-indicator polychaete worms tended to be lower after the fallow period (Capitella capitata pre-fallow: 17,248 post-fallow: 2,621; Neanthes cricognatha pre-fallow: 199 post-fallow: 94; Maldanidae sp. pre-fallow: 54 post-fallow: 0 individuals/m2), but remained higher than at sites without fish farms (Capitella capitata 5; Neanthes cricognatha 4; Maldanidae sp. 0 individual/m2). At the second location, abundances of the opportunistic worms Capitella capitata and Nebalia longicornis tended to be lower following the fallow period (Capitella capitata pre-fallow: 7,470 post-fallow: 5,525; Nebalia longicornis: pre-fallow: 14,902 post-fallow: 1,791 individuals/m2) but remained higher than at sites without fish farms (Capitella capitata: 19; Nebalia longicornis: 0). Sediment samples were collected using a grab (0.07 m2) at 20 m depth. At each of the two locations, five samples were collected at farmed and unfarmed (located 150 m away) sites before fish were added, following nine months of fish farming (pre-fallow period), and following the three-month fallow period. Invertebrates (>1 mm) were identified and counted.

(Summarised by Anaëlle Lemasson)