Franco, M.; Steyaert, M.; Cabral, H.; Tenreiro, R.; Chambel, L.; Vincx, M.; Costa, M.; Vanaverbeke, J. (2008). Impact of discards of beam trawl fishing on the nematode community from the Tagus estuary (Portugal). Marine Pollution Bulletin. 56(10): 1728-1736.
The impact of dead discards, originating from beam trawl fishing on the nematode community from the
Tagus estuary was investigated in terms of vertical distribution of the dominant nematode groups. Sediment
cores were collected from a mud-flat from the Tagus estuary. Crangon crangon (Linnaeus, 1758)
carcasses were added to the surface of the cores, simulating the settling of dead discards on the sediment.
The vertical distribution of the dominant nematode groups was determined up to 4 cm deep at four different
moments in time post deposition (0, 2, 4 and 6 h) and compared to control cores. The C. crangon
addition to the sediment led to the formation of black spots and therefore oxygen depleted areas at
the sediment surface. The Chromadora/Ptycholaimellus group, normally dominant at the surface layer,
migrated downwards due to their high sensibility to toxic conditions. Sabatieria presented the opposite
trend and became the dominant group at the surface layer. Since Sabatieria is tolerant to oxygen stressed
conditions and high sulphide concentrations, we suggest that it migrated opportunistically towards an
unoccupied niche. Daptonema, Metachromadora and Terschellingia did not show any vertical migration,
reflecting their tolerance to anoxic and high sulphidic conditions. Our study showed that an accumulation
of dead discards at the sediment surface might therefore alter the nematode community vertical distribution.
This effect is apparently closely related to toxic conditions in the sediment, induced by the
deposition of C. crangon at the sediment surface. These alterations might be temporal and reflect an adaptation
of the nematode community to dynamic intertidal environments.
