Storage and export of mercury from a contaminated bay (Ria de Aveiro,Portugal)

Mercury has been determined in water, suspended particulate matter (SPM)and sediments (solid fraction and pore water) collected in a heavilycontaminated confined area (Largo do Laranjo) of the Ria de Aveiro.Mercury has been analysed in seabass (Dicentrarchus labrax) capturedin several locations of the lagoon. The levels of mercury in water and SPMin the contaminated sampled places fluctuated daily with the tide (from 10to 53 ng.dm^-3 and 3.5 to 26 g.g^-1, respectively),indicating the export at the tidal rhythm. Bottom sediments exhibitedhigher concentrations, the maximum (48 g.g^-1) occurringnear the anthropogenic source at depths corresponding to the periods ofhigher industrial discharges. Mercury concentrations in pore waters (max.80 ng.dm^-3) exceed the values found in the water column and werehigher at depths where Acid Volatile Sulphides (AVS) presented broadmaximums. This implies a remobilization at anoxic conditions. However theexport across the sediment-water interface predicted through moleculardiffusion is low (between 1 to 4 × 10^-3 ng.cm^-2.h^-1) incomparison to the industrial input. The anthropogenic mercury appears tobe rapidly accumulated in seabass, a predator fish that enter seasonally inLargo do Laranjo.     

Variability in the settlement of non-indigenous species in benthic communities from an oceanic island

The introduction of non-indigenous species (NIS) in new environments represents a major threat for coastal ecosystems. A good understanding of the mechanisms and magnitude of the impact of NIS colonisation on native ecosystems is becoming increasingly crucial to develop mitigation measures and prevent new invasions. In this present study, we asked if distinct coastal benthic communities from an oceanic island can have different vulnerability to NIS colonisation process. First, PVC settlement plates were deployed for 1 year on the rocky shore of two different locations of Madeira Island (North versus South coast). Then, we implemented a mesocosm experiment where recruited plate communities were maintained under different levels of NIS propagule pressure in order to assess their vulnerability to NIS colonisation process. Results showed that NIS colonisation success was not influenced by the level of propagule pressure, but however, final colonisation patterns varied depending on the origin of the communities. This variability can be attributed to major structural differences between the preponderant species of each community and therefore to the biotic substrate they offer to colonisers. This study highlights how biotic features can alter the NIS colonisation process and importantly, shows that in an urbanisation context, the nature of the resident communities facing invasions risks needs to be closely assessed.     

Role of non-indigenous species in structuring benthic communities after fragmentation events: an experimental approach

Biological Invasions - Habitat loss and fragmentation, and biological invasions are widely considered the most significant threats to global biodiversity. While marine invasions have already shown...