The present study deals with the distribution of the non-native Polychaete Marenzelleria viridis in the Isefjord Estuary in Denmark and it´s interaction with the macro-benthic fauna community in the fjord. 14 stations were selected in the estuary. M. viridis prevalence was compared to a number of abiotic factors: salinity, sediment composition, organic content and water content in the sediment, in order to investigate M. viridis distribution in relation to habitat characteristics and preferences. The destribution of M. viridis in Isefjorden were also compared with data for M. viridis dispersal in 2008, collected by Olsen et al. (2008). The density of M. viridis from 2008 to 2013 has decreased by 53 % and ranged between 38 and 132 ind./m2, with the highest densities found in the outer part of the estuary. These densities are low compared to other studies. It is assessed that M. viridis follows the classic "boom-bust" pattern, which is typical of invasive species and the invasion of Isefjord currently has moved into an adaptation phase of decline and stabilization of the density of the Polychaet worm as a result. In addition, it is belived that M. viridis in Isefjord primarily is spreading by the means of ballast water from ships in and near ports and shipping channels. It is assessed further that the prevalence of M. viridis in Isefjord is primarily driven by abiotic conditions and not so much by the composition of the native benthic fauna communities. There were found a positive correlation between M. viridis and grain sizes of sediment toward preferences for finer grain sizes relative to the sizes studied in this work. In addition M. viridis ability to maintain a sustainable population in the fjord is questioned, on the basis of high salinitets levels and low nutrient content in relation to M. viridis optimal levels for successful reproduction and larval development. Compared to the interactions with the macro-benthic communities in the system, there were found no significant correlations between M. viridis and the five most important species for the dissimilarity between stations with and stations without M. viridis. This is probably a result of the low density of the Polychaet worm found in Isefjord and it is furthermore belived that M. viridis, at this stage of the invasion has no significant effect on the benthic society as a whole. It is assessed on the basis of studies undertaken during 2008 that M. viridis impacts on society in Isefjord was larger in 2008, however, it must be stressed that there is a clear trend towards the spread of many species decreased at stations where M. viridis were present, compared to stations where M. viridis was not present, although this trend was lower compared to the same trend found in 2008, indicating that M.viridis at higher densities may have an effect on the benthic community here. It is therefore important that the interactions with the native fauna of Isefjorden continue to be monitored and further studies of the physical factors important for the spread of this highly competent invasive species must be investigated.
|Uddannelser||Miljøbiologi, (Bachelor/kandidatuddannelse) Kandidat|
|Udgivelsesdato||28 aug. 2014|
|Vejledere||Gary Thomas Banta|
- Invasive species
- Marenzelleria viridis