MODELING OF EUTROPHICATION INDICATORS CHANGES IN THE GULF OF FINLAND WITH THE EFFECTS OF POLYCHAETES MARENZELLERIA SPP. IN A FUTURE CLIMATE.

The aim of the work is to assess consequences of polychaetes Marenzelleria spp. invasion for the Gulf of Finland ecosystem in a future climate. With this objective benthic submodel of the 3-dimentional eco-hydrodynamic Saint-Petersburg Baltic sea Eutrophication Model (SPBEM) was applied. In the model 4 numerical experiments were carried out: 1) 2 control runs excluding the effects of Marenzelleria spp. under two different scenarios of global climate change (based on ECHAM5 model of Max Planck Institute of Meteorology, Hamburg, Germany and on HadCM3 model of the Hadley Centre in the UK) and 2) 2 runs considering these effects under the same two climate change scenarios. The model was run from 2007 till 2040 years. Results show that in all 4 scenarios cyanobacteria biomass decreases in the future climate that eventually is due to weakening of density stratification in the Gulf of Finland. Allowing for in the model bioirrigation activities of Marenzelleria spp. leads to additional decrease in summer biomass of cyanobacteria. This effect is stronger in HadCM3 scenario (decrease by average 43%) than in ECHAM5 scenario (decrease by 15%). Phosphorus content in the sediments responds to the polychate's activity the opposite way: P increases by 5.6% and 1.75% in ECHAM5 and HadCM3 scenarios, respectively. Hence, model reaction to the allowance for Marenzelleria spp. effects was stronger in a warmer climate (HadCM3 scenario) and this scenario shows strengthening of phosphorus limitation. Thus, bioirrigation activities of invasive Marenzelleria spp. can improve the ecosystem health of the Gulf of Finland in the next three decades through improvement in the oxygen conditions near the bottom. These changes might slow/reduce the intensity of eutrophication. [ABSTRACT FROM AUTHOR]