A fully transient, 2-dimensional physical and biological model has been developed to quantify the seasonal cycle of silica in the estuaries-coastal zone continuum of the Bay of Brest (France). The numerical model includes an explicit representation of the benthic-pelagic coupling, which is stimulated by the increasing density of an invasive megabenthic filter feeder, the slipper limpet Crepidula fornicata. The selected spatial resolution allows resolution of the heterogeneous density distribution of these organisms in the bay. Results show that the benthic nutrient dynamics are highly variable and strongly depend on the local conditions. This heterogeneity is not reflected in the pelagic phytoplankton population dynamics because transport and mixing homogenize the distribution of nutrients and biomass. A seasonally resolved silica budget over the entire bay and estuaries emphasizes the important contribution of the benthic recycling fluxes to the supply of dissolved silica (dSi) during the productive period (~50% from 1 April to 1 September). In a prognostic scenario which forecasts the impact of removing the invasive benthic filter feeders, the dSi efflux is reduced by 63% and a pronounced harmful algal bloom of dinoflagellates develops in late summer.

The Pacific oyster, Crassostrea gigas, is an invasive species with a large increase in prevalence globally, and with potential of spreading even more because of climate-change effects. We examined how future climate might affect its potential for spread at its northern distribution limit in a temperate ecoregion, by simulating spawning, larval dispersal, larvae settlement and adult survival, given different climate scenarios. The simulations were performed using a three-dimensional current model (GEMSS) and a specially designed oyster module, applied at the study site in the Oslofjord, Norway. The simulations showed that the expected climate in the middle and latter part of this century, with warmer summers and winters, very likely will lead to increased prevalence of the species within northern Europe. The warmer summers will more often provide favourable temperature conditions for oyster spawning and settlement, and warmer winters will more seldom cause high winter mortality. The simulations gave a realistic picture of the relative frequency and the main distribution pattern observed, given the current climate. The future climate-scenario simulations indicated influence of local differences in temperature on the dispersal pattern. The study indicated increased dispersal and successful establishment at the outer edge of the species present distribution in the future and, hence, an increased risk to native species and habitats in temperate regions.

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The aim of this work is to evaluate core variables of the ecological potential of the Sulejów Reservoir (temperature distribution, flow velocities, and concentrations of selected indicators, e.g., phosphates, nitrates, the abundance of phytoplankton) using a three-dimensional hydrodynamic model, GEMSS-HDM (generalized environmental modeling system for surface waters), coupled with a water quality model, WASP EUTRO (GEMSS-WQM). The monitoring data necessary to build the model were obtained from two multiparameter probes that were submerged in two locations in the Sulejów Reservoir. An ADCP current profiler was used to collect data for hydrodynamic model calibration and verification. Total error between computed and measured velocity was estimated at 10–15%. A high concentration of chlorophyll-a during the vegetation season of 2015 (0.02 mg/L) was coupled with high water temperature (above 25 °C) and low concentrations of biogenic compounds (phosphorus and nitrogen at 0.02 and 0.001 mg/L, respectively). In 2015, NO3-N was the limiting nutrient in the Sulejów Reservoir. Maximum growth of algae was observed in June and July 2015 (0.02 mg/L chla) along the entire length of the reservoir; algae bloom volume reduction was observed in September (0.004 mg/L chla). Proposed scenarios for nutrient reduction—50% reduction of phosphate-phosphorus (PO4-P) and nitrate-nitrogen (NO3-N) from agriculture areas as well as 50% reduction of discharges from septic tanks—led to a considerable reduction of nutrient concentrations in the reservoir waters; it additionally favors reducing the concentration of chlorophyll-a. The obtained results indicate that these sources of pollutants are mainly responsible for the poor water quality status of the reservoir and more intensive eutrophication phenomena.

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