Petras Zemlys

Connectivity in Three European Coastal Lagoons

The temporal variation and the spatial structure of marine populations strongly depend on the early life stages of the individuals and on their interaction with the environment. The physical dispersion of propagules (eggs and larvae) is a fundamental aspect, conditioning the successful recruitment of juveniles in the adult population. Coastal transitional ecosystems such as lagoons plays a role of nursery for species with economic relevance, such as demersal fishes, mollusks and crustaceans. Those environments promote the recruitment of the early stages for several organisms because they act as area of retention for propagules and concentration for resources. We applied in three different European coastal lagoon a lagrangian particle tracking model coupled with a hydrodynamic model, and developed a method to evaluate the connectivity inside a lagoon and between a lagoon and the sea. Each particle represents a generic passive pelagic larva with a duration of one month. The average connectivity has been estimated after two years of simulation under realistic tide and wind forcings. Our results allow to characterize the lagoons behavior considering different spatial scales and to compare the dynamics of different systems. This study is a first step toward a better knowledge of the factors influencing the ecological role of coastal lagoons.

2D finite element ecological model for the Curonian lagoon

The results of application of 2D finite element model SHYFEM to the Curonian lagoon (Baltic Sea) are considered. SHYFEM consist of a physical processes module and an eutrophication module EUTRO adapted for the SHYFEM code from well known modelling system WASP. The SHYFEM/EUTRO model calibration results were compared with the performance of various biogeochemical models analysed in other studies (153 studies published from 1990 to 2002). The performance of all corresponding state variables—dissolved oxygen, NO3, NH4, PO4, phyto- and zooplankton—was slightly lower than median model performance which could be considered satisfactory given the initial state of model formulation and calibration. Model underestimates phytoplankton autumn blooms, especially for the southern part of the lagoon, where fine sediments dominate and water residence time is high. It can be concluded that, in order to increase model performance, the eutrophication module should be improved to account for the dominance of different phytoplankton groups as well as for the exchanges between the sediments and the water column. The amount and quality of the data available for the model setup and calibration are unsatisfactory and should be improved for the development of the next enhanced model version.

Revision pre-ingestive selection efficiency definition for suspension feeding bivalves: facilitating the material fluxes modelling

The importance of the particle selective feeding of bivalves becomes more evident and it is necessary to incorporate this phenomenon into ecological models in order to reflect correctly the material fluxes inside the organism and ecosystem as well. The problems related to the modelling of organic matter selection are considered in this paper and a new definition of pre-ingestive selection efficiency is proposed. It differs from the classical one in using the organic material fraction in ingested food instead of pseudofaeces. The newly defined selection efficiency exhibits an advantage in simplified shape of experimental relationship to the organic matter fraction in seston and easier derivation of formulas related to mathematical food processing formulation.

Linking NPZD and foodweb models of an estuarine lagoon ecosystem

Among aquatic ecosystems, estuarine lagoons are generally more complex than inland waters because of the combined effect of the land and the sea. These systems are under the influence of land through the rivers and have a restricted and temporally variable water exchange with the seas or the oceans. Estuarine lagoons are generally productive ecosystems which offer habitats for many species. Many coastal and estuarine lagoons are known to be important components of the natural capital providing opportunities for aquaculture. These ecosystems are difficult to analyze. Like most of the transitional waters, their trophic and ecological status cannot be defined easily because of their complexity. Most of them are usually under strong human influence or already modified heavily, which makes this task even more difficult. Nutrient phytoplankton zooplankton detritus (NPZD) models can help scientists to analyze the full picture of an aquatic system, together with physical, chemical and biological processes, to fill in the gaps of data between samplings and to forecast environmental changes and use this output for planning. Traditionally, these models have been developed and used by engineers extensively, usually with the aim of water resources and quality management. However, different needs may arise in ecological studies with different aims such as better understanding how an aquatic ecosystem works or analyze the interactions in an aquatic food web. In this case, different state variables may be needed than the conventional ones, which are used by more general water quality models that are available. In ecological studies, related to coastal lagoon ecosystems organism groups on the higher trophic levels can be of interest. In this study, an NPZD model and a trophic network model that contains organism groups on the higher trophic levels were linked using the ldquobottom-up controlrdquo approach. Such a linkage of models provides the possibility to use the advantages of both models; reproducing of the erratic behavior of nutrients and plankton as realistic as possible, while still taking the more complex organisms in the trophic network, which respond to external forcing in a larger time scale. The models developed in this study were applied to the Curonian Lagoon that is an important estuarine ecosystem for Lithuania.

Assessment of the effects of variation in external nutrient loads on the Curonian lagoon ecosystem

Curonian lagoon, the largest coastal lagoon in Europe is characterized by the strong seasonal and interannual variation in nutrient loads and water quality parameters is characterized by the dominance of the Nemunas rivers discharges. Coupled hydrodynamic and NPZD model was applied to assess the impacts of the foreseen reduction of nutrient loads prescribed in the State Plan to Improve the Quality in the Curonian lagoon, which was approved in 2006. The simulation of 1999-2000 was used as the background scenario. The NPZD model applied takes into the account the recently evaluated atmospheric nitrogen fixation by the cyanobacteria during the summer ldquobloomsrdquo and combined effects of temperature and wind climate.

Modelling Particle Selection Efficiency of Bivalve Suspension Feeders

The choice of an appropriate index to adequately describe the efficiency of pre-ingestive organic material selection is important for modelling the material flux within the suspension feeding process. Recently, a new selection efficiency index was suggested by Zemlys et al. (2003) which simplifies the quantification of the selection activity. A simple equation with interpretable parameters calculates the selection efficiency index using literature values of uptake rate and food quality. This analysis suggests the possibility of developing more general and biologically interpretable models.