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Petihakis, G., Smith, C. J., Triantafyllou, G., Sourlantzis, G., Papadopoulou, K-N., Pollani, A., and Korres, G. 2007. Scenario testing of fisheries management strategies using a high resolution ERSEM–POM ecosystem model. – ICES Journal of Marine Science, 64: 1627–1640. [ABSTRACT FROM PUBLISHER]

Abstract: The semi-enclosed environment of Pagasitikos Gulf was the object of a holistic study during 1998–1999 following the appearance of mucilaginous events during summer. A major part of the INSEA project was the development and implementation of a coupled modeling system capable of reproducing all the major characteristics both in physical and biological environments. In the present work the hydrodynamic model based on the Princeton Ocean Model (POM) code is presented while the functioning of Pagasitikos Gulf is analyzed through the assessment of model results. Model results indicate intense seasonal variability with moderate flow patterns and substantial horizontal and vertical gradients. The main known climatological circulation features are found to be reproduced quite well by the model with a rich eddy field controlled by surface buoyancy and momentum fluxes. The ultimate goal is the development of a future operational forecasting system encompassing a detailed description of the ecosystem processes and advanced data assimilation techniques. [Copyright &y& Elsevier]

Abstract: Pagasitikos gulf is a semi-enclosed basin highly influenced both by anthropogenic activities (inflow of nutrients at the north and west parts) as well as by water exchange between the gulf and the Aegean Sea at its south part (Trikeri channel) resulting in the development of functional sub-areas within the gulf. Thus the inner part is characterised by eutrophic conditions with sporadic formation of harmful algal blooms whilst the central part acts as a buffer with mesotrophic characteristics influenced by the outer area. In a companion paper, the circulation fields and the development of water masses in the Pagasitikos gulf were explored. The aim of this study is to investigate the interactions between the physical and biogeochemical systems in the Pagasitikos gulf by coupling advanced hydrodynamic and ecological models. The simulation system comprises two on-line coupled sub-models: a three-dimensional hydrodynamic model based on the Princeton Ocean Model (POM) and an ecological model adapted from the European Regional Seas Ecosystem Model (ERSEM) for this specific ecosystem. After a model spin up period of 10years, the results from an annual simulation are presented. Emphasis is given to the description of the spatial and temporal variability of the ecosystem parameters as well as to the relationship between physical forcing and the evolution of the ecosystem along with other factors affecting the nutrient cycling and primary production. A cost function is used for the validation of model results with field data. Simulation results are in good agreement with in-situ data illustrating the role of the physical processes in determining the evolution and variability of the ecosystem, as well as highlighting the potential usefulness of the model as an operational tool to support environmental management decisions. [Copyright &y& Elsevier]

Abstract: In order to support management decisions for aquaculture, a modeling tool capable of simulating the ecosystem response was developed and is presented here. The impact on the Pagasitikos gulf ecosystem from two marine fish farms, one in a well protected cove and one in a more exposed area of the gulf, is explored and analyzed in the framework of the INSEA EU project. Model results show little effects of nutrient inputs near the exposed site. It appears that effluents from the exposed site may affect more distant areas due to hydrodynamic transport, while effects in the well protected site are more localized and intense (hot spot). Additionally, as the system dynamics are driven to large extent by the seasonal physical variability, the effect depends not only on the location of the farm but also on the season. Planning decisions for coastal areas require integrated management policies based on holistic approaches that include as many system components as possible. The tool capabilities illustrated by the simulation results demonstrate its role in supporting management decisions. [Copyright &y& Elsevier]

Abstract: Within the framework of the European INSEA project, an advanced assimilation system has been implemented for the Pagasitikos Gulf ecosystem. The system is based on a multivariate sequential data assimilation scheme that combines satellite ocean sea color (chlorophyll-a) data with the predictions of a three-dimensional coupled physical–biochemical model of the Pagasitikos Gulf ecosystem presented in a companion paper. The hydrodynamics are solved with a very high resolution (1/100°) implementation of the Princeton Ocean Model (POM). This model is nested within a coarser resolution model of the Aegean Sea which is part of the Greek POSEIDON forecasting system. The forecast of the Aegean Sea model, itself nested and initialized from a Mediterranean implementation of POM, is also used to periodically re-initalize the Pagatisikos hydrodynamics model using variational initialization techniques. The ecosystem dynamics of Pagasitikos are tackled with a stand-alone implementation of the European Seas Ecosystem Model (ERSEM). The assimilation scheme is based on the Singular Evolutive Extended Kalman (SEEK) filter, in which the error statistics are parameterized by means of a suitable set of Empirical Orthogonal Functions (EOFs). The assimilation experiments were performed for year 2003 and additionally for a 9-month period over 2006 during which the physical model was forced with the POSEIDON-ETA 6-hour atmospheric fields. The assimilation system is validated by assessing the relevance of the system in fitting the data, the impact of the assimilation on non-observed biochemical processes and the overall quality of the forecasts. Assimilation of either GlobColour in 2003 or SeaWiFS in 2006 chlorophyll-a data enhances the identification of the ecological state of the Pagasitikos Gulf. Results, however, suggest that subsurface ecological observations are needed to improve the controllability of the ecosystem in the deep layers. [Copyright &y& Elsevier]

Abstract: Pagasitikos Gulf (Greece), presents an interesting area as it depicts strongly non-linear ecosystem characteristics. It is a shallow coastal area where the marine ecosystem picture is strongly influenced by non-linear hydrodynamic interactions and instabilities. In this study, we explore and assess the major influential variables of the surface phytoplankton biomass (Chlorophyll-a). Several different physical and biogeochemical parameters were used (sea surface temperature [SST], mixed layer depth [MLD], salinity, phosphates and nitrates) to identify which variables control or significantly affect the surface Chl-a of Pagasitikos Gulf for the period of 2001–2005. The variables were derived from a coupled hydrodynamic-biogeochemical model and remotely sensed data from SeaWiFS and AVHRR sensor. Generalised Additive Models (GAMs) were used to examine the relationships between Chlorophyll-a and the environmental regime. GAM analysis showed that the combined effects of the variables used, explained 71% of the surface chlorophyll variation. The order of importance of the variables (based on GAM probability) is p =0.01 (for both phosphate and nitrate), MLD: p =0.0197, salinity: p =0.022, and SST: p =0.046. The results clearly indicated the importance of deep mixing for Pagasitikos Gulf, as the surface phytoplankton blooms appeared to be favoured by cold, nutrient rich, well mixed and higher salinity waters. GAMs indicated that SST plays a significant role having a strong negative relationship with Chl-a, where the highest concentration is reached at 12–15°C and minimum at 22–26°C. Chl-a ceases to increase after 37.9‰ of salinity and 40m of MLD, while minimum concentration is found at 10m of MLD, with a subsequent increase as the waters become more mixed. Phosphate and nitrates appeared to be of equal importance with Chl-a exhibiting an increase along with the nutrients. [Copyright &y& Elsevier]

The Pagasitikos gulf ecosystem is studied through the analysis of experimental field data acquired during several monitoring projects and the application of a complex biogeochemical model. The gulf was separated into three different parts (internal, top central-external, bottom central-external) according to the patterns exhibited by the key ecosystem indicators. Unlike other semi-enclosed gulfs Pagasitikos can be characterised as meso-oligotrophic undergoing periods of P or N limitation. Although the signal of nutrient inputs is not very clear in the field data, their importance is assessed through simulation. Increased phosphate concentrations either due to mixing or due to anthropogenic activities can result in phytoplanktonic blooms with significant contribution by diatoms. The effect of hydrodynamic patterns on primary production has been demonstrated through ecosystem modeling indicating that due to long stratification periods, all nutrients released through the benthic regeneration are trapped in the deeper layers, developing a microbial food web. However when the thermocline erodes nutrients find their way up in the upper layers of the euphotic zone and the system turns into more classical type with primary producers growing significantly faster.