Modelling the seasonal dynamics of marine plankton in the Southern Baltic Sea. Part 1. A Coupled Ecosystem Model

The paper presents a one-dimensional Coupled Ecosystem Model (1DCEM) consisting of three submodels: a meteorological submodel for the physics of the upper layer and a biological submodel, which is also driven by output from the physical submodel. The biological submodel with a high-resolution zooplankton module and a simple prey-predator module consists of seven mass conservation equations. There are six partial second-order differential equations of the diffusion type for phytoplankton, microzooplankton, mesozooplankton, fish, and two nutrient components (total inorganic nitrogen and phosphate). The seventh equation, an ordinary differential equation, describes the development of detritus at the bottom. In this model the mesozooplankton (herbivorous copepods) is represented by only one species – Pseudocalanus elongatus – and is composed of 6 cohorts. The fish predator is represented by 3 cohorts of early juvenile herring Clupea harengus. Hence, the biological submodel consists of an additional twelve equations, six for weights and six for the numbers in 6 cohorts of P. elongatus, and three equations for the biomasses of 3 predator cohorts. This model is an effective tool for solving the problem of ecosystem bioproductivity and was tested in Part 2 for one partcular year.