Intra-annual distribution of Temora longicornis biomass in the Gulf of Gdańsk (the southern Baltic Sea) – numerical simulations

A population model of the copepod Temora longicornis coupled with the ecosystem model 3D CEMBS (Coupled Ecosystem Model of the Baltic Sea) was used to determine the intra-annual distribution of the species biomass in the Gdańsk Basin (the southern Baltic Sea). The population model for T. longicornis consists of twelve equations for twelve state variables, six for mass and six for abundance, i.e. two state variables for each of the six model stages of the development: eggs (Egg), non-feeding stage (N1), subsequent nauplii stages (N2–N6), two copepodite stages (C1–C3 and C4–C5) and adults (C6). The empirical validation of the population model was based on in situ data collected in 2010 and 2011 in the Gdańsk Deep and the western part of the Gulf of Gdańsk. The highest values of the model biomass occurred in the period of high water temperatures – in June 2010 and July 2011 in the Gulf of Gdańsk (ca 5200 mg wet weight (w.w.) m–2 and 6300 mg w.w. m–2), and for almost the whole summer in the Gdańsk Deep (24 500 mg w.w. m–2 and 27 800 mg w.w. m–2). Temora longicornis produced 4 to 5 generations per year in the Gulf of Gdańsk and Gdańsk Deep, respectively. The population model was satisfactorily verified and the calculated results were consistent with the in situ data. Despite some differences between the field and model data, the developed population model of T. longicornis is the first model for this species in the Baltic Sea and, even though it needs further improvement, it can be a useful tool for determining the population dynamics of the species and ecological relationships in the environment.