Seasonal variations of dissolved free, total and particulate enantiomeric amino acids were investigated in eutrophic (middle-inner) to oligotrophic (outer) parts of the Izmir Bay. Mean dissolved free, dissolved combined, total dissolved hydrolysable and particulate hydrolysable amino acid levels in middle-inner parts were higher than that of outer part, and found as 232.5, 757.3, 989.8 and 20.9 nM, respectively. Among all amino acid forms, highest mol percentages were found for glycine and L-glutamate. Total D-enantiomers in all forms were only present at trace amounts (<= 10%). While dissolved organic carbon and nitrogen enriched with freshly produced dissolved amino acids especially in spring, degradation processes were dominant in summer and autumn. According to degradation index of DFAA, seasonal production and degradation were balanced in eutrophic middle-inner bays. On the other hand, seasonally constant fresh production was observed in oligotrophic outer bay. Seasonal and spatial variations of amino acids and organic matter pools in eutrophic and oligotrophic waters of Izmir Bay were under the influences of autochthonous and allochthonous processes. (C) 2021 Elsevier B.V. All rights reserved.