An introductory subject on the principles of marine chemistry and marine chemical ecology. Definition and history of marine chemistry and chemical ecology. Properties and chemical composition of seawater. Major elements in seawater. Conservative and non-conservative elements. Biogeochemical cycles. Horizontal and vertical distribution of biolimiting elements. Determination of nutrients in seawater. Minor or trace elements in seawater, sediments and marine organisms. Bioaccumulation and biomagnification of trace elements in marine organisms. Trace element speciation and toxicity. Carbonate equilibria in the sea. Ecological role of dissolved organic carbon (DOC) compounds in seawater. Chemical communication conveyed by DOC, allochemical effects. Invertebrate-toxic host relationships, symbiosis and mutualism, coral spawning chemistry. Fatty acids, steroids, terpenes, nitrogenous compounds, fish and shellfish toxins. Potential applications of marine biotechnology-ectocrines and filter feeders, mollusk chemistry, tunichromes, metal ion sequestering and pharmacological activity.