Novel polymeric packaging materials susceptible to environmentally friendly decomposition appeared on the global market. The paper is devoted to an investigation of the impact of degradable polymer packaging on marine life. The chosen polymer was a commercial packaging based on thermoplastic starch (TPS over 85%). The microorganism chosen was Phaeodactylum tricornutum diatom (identified in many aquatic reservoirs, with a tendency to flow with seawater plankton in places of great saline oscillation). The packaging material was incubated both in natural seawater and in the presence of diatom population. The chlorophyll a content was determined as the criterion of diatom growth in the presence of tested polymers. The polymer surface and the colour changes in the diatom culture were recorded photographically. The presence of polymeric samples significantly changed the kinetic of diatom growth in seawater during incubation affecting its biological balance. During the experiment in seawater, diatom adhered to polymer surfaces and the polymer stimulated their growth.