<p>Marine macroalgae and aquaculture organisms have in common to form problematic biomass, either when washed ashore after extensive blooms or as processing remains, which accumulate in aquaculture facilities. Both sources of biomass are commonly regarded as waste. This study aimed to investigate whether both sources of waste can be combined in a beneficial way to yield value-added products. Crude extracts of shrimp (<i>Penaeus vannamei</i>) and crayfish (<i>Cherax quadricarinatus</i>) remains were analyzed for their catalytic potential and functional properties. Shrimp extracts showed a high potential for degrading β-1,3-glycosidic bonds (laminarin), while crayfish extracts showed a high potential for degrading β-1,4-glycosidic bonds (cellulose). The highest activities were observed at pH 4 to pH 6 and at 50 to 60 °C, with an optimum range between 30 and 40 °C. Pre-treated brown algae, <i>Sargassum horridum</i>, were incubated with the crude crustacean extracts. The extracts were capable of hydrolyzing brown algae biomass, thereby liberating glucose. Blends of shrimp and crayfish extracts were more efficient than shrimp extracts alone. The produced glucose was fermented by common yeast to bio-ethanol. This “proof of concept” showed that putative bio-waste can be utilized to extract active enzymes and suitable substrates for the production of value-added products such as bio-ethanol. This approach of combining two different sources of waste in a complementary process may contribute to the mitigation of marine bio-waste and be considered a valuable feedstock for biotechnological applications.</p> Graphical Abstract <p></p>