To engage undergraduate marine biology students and demonstrate the relevance of energy metabolism to their field, we developed laboratory activities that integrate cellular metabolism with the biology of marine invertebrates. Our approach has the potential to uncover specific adaptations in energy pathways associated with hypoxia tolerance. A key difference between marine invertebrates and vertebrates lies in their anaerobic metabolism. While vertebrates typically utilize lactate dehydrogenase to produce lactate as the end-product of anaerobic glycolysis, marine invertebrates employ a variety of dehydrogenase pathways. This diversity enables efficient anaerobic energy production and reduces the accumulation of harmful byproducts. We used two abundant polychaete species (Nephtys caeca and Alitta virens) found on the eastern Atlantic coast of Canada. Students measured the maximal activities of key enzymes of anaerobic (lactate dehydrogenase, pyruvate kinase, and opine dehydrogenases) and aerobic metabolism (electron transport system, pyruvate kinase, and aspartate aminotransferase). The presence of two opine dehydrogenases (strombine and alanopine) was observed in N. caeca, while lactate dehydrogenase (LDH) activity was marginal. Opine dehydrogenases are homologous to lactate dehydrogenase and help buffer acidification during hypoxia. In A. virens, only LDH is present. As a general marker of aerobic capacity and hypoxia tolerance in invertebrates, malate dehydrogenase activity was high in both species. This laboratory activity introduces undergraduate students to metabolic adaptations and alternative energy pathways in marine life, particularly in the intertidal zone. This activity, conducted at the beginning of the semester, captured their interest and motivated them to study the key theoretical concepts governing animal energetic metabolism.
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