Adaptations to intertidal life: divergence of energy metabolism enzyme pathways in marine polychaetes

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. Whereas vertebrates typically utilize lactate dehydrogenase (LDH) 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 by-products. 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 (LDH, pyruvate kinase, and opine dehydrogenases) and aerobic (electron transport system, pyruvate kinase, malate dehydrogenase, and aspartate aminotransferase) metabolism. The presence of two opine dehydrogenases (strombine and alanopine) was observed in N. caeca, whereas LDH activity was marginal. Opine dehydrogenases are homologous to LDH 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.NEW & NOTEWORTHY Polychaetes (bristle worms) are common in the marine coastal area of the North Atlantic. Some are active, and others are more sedentary, but most of them are regularly exposed to hypoxic conditions. To reveal potential adaptations that meet their bioenergetic requirements, students explored their cellular enzymatic machinery and compared two species in terms of their strategies for exploiting the habitat.