Temperature-induced changes in the locomotor capacity of juveniles of Marenzelleria viridis (Polychaeta, Spionidae)

Abstract. Populations of Marenzelleria viridis in the Chester River (Kent County, Maryland) experience temperatures ranging from over 30°C in summer to near freezing in winter. Interestingly, M. viridis swims actively in winter. This observation led us to examine the relationship between locomotor capacity and temperature in individuals of M. viridis . Juvenile specimens were collected in February ("cold animals") and June ("warm animals"). Video analysis revealed that swimming is achieved by flexing the body in cyclic, helical waves. Wave frequencies were measured as an index of locomotor capacity at 5°C, 15°C, and 25°C. The mean wave frequencies of cold animals were 5.4 Hz at 5°C and 7.1 Hz at 15°C (Q₁₀= 1.3); the mean wave frequencies of warm animals were 6.1 Hz at 15°C and 7.8 Hz at 25°C (Q₁₀= 1.3). The effects of changes in water viscosity on wave frequency between 5–25°C were not significant. These results demonstrate that the temperature sensitivity of locomotor capacity in juvenile M. viridis is quite low. We conclude that low temperature sensitivity enables M. viridis to be active throughout the year.