MEPS 496:85-98 (2014)  -  DOI: https://doi.org/10.3354/meps10592

ABSTRACT: Heart rate (ƒ_H) contributes to control of blood oxygen (O₂) depletion through regulation of the magnitude of pulmonary gas exchange and of peripheral blood flow in diving vertebrates such as penguins. Therefore, we measured ƒ_H during foraging trip dives of emperor penguins Aptenodytes forsteri equipped with digital electrocardiogram (ECG) recorders and time depth recorders (TDRs). Median dive ƒ_H (total heartbeats/duration, 64 beats min^-1) was higher than resting ƒ_H (56 beats min^-1) and was negatively related to dive duration. Median dive ƒ_H in dives greater than the 5.6 min aerobic dive limit (ADL; dive duration associated with the onset of a net accumulation of lactic acid above resting levels) was significantly less than the median dive ƒ_H of dives less than the ADL (58 vs. 66 beats min^-1). ƒ_H profile patterns differed between shallow (<50 m) and deep dives (>250 m), with values usually declining to levels near resting ƒ_H in shallow, short-duration dives, and to levels as low as 10 beats min^-1 during the deepest segments of deep dives. The total number of heartbeats in a dive was variable in shallow dives and consistently high in deep dives. A true bradycardia (ƒ_H below resting levels) during segments of 31% of shallow and deep dives of emperor penguins is consistent with reliance on myoglobin-bound O₂ stores for aerobic muscle metabolism that is especially accentuated during the severe bradycardias of deep dives. Although ƒ_H is low during the deepest segments of deep dives, the total number and distribution of heartbeats in deep, long dives suggest that pulmonary gas exchange and peripheral blood flow primarily occur at shallow depths.

KEY WORDS: Aerobic dive limit · Diving physiology · Electrocardiogram · ECG · Emperor penguin · Gas exchange · Heart rate · Oxygen store management · Peripheral perfusion