Respiratory and Circulatory Changes in the Lobster (Homarus Vulgaris) During Long Term Exposure to Moderate Hypoxia

Abstract

Within a few hours of the lobsters being placed in the experimental chamber in normoxic water (P_o2, 130-135 mmHg), their heart rate, oxygen uptake (V_o2) and ventilation volume (V_u) were relatively high. The scaphognathites were simultaneously active on both sides (bilateral ventilation) for 50% of the time, active on one side only (unilateral ventilation) for 32% of the time and simultaneously inactive (respiratory pause) for 18% of the time. Percentage extraction of O₂ (% Ext.) was relatively low. 48h after having been set up, heart rate, V_O2 and V_g had decreased significantly, % Ext. had increased and bilateral ventilation occupied 25% of the time. Heart rate was low and the beat irregular. Upon subsequent exposure to hypoxia (P_O2, 50-55 mmHg), P_a, O₂, fell, there was initial hyperventilation, bilateral ventilation for 89% of the time, heart beat was more regular but V_o2 did not change significantly. An initial increase in pHa caused the O₂ affinity of the Hey to rise. After 72h exposure to hypoxia V_g and pHa had declined, but V_g was still higher than at the end of the period of normoxia. Blood lactate, V_o2 and % Ext. were not significantly different from the values recorded after 48 h in normoxic water. Upon return to normoxic water, V_g and the time the animals spent ventilating both branchial chambers fell, but V_o2 increased. It is concluded that for settled lobsters, V_o2 could be maintained during moderate hypoxia by increasing V_g maintaining a regular heart beat, and at least initially by increasing the O₂ affinity of the Hey.