VERMEER: EFFECTS OF EXPOSURE ON SPINY LOBSTER 



Desiccation Rate 



Desiccation rate results are only valid for the 

 range of weather conditions previously specified. 

 Higher temperature and wind speed increases desic- 

 cation rate whereas higher relative humidity de- 

 creases it. 



Because rate of water loss is directly proportional 

 to surface area, smaller spiny lobsters, with higher 

 surface area to volume ratios, lose water at a faster 

 rate. If desiccation is indeed a major stress factor, 

 smaller (sublegal) spiny lobsters will be more 

 affected. 



This size-desiccation rate relationship has also 

 been noted by other investigators. Lazo-Wasem 

 (1984) reported that smaller terrestrial amphipods, 

 Arcitalitrus sylvaticus, lost water faster than did 

 larger amphipods; he suggested a higher surface 

 area to volume ratio and higher respiratory rate of 

 smaller amphipods as two possible explanations. 

 Davies (1969) reported that rate of water loss in a 

 limpet. Patella sp., varied inversely with body 

 weight. Price (1980) reported similar results in an 

 intertidal snail, Melampus bidentatus. 



Spiny lobsters exposed for 2 h lost only 3.6-4.7% 

 of their initial weight, so it is unlikely that simple 

 dehydration is a major source of exposure stress. 

 This conclusion is supported by experiments show- 

 ing that periodic wetting of spiny lobster with sea- 

 water during exposure did not improve survival 

 (Hunt et al. 1986). McLeese (1965) also reported that 

 continuous sprays of seawater did not increase sur- 

 vival of air-exposed northern lobsters, Homarus 

 americanus. It has been suggested that gill damage 

 caused by dehydration may contribute to docu- 

 mented mortality in exposed western rock lobsters, 

 Panulirus cygnus (Anonymous 1980), but this has 

 not been demonstrated. 



Hemolymph Chemistry 



Subtidal crustaceans are unable to extract oxy- 

 gen effectively from air. In Cancer productus, gas 

 exchange rate is reduced fivefold in air (deFur and 

 McMahon 1978). The European lobster, Homarus 

 vulgaris, only extracts one-seventh as much oxygen 

 from air as from water (Thomas 1954). It has not 

 been reported how much aerial respiration P. argv^ 

 can achieve, but the rapid transition to anaerobic 

 metabolism during exposure indicates oxygen ex- 

 traction from air is not adequate to support normal 

 aerobic metabolism. Although gill bailers continue 

 their paddle-like motions in air, loss of fluid support 

 for gill filaments causes them to collapse (pers. obs.). 



Loss of gill surface area for gaseous exchange, 

 coupled with a probable reduction in gill bailer effi- 

 ciency in air, leads to the hemolymph chemistry 

 changes observed. Lactic acid, the primary product 

 of crustacean anaerobic glycolysis (Albert and 

 Ellington 1985) accumulates in quantities sufficient 

 to overwhelm protein and bicarbonate-carbonic acid 

 hemolymph buffering. Taylor and Wheatly (1980) 

 reported a 0.44 unit drop in arterial pH for the 

 crayfish, AustropotaTnohius pallipes, after 3 h of air 

 exposure. They attributed this acidosis to a tenfold 

 increase in hemolymph lactate and to accumulation 

 of COg. Organisms generally regulate pH precise- 

 ly, because a high or low pH can disrupt enzymatic 

 reactions, ionic/osmoregulatory control, and cell 

 membrane stability (Prosser 1973). 



Jonas et al. (1962) found a close link between blood 

 pH and mortality in trout. Death resulted when 

 blood pH was lowered with either dilute lactic acid 

 or hydrochloric acid from a normal mean pH of 7.3 

 to 6.8-6.9, a decrease of 0.4-0.5 units. Fatalities did 

 not result when injection of the same quantity of 

 either acid did not lower blood pH into this 6.8-6.9 

 range. This indicates that acidosis was the cause of 

 death rather than the acids themselves. Spiny lob- 

 sters exposed for 2 h experienced a similar 0.5 unit 

 drop in pH (7.91-7.40). Lobsters evidently have a 

 higher tolerance for acidosis than do trout, since a 

 2-h exposure was not immediately lethal. However, 

 a pH change this large must be considered a large 

 physiological perturbation. Acidosis may also com- 

 pound oxygen extraction problems, since hemocy- 

 anin oxygen affinity decreases as pH falls. Alter- 

 natively, because lactate increases hemocyanin 

 oxygen affinity (Truchot 1980; Mangum 1983), these 

 effects may offset each other. 



Crustaceans do not have efficient systems for 

 metabolizing lactate, so its removal from hemo- 

 lymph is relatively protracted (Ellington 1983). 

 Bridges and Brand (1980) subjected six species of 

 crustaceans to 5-8 h of hypoxia and observed that 

 intertidal and burrowing species returned to near 

 normal hemolymph lactate levels much faster (4-6 

 h) than subtidal, nonburrowing species (20-24 h). 

 They suggested that species more likely to en- 

 counter hypoxia in their natural environments are 

 better adapted for removing accumulated lactate 

 when aerobic conditions return. The spiny lobster, 

 as a subtidal, nonburrowing species, probably 

 removes lactate slowly even though normal concen- 

 trations were restored within 24 h. 



Spiny lobsters are ammonotelic and eliminate am- 

 monia by diffusion from the gills into the respiratory 

 stream and out into the water. Removing spiny 



49 



