What About 

 Sublethal Effects? 



So far, we have looked at the initial 

 mortality from the spill and the recovery 

 of affected communities. Other studies 

 of specific species have demonstrated 

 significant sublethal effects f roi ,i chronic 

 exposure of animal populations to oil. 

 These effects are reflected in the 

 physical defects and abnormal behavior 

 observed in affected animals. Sublethal 

 effects are more subtle than direct mor- 

 tality and are important to consider 

 because they may occur at very low 

 concentrations of oil and can have 

 serious long term implications in the sur- 

 vival of a species in an affected area. 



A study of the Wild Harbor marsh 

 fiddler crab {Uca pugnax) demonstrated 

 the severe chronic effects of the West 

 Falmouth spill — population densities 

 were still reduced seven years after the 

 spill. The fiddler crab is important in salt 

 marsh food webs and in energy flow 

 between the marshes and open waters. 



Krebs and Burns concluded that "oil 

 spilled in certain environments may 

 have rather short-term effects on ben- 

 thic organisms, oil stranded in marsh- 

 lands contaminates the sediments and 

 becomes incorporated in the tissues of 

 marine organisms affecting the survival 

 and recovery of marine populations for 

 many years. Recovery from even this 

 small spill of fuel oil at West Falmouth 

 is still incomplete after seven years." 



These effects were detailed in the 

 study of a single marsh species. 

 Laboratory experiments and studies of 

 other spills have shown that oil pollu- 

 tion also disrupts the functions of 

 whole communities and ecosystems. 



These disruptions are less obvious 

 than mass mortality. In a finely bal- 

 anced ecosystem they are no less 

 dangerous. The West Falmouth study 

 has shown that chronic oil pollution 

 and its insidious long term effects can 

 be caused by a single, small spill. 



Sublethal Effects on 

 Fiddler Crabs 



• Caused behavioral problems such 

 as disorientation and loss of a 

 rapid escape response. 



• Triggered physical disorders such 

 as increased molting and inappro- 

 priate display of mating colors. 



• Contributed to heavy winter mor- 

 tality through abnormally shallow 

 burrows. 



• Reduced the ratio of females to 

 males. 



• Prevented normal settlement of 

 juveniles, thereby disrupting the 

 age class distribution. 



Sublethal Effects on 

 Ecosystems 



• Disruption of normal behavior — 

 feeding, breeding, locomotion 



• Interference with thermoregula- 

 tion — control of body tem- 

 perature in birds and mammals 



• Abnormal biological processes 



• Reproductive rates 



• Growth rates 



• Competitive balance 



• Predator-prey interactions 



• Population age structure 



Fiddler Crab {Uca pugnax) 



23 



