Mitochondria are membrane-bound cell organelles (mitochondrion, singular) that generate most of the chemical energy needed to power the cell's biochemical reactions. Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate (ATP).
        
             
        
        
        
There are several ways;
The Skeletal system protects for example the heart and several aspects of large vasculature. The skeleton also has the means to produce blood cells in the marrow of some of the bones. 
        
             
        
        
        
Assuming a 10% trophic efficiency, the herbivore (primary consumer) will get 10% of the producer energy. Then, the second consumer that eat the herbivore will get 10% of the primary consumer energy, so it is 10%*10%= 1% of the primary producers. 
Then, the t<span>ertiary consumer should get 0.1% of the primary producers' energy.</span>
        
                    
             
        
        
        
I would guess that the answer would be :'<span>These organisms dig more shallow burrows than they used to.</span>' If the crabs actively dig burrows, as many crab species do, and a layer of oil has persisted in the lower soil strata, it makes sense that the crabs would be reducing the depths of their burrows to avoid contact with the oil. The other possibility is that the crabs might might migrate to deeper waters, but this is less likely because the crabs would be evolved to utilise the intertidal zone.