For what resource might sessile animals compete?

Sessile animals compete for food, shelter (accommodation) and energy resources.

Explanation:

Sessile animals are stagnant animals (unable to loco mote) that fix to a place, object or other living species and take their nourishment form the surrounding or from the base to which they are attached.  

Competition arises when resources are limited. In such scenarios, a sessile animal compete for space, food, energy resources such as light etc. In case of sessile animals living in water, the major competition is for space and food only.  

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

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