Answer:  Exponential function
Step-by-step explanation:
A linear function is the form , where m is the constant rate of change of y with respect to x and c is the y-intercept.
 , where m is the constant rate of change of y with respect to x and c is the y-intercept.
An exponential growth function is in the form  , where r is the rate of growth (generally in percent) and A is initial value.
, where r is the rate of growth (generally in percent) and A is initial value.
If the population of a certain type of seahorse grew by 13% from year to year, then the rate of growth is 13% .
Hence it is an exponential equation.