how do I fill up my non-filling stacked area graph?

Question

I am trying to create a stacked area graph. I'm completely new at R so simple functions like these are still a bit hard... I used the following code:

# stacked area chart
ggplot(specimens_all_together, aes(x=`samplesite`, y =`value`, fill=`variable`)) + 
  geom_area(mapping = NULL,
            data = specimens_all_together,
            stat = "identity",
            position = "stack",
            na.rm = FALSE,
            orientation = NA,
            show.legend = NA,
            inherit.aes = TRUE,
            outline.type = "upper")

The table I am referring to (specimens_all_together_) has been loaded in from excell and kinda looks like (i simplified the names a bit):

sample site  | variable | value  
I            | worm     | 5 
I            | bird     | 6
I            |fish      | 3
II           | worm     | 0
II           | bird     | 0
III          | fish     | 1
IV           | worm     | 5
IV           | bird     | 3
IV           | fish     | 0
....         | ...      |...

but when i do all this, i get a graph with on the Y-axis indeed the values, a really nice legend with all worm, bird and fish types, on the x-axis I also see the sample site values, but the stacked graph, aka the 'fill' is missing. So its just an empty graph. What am I doing wrong???

PS: when i use the geom_bar(position='stack', stat='identity'), i do get a stacked bar plot so I am a bit confused.