use Gimp qw(:auto);
use Gimp::Fu;

# ... 

my @species = qw( mussels squid octocerata );  # Our species of interest.

# Create a layer for each species (labelled for that species) and add it to
# the image.

foreach my $specie ( @species ) {
    my $layer = gimp_layer_new( $img, $w, $h, RGB, $specie, 50, NORMAL_MODE);
    gimp_image_add_layer($layer, -1);
}

# ...