regions: Marine Ecoregions of the World Data
In jebyrnes/meowR: Marine Ecoregions of the World in R

Data from http://www.marineregions.org/downloads.php. All datasets provides either as SpatialPolygonsDataFrame objects or, with .df, as data.frame objects

data(regions)
data(provinces)
data(realms)

data(regions.df)
data(provinces.df)
data(realms.df)

Spalding, M.D., Fox, H.E., Allen, G.R., Davidson, N., Ferdaña, Z.A., Finlayson, M., Halpern, B.S., Jorge, M.A., Lombana, A.L., Lourie, S.A., 2007. Marine ecoregions of the world: a bioregionalization of coastal and shelf areas. Bioscience 57, 573–583.

data(regions)
data(provinces)
data(realms)

par(mfrow=c(2,2), mar=c(0,1,2,0))
plot(regions, main="Ecoregion")
plot(provinces, lwd=2, border="red", main="Province")
plot(realms, lwd=2, border="blue", main="Realm")
par(mfrow=c(1,1), mar=c(5, 4, 4, 2) + 0.1)

#or with ggplot2
base_province_ggplot <- ggplot(provinces.df) + theme_bw() +
aes(long,lat,group=group) + 
  geom_polygon(fill=NA) +
  geom_path(color="black") +
  coord_equal() 
  
  base_province_ggplot