Plotting raster maps in R

I need someone with remote sensing/GIS knowledge. I'd like to plot some maps (R code already written) but need help with overlaying coastline and land mask (similar to the Python implementation in the attached screenshot) so that land features will not show. Pls do not contact me if you don't have experience with GIS and/or plotting maps in R. I can provide more details for anyone with experience and interest. Thanks.