This repo finds the population within a given distance from the coast of any ocean or a particular ocean/sea. Data comes from https://sedac.ciesin.columbia.edu/data/collection/gpw-v4.

You can edit the HTML or JS to change some style, but there is not too much else to easily modify.

Read the blog post answering some population questions at https://triplelog.com/blog/what-is-the-population-of-that-region.html