Looking on the internet deeply has found these results:

on the sea coast is the most popular phrase on the web.

at the seaside 12,570,000 results on the web	on the sea coast 13,430,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	However, the IMP covers many EU sectoral policies with a bearing on the seas and coasts. Tomorrow I pose for fashion photos on the sea coast. The unemployment rate where I live on the North Sea coast is 11 % and rising. On the Japan Sea coast all visible to the Pacific Ocean. Made from grapes grown on the Black Sea coast. western Bulgaria, near the Romanian border. According to EurActiv.com, Turkey is planning to build a nuclear power station at ??neada, a small town close to the Bulgarian border on the Black Sea coast. Durankulak Lake is a natural firth on the Black Sea coast in north

at the seaside

12,570,000 results on the web

on the sea coast

13,430,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

However, the IMP covers many EU sectoral policies with a bearing on the seas and coasts.
Tomorrow I pose for fashion photos on the sea coast.
The unemployment rate where I live on the North Sea coast is 11 % and rising.
On the Japan Sea coast all visible to the Pacific Ocean.
Made from grapes grown on the Black Sea coast.
western Bulgaria, near the Romanian border.
According to EurActiv.com, Turkey is planning to build a nuclear power station at ??neada, a small town close to the Bulgarian border on the Black Sea coast.
Durankulak Lake is a natural firth on the Black Sea coast in north