Why is the Crimean peninsula so important for Russian trade?

Question

One of the major reasons why Russia is stated to be so much in the need of controlling the Crimean peninsula, is that their economy is restricted due to having too few options for sea trade, having very limited access to the sea. The north is frozen for a big part of the year, and Vladivostok is too remote, therefore they need another sea trading option.

However, even if Crimea stayed in Ukrainian hands and they blockaded the Kerch Strait and cut off Mariupol and Rostov, Russia still has over 400 km of coastline on the NE part of the Black Sea. Is that coastline so unsuited for building a sea port (or expanding existing ones, like Sochi)? Why is control over Sevastopol (in terms of sea trade) so important for the Russians, so they risk a potentially very costly war over it?

Answer 1

Military importance
There are several reasons of the importance of Crimea to Russia, the primary of which is the Sevastopol naval base, which is the largest Russian naval base on the Black sea:

• It is a comfortable harbor with extensive military and naval infrustructure, built over decades (or even centuries). It is simply difficult to replace at a reasonable cost and in a short amount of time.
• It allows Russia to control the black sea coast of its immediate neighbors, notably Ukraine and Georgia, but also other countries, and potentially teh Balkans. (See below for the map).
• The Black sea provides the shortest and the surest access to the Mediterranean sea, and by extension to the Indian Ocean and Southern Atlantic (what in US parlance is called projecting military power to the Mediterranean).

Economical importance
The OP suggest that Sevastopol is not indispensable for trade - this is correct, given that Russia still has a rather long Black sea coast line. Also, traditionally the trade in the Black sea was passing not through Sevastopol, but through Odessa (a Russian equivalent of Marseille), which is not in Crimea and still under Ukrainian control. However, any trade is largely dependent on presence of a military force, guaranteeing its protection, although this is arguably not the principal mission of the Russian Black Sea fleet.

Historical and cultural significance
Crimea was conquered by Russia from the Ottoman empire by Prince Potemkin (during the reign of Catherine II), in realizing the Peter I vision of Russian access to the warm Black sea.

Crimean war Several wars were fought in Crimea against Turkey and its allies, most notably the Crimean war, in which Britain and France militarily supported Turkey. This war is sometimes cited as the first mediatized war, as the war correspondents were present in place, and the photos were published in newspapers, and people were shocked by the explicit brutality of the war. Sevastopol is still a name of many landmarks, e.g., in France, in the memory of this war. Sevastopol sketches is a famous series of stories by Leo Tolstoy (the author of the War and Peace) about the war.

In less formal culture Sevastopol is well-known as a hot sea resort during the Soviet period (a kind of Russian Côte d'Azur), as well as for the wine making tradition - see Crimean wines.

Some additional reading
Crimea's strategic value to Russia
What is Russia doing in the Black sea?
What makes the Black sea so strategically important?

Answer 2

It's not really as important as Russian propaganda would portray. When Ukraine was in control of the peninsula it allowed Russian control of Sevastopol naval base with no problems. Also Russia has other major ports on Black Sea, including another major naval base.

It's not Crimea that's important, and not for Russians. It's gaining Crimea important, and not for Russia, but for Putin. Putin is a dictator who has everything one can imagine and a lot one cannot imagine. In all that opulence and power he wants to make the next step in what he considers his personal greatness: to go into history books as the conquerer, the "gatherer of lands". The current war in Ukraine, as well as his previous excursions into Crimea, Georgia, Moldova - all of that was his personal ego.

Apart from ego, winning small wars and gaining lands is known to be a handy tool for retaining power. Many tried before Putin, and he has done that multiple times now: enhancing his own image via nationalism and wars of conquest.

EDIT. Based on some comments I'd like to point out that Crimea isn't authentically Russian.

In fact, Crimea had very little Russian population until 1853 Crimean War and didn't have Russian majority until Stalin's ethnic cleansing of Tatars in 1944. After the genocide against the Crimean Tatars perpetrated by Russians Soviets - well, yes, after that Russians became the majority. Please take a look at how the ethnic make up of Crimea change over the years in the Ethnicities and languages table in this wikipedia article.

Therefore the pro-Putin's nationalistic meme "Крымнаш", meaning "Crimea is ours", is historically false.