Obviously, were a tsunami and earthquake to destroy Libreveille the human and financial cost to Gabon would be immense. Even worse, Libreville is a hub for Gabon's railroads and roads, and it is unlikely either the airport or the seaport would be able to be used for relief and rebuilding. Gabon profits from exports of gold, uranium, oil and niobium, all of which need functioning seaports. Lack of exports from Gabon for months would not be felt - except by Gabonese. Given the prevalence of malaria, AIDS and other diseases, coupled with the scarcity of doctors, one hardly need be GM Ehsan Ghaem Maghami to foresee that Gabon's position after a tsunami would be a lost endgame.
Normally, a country can survive losing a city comparable to Maputo. Mozambique does produce about one-sixth of the world's tantalum, which is used in automobiles, computers and cell phones. Unfortunately, there's more than enough supply to allow Mozambique to go offline for years. In many tsunami scenarios South Africa, Madagascar and Tanzania would be coping with their own losses, so it is unclear how much help Mozambique could get. The real problem is Mozambique is already critically short of doctors, and has a population weakened by AIDS and malaria.
Losing Maputo would be lethal.
Bandar-Abbas has an importance to Iran far out of proportion to its population. Any sort of hemorrhagic pandemic would definitely devastate Iran, even though Iran does not have quite the acute medical infrastructure shortcomings of Gabon and Mozambique. The vulnerability is trade. Certainly if the Straits of Hormuz were made impassible by sunken ships there would be serious damage to economies world-wide. Even if the Straits could be used at close to current capacity Bandar-Abbas handles the bulk of Iran's container and non-petroleum bulk shipping. Like doctors, container ports do not grow on trees, and avoiding a financial crash, given the precarious state of Iran's economy, would be nearly impossible.