Talk about a real estate bubble: A new report from the United Nations Environment Program estimates that a square kilometer of mangrove or coral reef can be worth over $1 million per square kilometer per year for the economies of tropical nations.

More precisely, that's the average value of the ecosystem services coral reefs and mangroves provide -- from nurturing fisheries to protecting coastlines from the erosive forces of wind and waves.

The report is full of amazing numbers -- too many to recount here entertainingly, so check out the report itself (PDF file). Here are just a few high points from UNEP's gloss on the findings:

• The economic value of coral reefs ranges from $100,000 to $600,000 per square kilometer per year overall -- while it costs only about $775/sq km/yr to protect them.
• Reefs are worth over $1 million per square kilometer per year in parts of Southeast Asia, where reef-based fisheries generate about $4.46 million in income annually. In the Caribbean, they generate about $310 million a year.
• Mangroves are worth about $900,000/sq km/yr on average. That ranges from about $100,00/sq km/yr in American Samoa (adding up to about $50 million annually), to a whopping $3.5 million/sq km/yr in Thailand.

What do these numbers mean in terms of daily life? Well, reef fish alone may account for a full quarter of the global fish catch, feeding one billion people. Mangroves are also vital fish habitat -- one managed mangrove in Malaysia supports a fishery worth about $100 million a year in income.

Spending that $800-odd dollars/sq km/yr to preserve a square kilometer of mangrove or reef can add up to a lot of erosion mitigation. According to UNEP, an Indonesian hotel has spent about $125,000 a year over seven years restoring its 250 metre-long beach, which eroded after losing its reef protection to offshore coral mining.

And then there's the global aquaria trade. Reefs supply a large proportion of the fish and other marine critters that eventually end up in the tanks of an estimated 1.5 to 2 million people in Europe or North America -- and if managed carefully, this trade has the potential to provide livelihoods for many, says UNEP. In 2002, a kilo of fish destined for home aquaria was worth nearly $500, compared to about $6 for fish destined for pan and plate.

And finally, there are the as-yet-undiscovered benefits that the biodiversity sheltered in coral reefs and mangroves may hold for us, like new pharmaceuticals

The 2004 Indian Ocean tsunami affirmed -- in a terrible way -- the value of mangroves and coral reefs to save human lives. But our history shows over and over that some influential forces in the world hold life relatively cheap. UNEP's new report does the math: balancing the wealth mangroves and coral reefs generate against the income and resources lost when they're destroyed proves that saving them makes overwhelming economic sense.