this is an excerpt from an article by the WWF. admittedly, it is a few years old, but that should not affect the validity of the info. i am not invloving my opinion here, just reporting facts:
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Deforestation threatens the cradle of reef diversity

Mangroves play a crucial part in coastal tropical biodiversity. First and foremost, they act as a nursery for many species that live in and around coral reefs. The inter-weaving underwater roots in a mangrove forest create a multitude of niches where great numbers of fish, crustaceans, and turtles find shelter and breed out of reach of voracious predators found out on the reef.

A study on the Mesoamerican reef has revealed that there are as many as 25 times more fish of some species on reefs close to mangrove areas than in areas where mangroves have been cut down. This has an important effect for both the marine world and the people who rely on its resources.

"Mangroves play a vital role in coastal fisheries," says Dr Ghislaine Llewellyn, co-author of the study published in the February issue of Nature magazine. "They are incredibly important for maintaining fish diversity and abundance in the tropics."

Acting as a buffer zone between land and sea, mangroves also help create the right conditions for coral reef growth by filtering sediments and pollutants that would otherwise choke or poison the coral. Were it not for mangroves, coral reefs would be even more 'stressed' than they already are from the variety of others pressures surrounding them. Mangroves perform a similar protective function for the coastline, saving millions of dollars each year in coastal erosion damage.

Despite these multiple values, mangroves are disappearing at an alarming rate. Once abundant along tropical tidal coasts and estuaries worldwide, many mangrove forests have disappeared or are degraded today.

"The current rate of mangrove deforestation has implications not only for coral reefs and mangrove forests, but also for biodiversity, fisheries, and livelihoods in the entire region," says Dr Melanie McField, WWF's coral reef scientist on the Mesoamerican reef.