How does Mangrove forests prevent Red Tide?

Answer 1

Red tides are caused by toxic dinoflagellates. These are microscopic red organisms that can have massive population booms under the correct conditions (warm water, lots of nutrients) called blooms. The water appears to turn red because of the massive number of these organisms.

I don't know how exactly mangrove forests minimize red tide blooms. It may be due to the mangrove trees removing the nutrients from the water as previously suggested. Another possibility is that the dinoflagellates are marine organisms (they live in salt water as opposed to fresh water) and mangrove trees grow in estuaries. The dinoflagellates may not be able to survive in the lower salinity of the estuary.

Answer 2

The cause of red tides is not entirely known, so it's not certain that mangrove forests prevent red tides. It is widely believed that red tides are caused by a combination of water temperature, nutrients, and sometimes lack of wind. So given these factors, its likely that mangrove forests could have a big effect on red tides by filtering nutrients out of the water. The shade provided by the mangroves might also help reduce temperature, but probably not by much. On the other hand, mangroves also reduce the wind, and dead mangrove leaves accumulate, so these factors might offset some some of the benefits.

Overall, the removal of nutrients is probably the biggest effect.