There are only a few reefs off the northeast coast of brazil, even though it lies in the tropics. why might this be?

Not all reef building corals can form in the tropics especially where rivers bring in a lot of silty sediment, which is uncommon to corals.

Iwolud you, but i dont know what you are asking.

B.) nitrogen fixationnitrogen fixation is the process of nitrogen molecules seeping into the soil and inside plant roots and bacteria. it gives more "life" to plants