Science Homework Help!?

I HATE SCIENCE! help is needed!
[this is a crossword]
* a community that has reached a stable stage of ecological succession [15 letters starts with p]
*Climax communities dominated by grasses [10 letters]
* water ecosystem formed from the calcium carbonate shells secreted by a particular animal [9 letters]
* the portion of the shoreline that is covered with water at high tide and exposed to the air during low tide [14 letters starts with i]
* forests dominated by trees with needle like leaves [13 letters]
* a cold forest region dominated by cone-bearing evergreen trees [5 letters]
* the area where a river meets an ocean and contains a mixture of freshwater and saltwater [7 letters]
thank you to anyone who can help