Not sure about 4 but one of the biggest causes around here is Drag net fishing. Cheers!
go do your own homework
Ocean acidity rising due to more carbon in atmosphere
Fishing with large nets-"bottom trawling" is what I think it's called...
Pollution in oceans
...I think there's others...
...Yanno, I have a feeling the OP needs to take better notes in class.
Silting from runoff.
Cyanobacteria / fungi.
Humans, humans, humans, and humans oh did I forget to say HUMANS !!
temp, toxins, humans, salinity ?.. shooting from the hip here :)
Some fishermen use Dynamite to fish, but then there is a type of sea snail that does terrible damage to coral reefs.
Are your contributors helping you write a paper for an ecology class? Lol.