It seems as if algae is having a profound effect on the coral reefs. Apparently, chemicals produced by certain species inhibit larval coral from settling on the hard substrates they need. Those that do settle seem stressed by the algal chemicals. This was found in at least two different species.

One species, however,  seems to send out chemicals the attracts the algae. Clearly the interdependence of the animals is important to understand and hopefully more research will be done.