Do they retract their (arms) and get hard when disturbed? If they do they are almost certanly as mentioned by AdeptMrSniffles Toadstool Leather corals. But, they are usually pretty harty and not so often in groups. So, the possibility of them being Xenia, as yote said is just as valid. Xenia much more often branch out to form new colonies and can be a bit touchy. The macro setting on a camers does wonders for shots of this nature. That is a great suggestion AdeptMrSniffles. Here are a couple of pics to help you out. Xenia is on the left Toadstool is on the right. Don't place much value in color it varies greatly.
Ryan