#1 It's a real rose not plastic. I have no idea how it got there.
The black objects that look like small rocks near the waterline are Hercules Club Mud Whelks. They are one of the most heavily armoured mollusks you will ever see. Few creatures find it worth the effort of cracking them open; probably just as well because they are intermediate hosts of intestinal worms. But they do eventually die and their shells are put to good use by more vulnerable creatures.
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#4 Who can then relax and enjoy a sunny Queensland day.