The white gooey-looking mass covering this mussel is called "didemnum", an invasive species of sea squirt that's taking over the sea bottom in various locations off the east coast.
Although it looks like mucus, this animal is fairly firm, almost leathery. It's actually a large group of sea squirts -- cloned from a single individual -- tightly packed together.
We will be running some survey missions between mid-July and mid-August to learn more about where this species lives and how it is spreading.