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Oh Buoy, Look at Those Mussels! - Hakai Institute

Oh Buoy, Look at Those Mussels!

Divers had to dig through shellfish to maintain oceanography equipment.

The red box shows the clean structure on the KC Buoy before it was deployed in 2018 (left). Tens of thousands of mussels had attached to the buoy only six months after its last cleaning. Photos by Jonathan Kellogg and Derek Van Maanen

Human-made structures placed in the ocean don’t tend to stay clean for long. Blank surfaces are a beacon for seaweeds and animals like barnacles and sponges looking for a nice place to settle, which means a buoy and its underwater oceanography sensors bobbing off the Central Coast of British Columbia are prime real estate. Time to call in the underwater maintenance crew.

In the late summer and into the fall, a team of divers from the Hakai Institute and the Central Coast Indigenous Resource Alliance (CCIRA) were stationed at the Hakai Institute’s ecological observatory on Calvert Island for six weeks of rockfish surveys. When they weren’t counting fish, the team completed other important underwater tasks.

On a brisk morning in late September, the dive team headed out 11 kilometers east of the observatory to do some maintenance on the KC Buoy at the mouth of Kwakshua Channel. Although it got a tune-up this past winter, some of the sensors needed to be inspected, others replaced, and a bit of a scrub down is always appreciated. But once they dropped below the surface, the divers realized this mission might be tougher than they initially thought.

“There were so many mussels that they built a curtain spreading across one [buoy] support to the next, affixing themselves to only their neighboring mussels,” says veteran diver Derek Van Maanen. “Not one instrument or sensor was visible.”

Tens of thousands of mussels in layers up to 30 centimeters deep—roughly equivalent to four or five bricks stacked on top of each other—had attached themselves to the equipment. This is more broadly known as biofouling, where a build-up of organisms affects the structure and function of underwater equipment.

Video by Derek Van Maanen

Hakai’s dive team joined forces with the Central Coast Indigenous Resource Alliance to do some maintenance on the KC Buoy between rockfish surveys. Photo by Derek Van Maanen

While there was some concern that all of those shellfish could affect the measurements made by sensors attached to the buoy, at least preliminarily it doesn’t look like the data varies from normal patterns.

“There are many kinds of sensors that could have data influenced by mussel growth,” says Jessy Barrette, a marine instrumentation specialist with the Hakai Institute. “But fortunately none of the sensors mounted on the buoy right now should be affected.” 

He added that biofouling is a major concern in oceanography, particularly with instruments at the surface where there tends to be more biological growth. Without cleaning by divers, the mussels’ growth goes unchecked on the buoy, as their main predator—ochre sea stars—won’t be able to get to them. 

While it wasn’t remotely the dive team’s longest or most technically challenging dive over the past few weeks, it was definitely one of the most memorable. By raining down mussels from above, they made some scavengers on the seafloor 285 meters below happy, too.

“We’ve done several dives on the buoy in the past year,” says Van Maanen. “I’ve never seen mussel growth like this before.”